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avr-libc Reference Manual

1. Note Because of the Harvard architecture of the AVR devices you must manually add 0x800000 to the address you pass to the linker as the start of the section Oth erwise the linker thinks you want to put the noinit section into the text section instead of data bss and will complain Alternatively you can write your own linker script to automate this FIXME need an example or ref to dox for writing linker scripts 7 6 6 The initN Sections These sections are used to define the startup code from reset up through the start of main These all are subparts of the text section The purpose of these sections is to allow for more specific placement of code within your program Note Sometimes it is convenient to think of the initN and finiN sections as functions but in reality they are just symbolic names the tell the linker where to stick a chunk of code which is not a function Notice that the examples for asm and C can not be called as functions and should not be jumped into The initN sections are executed in order from 0 to 9 init0 Weakly bound to __init If user defines __init it will be jumped into immediately after a reset init1 Unused User definable init2 In C programs weakly bound to initialize the stack init3 Unused User definable Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 6 Memory Sections 110 init4 Copies the data section from flash to SRAM
2. The ungetc function returns the character pushed back after the conversion or EOF if the operation fails If the value of the argument c character equals EOF the operation will fail and the stream will remain unchanged 5 12 3 31 int vfprintf FILE x __stream const char x fmt va_list _ap vfprint f is the central facility of the print f family of functions It outputs values to stream under control of a format string passed in mt The actual values to print are passed as a variable argument list ap v printf returns the number of characters written to stream or EOF in case of an error Currently this will only happen if stream has not been opened with write intent The format string is composed of zero or more directives ordinary characters not which are copied unchanged to the output stream and conversion specifications each of which results in fetching zero or more subsequent arguments Each conversion Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities 38 specification is introduced by the character The arguments must properly correspond after type promotion with the conversion specifier After the the following appear in sequence e Zero or more of the following flags The value should be converted to an alternate form For c d i s and u conversions this option has no effect For o conversions the precision of the number is increased t
3. In the AVR GCC environment the vector table is predefined to point to interrupt rou tines with predetermined names By using the appropriate name your routine will be called when the corresponding interrupt occurs The device library provides a set of default interrupt routines which will get used if you don t define your own Patching into the vector table is only one part of the problem The compiler uses by convention a set of registers when it s normally executing compiler generated code It s important that these registers as well as the status register get saved and restored The extra code needed to do this is enabled by tagging the interrupt function with _ attribute__ interrupt These details seem to make interrupt routines a little messy but all these details are handled by the Interrupt API An interrupt routine is defined with one of two macros INTERRUPTO and SIGNAL These macros register and mark the routine as an in terrupt handler for the specified peripheral The following is an example definition of a handler for the ADC interrupt include lt avr signal h gt INTERRUPT SIG_ADC user code here Refer to the chapter explaining assembler programming for an explanation about inter rupt routines written solely in assembler language If an unexpected interrupt occurs interrupt is enabled and no handler is installed which usually indicates a bug then the default action is to reset the
4. TWCR _BV TWINT _BV TWEN clear interrupt to start transmission while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_MT_DATA_ACK break case TW_MT_DATA_NACK goto quit case TW_MT_ARB_LOST goto begin default goto error must send stop condition for len gt 0 len TWDR buf TWCR _BV TWINT _BV TWEN start transmission while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_MT_DATA_NACK goto error device write protected Note 14 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI 149 case TW_MT_DATA_ACK rv break default goto error quit TWCR _BV TWINT _BV TWSTO _BV TWEN send stop condition return rv error rv 1 goto quit Wrapper around ee24xx_write_page that repeats calling this function until either an error has been returned or all bytes have been written ah int ee24xx_write_bytes uint16_t eeaddr int len uint8_t buf int rv total total 0 do if DEBUG printf Calling ee24xx_write_page d Sd p eeaddr len buf endif rv ee24xx_write_page eeaddr len buf if DEBUG printf gt Sd n rv endif if rv 1 return 1 eeaddr rv len rv buf rv total rv while len
5. must send stop condition TWDR eeaddr low 8 bits of addr TWCR _BV TWINT _BV TWEN clear interrupt to start transmission while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_MT_DATA_ACK break case TW_MT_DATA_NACK goto quit case TW_MT_ARB_LOST goto begin default goto error must send stop condition Note 10 Next cycle s master receiver mode xf TWCR _BV TWINT _BV TWSTA _BV TWEN send rep start condition while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_START OK but should not happen case TW_REP_START Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI 146 break case TW_MT_ARB_LOST goto begin default goto error send SLA R TWDR sla TW_READ TWCR _BV TWINT _BV TWEN clear interrupt to start transmission while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_MR_SLA_ACK break case TW_MR_SLA_NACK goto quit case TW_MR_ARB_LOST goto begin default goto error for twcr _BV TWINT _BV TWEN _BV TWEA Note 11 len gt 0 len if len 1 twcr _BV TWINT _BV TWEN send NAK this time TWCR twcr clear int to start transmission whi
6. 5 16 2 6 define inb sfr SFR_BYTE sfr include lt avr io h gt Read a byte from IO register sfr 5 16 2 7 define inp sfr inb sfr Deprecated For backwards compatibility only This macro will eventually be removed Use inb in new programs 5 16 2 8 define inw sfr SFR WORD sfr include lt avr io h gt Read a 16 bit word from IO register pair sfr Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 16 Special function registers 67 5 16 2 9 define loop_until_bit_is_clear sfr bit do while bit_is_set sfr bit include lt avr io h gt Wait until bit bit in IO register s fr is clear 5 16 2 10 define loop_until_bit_is_set sfr bit do while bit_is_clear sfr bit include lt avr io h gt Wait until bit bit in IO register s fr is set 5 16 2 11 define outb sfr val SFR_BYTE sfr val include lt avr io h gt Write val to IO register sfr Note The order of the arguments was switched in older versions of avr libc versions lt 20020203 5 16 2 12 define outp val sfr outb sfr val Deprecated For backwards compatibility only This macro will eventually be removed Use outb in new programs 5 16 2 13 define outw sfr val SFR_WORD sfr val include lt avr io h gt Write the 16 bit value val to IO register pair sfr Care will be taken to write the lower register first When used to update 16 bit registers where the timing is cri
7. long random r unsigned long ctx Conversion functions for double arguments Note that these functions are not located in the default library 1ibc a but in the mathematical library 1ilbm a So when linking the application the 1m option needs to be specified define DTOSTR_ALWAYS_SIGN 0x01 define DTOSTR_PLUS_SIGN 0x02 define DTOSTR_UPPERCASE 0x04 char x dtostre double __val char x__s unsigned char __prec unsigned char _ flags char x dtostrf double __val char __width char __prec char x__s Defines define RAND_MAX 0x7FFF Typedefs typedef int __compar_fn_t const void x const void x Functions _inline__ void abort void _ ATTR_NORETURN _ int abs int _1 _ ATTR_CONST__ long labs long _i _ATTR_CONST__ void x bsearch const void _ key const void __base size_t _nmemb size_t _ Size int __compar const void const void e div_t div int _num int _denom __asm__ __divmodhi4 _ATTR_CONST__ e Idivt Idiv long _num long _denom _asm__ __divmodsi4 _ATTR_ CONST_ void qsort void __base size_t __nmemb size_t __size __compar_fn_t __compar long strtol const char x__nptr char __endptr int __base unsigned long strtoul const char __nptr char __endptr int __base _inline__ long atol const char x_nptr _ATTR PURE__ inline__ int atoi const char _nptr _ATTR_PURE__ void exit int __status _ATTR_NORETURN_ Generated on Tue Apr 22 09 54 12 2003 for
8. mask fa 80 81 ld r24 Z Le 86 2b or r24 r22 fe 80 83 st Z r24 100 08 95 ret Notice that we are accessing the io port via the LD and ST instructions The port parameter must be volatile to avoid a compiler warning Note Because of the nature of the IN and OUT assembly instructions they can not be used inside the function when passing the port in this way Readers interested in the details should consult the Instruction Set data sheet Finally we come to the macro version of the operation In this contrived example the macro is the most efficient method with respect to both execution speed and code size set_bits_macro PORTB Oxf0 llc 88 b3 in r24 0x18 s 24 lle 80 6f ori r24 OxFO 240 120 88 bb out 0x18 r24 24 Of course in a real application you might be doing a lot more in your function which uses a passed by reference io port address and thus the use of a function over a macro could save you some code space but still at a cost of execution speed Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 84 Care should be taken when such an indirect port access is going to one of the 16 bit IO registers where the order of write access is critical like some timer registers All versions of avr gcc up to 3 3 will generate instructions that use the wrong access order in this situation since with normal memory operands where the order doesn t matter this som
9. 0x0062 r25 0x88 60 rl 0x88 0x0061 0x0062 0x01 ood 627 225 61 r24 0x0061 0x0062 OxFF 7 255 0x03 F 0x88 0x01 s 60 r24 0x0061 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 10 A simple project 135 8c 90 91 62 00 lds r25 0x0062 90 9b bd out Ox2b r25 43 223 8a bd out Ox2a r24 42 94 9f 91 pop 25 96 8f 91 pop r24 98 2f 91 pop r18 Ja Of 90 pop r0 962 Of be out 0x3f r0 63 Je Of 90 pop r0 ad 1f 90 pop rl a2 18 95 reti 000000a4 lt ioinit gt void ioinit void Note 5 tmrl is 10 bit PWM TCCRIA _BV PWM10 _BV PWM11 _BV XCOM11 a4 83 e8 Idi r24 0x83 TL a6 8f bd out Ox2f r24 AT tmrl running on full MCU clock TCCR1B _BV CS10 a8 81 e0 ldi r24 0x01 E aa 8e bd out 0x2e r24 46 set PWM value to 0 OCR 0 ac Tb be out Ox2b rl 43 ae la be out Ox2a rl 42 enable OC1 and PB2 as output DDROC _BV OC1 b0 88 e0 ldi r24 0x08 8 b2 87 bb out 0x17 r24 ge 123 extern inline void timer_enable_int unsigned char ints ifdef TIMSK outb TIMSK ints b4 80 e8 ldi r24 0x80 128 b6 89 bf out 0x39 r24 pad timer_enable_int _BV TOIE1 enable interrupts sei b8 78 94 sei ba 08 95 ret 000000bc lt main gt Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 10 A simple project int main void be
10. 18 92 72 00 word 0x0072 2 00000094 lt array gt 94 8c 00 word Ox008c 2 96 90 00 word 0x0090 27277 foo is at addr Ox008c bar is at addr 0x0090 array is at addr 0x0094 Then in main we see this strcpy_P buf array 1 copy bar into buf de 60 e9 ldi r22 0x90 144 e0 70 e0 ldi r23 0x00 0 e2 ce 01 movw r24 r28 e4 01 96 adiw r24 0x01 xd e6 Oe 94 79 00 call Oxf2 The addr of bar 0x0090 is loaded into the r23 r22 pair which is the second parameter passed to strcpy_P The r25 r24 pair is the addr of buf Back to FAQ Index Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 87 7 3 16 How to use external RAM Well there is no universal answer to this question it depends on what the external RAM is going to be used for Basically the bit SRE SRAM enable in the MCUCR register needs to be set in order to enable the external memory interface Depending on the device to be used and the application details further registers affecting the external memory operation like XMCRA and XMCRB and or further bits in MCUCR might be configured Refer to the datasheet for details If the external RAM is going to be used to store the variables from the C program i e the data and or bss segment in that memory area it is essential to set up the external memory interface early during the device initialization so the initialization of these
11. The strlen function returns the number of characters in src 5 3 3 8 int strncasecmp_P const char x s1 PGM_P s2 size_t n Compare two strings ignoring case The strncasecmp_P function is similar to strcasecmp_P except it only compares the first n characters of s1 Parameters si A pointer to a string in the devices SRAM s2 A pointer to a string in the devices Flash Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 4 Additional notes from lt avr sfr_defs h gt 12 n The maximum number of bytes to compare Returns The strcasecmp_P function returns an integer less than equal to or greater than zero if sl or the first n bytes thereof is found respectively to be less than to match or be greater than s2 5 3 3 9 int strncmp_P const char x s1 PGM P s2 size_t n The strncmp_P function is similar to stremp_P except it only compares the first at most n characters of sl and s2 Returns The strncmp_P function returns an integer less than equal to or greater than zero if sl or the first n bytes thereof is found respectively to be less than to match or be greater than s2 5 3 3 10 char x strncpy_P char x dest PGM P src size_t n The strncpy_P function is similar to strcpy_P except that not more than n bytes of src are copied Thus if there is no null byte among the first n bytes of src the result will not be null terminated In the case where the length of src is
12. elf S OBJCOPY j text j data O ihex lt S srec elf S OBJCOPY j text j data O srec lt C ole bin elf S OBJCOPY j text j data O binary lt Rules for building the eeprom rom images eeprom ehex ebin esrec Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI 140 ehex PRG _eeprom hex ebin PRG _eeprom bin esrec PRG _eeprom srec o _eeprom hex elf S OBJCOPY j eeprom change section lma eeprom 0 O ihex lt SR o _eeprom srec elf S OBJCOPY j eeprom change section Ima eeprom 0 O srec lt SQ _eeprom bin elf S OBJCOPY j eeprom change section lma eeprom 0 O binary lt Every thing below here is used by avr libc s build system and can be ignored by the casual user FIG2DEV fig2dev EXTRA_CLEAN_FILES hex bin srec dox eps png pdf eps PRG eps png PRG png pdf PRG pdf eps fig S FIG2DEV L eps lt e pdf fig S FIG2DEV L pdf lt C S png fig FIG2DEV L png lt SR 7 11 Example using the two wire interface TWI Some newer devices of the ATmega series contain builtin support for interfacing the mi crocontroller to a two wire bus called TWI This is essentially the same called 1178C by Philips but that term is avoided in Atmel s documentation due to patenting issues For the original Philips documentation
13. endif endif ifndef UBRR define UBRR UBRRL endif Note 3 TWI address for 24Cxx EEPROM 1 0 1 0 E2 El EO R W 1 0 1 0 E2 El A8 R W 1 0 1 0 E2 A9 A8 R W 1 0 1 0 A10 A9 A8 R W define TWI_SLA_24CXX provide a builtin TWI interface ATmegal28 0xa0 24C01 24C02 24C04 24C08 24C16 EZ El EO 000 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI 143 Maximal number of iterations to wait for a device to respond for a selection Should be large enough to allow for a pending write to complete but low enough to properly abort an infinite loop in case a slave is broken or not present at all With 100 kHz TWI clock transfering the start condition and SLA R W packet takes about 10 s The longest write period is supposed to not exceed 10 ms Thus normal operation should not require more than 100 iterations A A A F F to get the device to respond to a selection define MAX_ITER 200 Number of bytes that can be written in a row see comments for ee24xx_write_page below Some vendor s devices would accept 16 but 8 seems to be the lowest common denominator E A E e E Note that the page size must be a power of two this simplifies the page boundary calculations below define PAGE_SIZE 8 Saved TWI status register for error messages only We need to save it
14. is not large enough that is if the programmer was stupid lazy and failed to check the size before copying then anything might happen Overflowing fixed length strings is a favourite cracker technique 5 14 2 12 size_t strlcat char x dst const char src size_t siz Concatenate two strings Appends src to string dst of size siz unlike strncat siz is the full size of dst not space left At most siz 1 characters will be copied Always NULL terminates unless siz lt strlen dst Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 14 Strings 56 Returns The strlcat function returns strlen src MIN siz strlen initial dst If retval gt siz truncation occurred 5 14 2 13 size_t strlepy char x dst const char src size_t siz Copy a string Copy src to string dst of size siz At most siz 1 characters will be copied Always NULL terminates unless siz 0 Returns The strlcpy function returns strlen src If retval gt siz truncation occurred 5 14 2 14 size_t strlen const char x src Calculate the length of a string The strlen function calculates the length of the string src not including the terminat ing 10 character Returns The strlen function returns the number of characters in src 5 14 2 15 char x strlwr char x string Convert a string to lower case The strlwr function will convert a string to lower case Only the upper case alphabetic characters A
15. s a separate IO address space available as it is known from some high level CISC CPUs that can be addressed with specific IO instructions that are applicable to some or all of the IO address space in out sbi etc The entire IO address space Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 16 Special function registers 64 is also made available as memory mapped IO i e it can be accessed using all the MCU instructions that are applicable to normal data memory The IO register space is mapped into the data memory address space with an offset of 0x20 since the bottom of this space is reserved for direct access to the MCU registers Actual SRAM is available only behind the IO register area starting at either address 0x60 or 0x100 depending on the device AVR Libc supports both these paradigms While by default the implementation uses memory mapped IO access this is hidden from the programmer So the programmer can access IO registers either with a special function like outb include lt avr io h gt outb PORTA 0x33 or they can assign a value directly to the symbolic address PORTA 0x33 The compiler s choice of which method to use when actually accessing the IO port is completely independent of the way the programmer chooses to write the code So even if the programmer uses the memory mapped paradigm and writes PORTA 0x40 the compiler can optimize this into the use of an sbi instr
16. 44 abs avr_stdlib 44 acos avr_math 23 Additional notes from lt avr sfr defs h gt 11 asin avr_math 23 atan avr_math 23 atan2 avr_math 23 atoi avr_stdlib 44 atol avr_stdlib 44 AVR device specific IO definitions 6 avr_eeprom _EEGET 5 _EEPUT 5 eeprom_is_ready 5 eeprom_rb 5 eeprom_read_block 6 eeprom_read_byte 6 eeprom_read_word 6 eeprom_rw 6 eeprom_wb 6 eeprom_write_byte 6 avr_errno EDOM 19 ERANGE 19 avr interrupts cli 61 enable_external_int 62 INTERRUPT 61 sei 61 SIGNAL 61 timer_enable_int 62 avr_inttypes intl6_t 21 int32_t 21 int64_t 21 int8_t 21 intptr_t 21 uint16_t 21 uint32_t 21 uint64_t 21 uint8_t 21 uintptr_t 21 avr_math acos 23 asin 23 atan 23 atan2 23 ceil 23 cos 23 cosh 23 exp 24 fabs 24 floor 24 fmod 24 frexp 24 inverse 24 INDEX 155 isinf 24 set_sleep_mode 14 isnan 24 sleep_mode 14 Idexp 24 SLEEP_MODE_ADC 13 log 25 SLEEP_MODE_EXT_ log 10 25 STANDBY 13 M PI 23 SLEEP MODE IDLE 13 M_SQRT2 23 SLEEP_MODE_PWR_DOWN modf 25 14 pow 25 SLEEP_MODE_PWR_SAVE 14 sin 25 SLEEP_MODE STANDBY 14 sinh 25 avr_stdio sqrt 25 clearerr 32 square 25 EOF 31 tan 26 fclose 32 tanh 26 fdevopen 32 avr _pgmspace feof 33 _elpm_inline 9 ferror 33 memcpy_P 9 fgetc 33 PGM_P 8 fgets 33 PGM_VOID_P 8 FILE 31 PRG_RDB 8 fprintf 33 PSTR 9 fprintf P 34 strcasecmp_P 9 fputc 34 strcat_P 9 fputs
17. Also sets up and zeros out the bss section In Unix like targets data is normally initialized by the OS directly from the executable file Since this is impossible in an MCU environment avr gcc instead takes care of appending the data variables after text in the flash ROM image init4 then defines the code weakly bound which takes care of copying the contents of data from the flash to SRAM init5 Unused User definable init6 Unused for C programs but used for constructors in C programs init7 Unused User definable init8 Unused User definable init9 Jumps into main 7 6 7 The finiN Sections These sections are used to define the exit code executed after return from main or a call to exit These all are subparts of the text section The finiN sections are executed in descending order from 9 to 0 finit9 Unused User definable This is effectively where _exit starts fini8 Unused User definable fini7 Unused User definable fini6 Unused for C programs but used for destructors in C programs fini5 Unused User definable fini4 Unused User definable Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 6 Memory Sections 111 fini3 Unused User definable fini2 Unused User definable finil Unused User definable fini0 Goes into an infinite loop after program termination and completion of any _exit code execut
18. Character Operations 18 int isalnum int _c _ATTR CONST__ int isalpha int __c _ATTR_CONST__ int isascii int __c _ATTR_CONST__ int isblank int __c _ATTR CONST__ int isentrl int __c _ATTR_CONST__ int isdigit int __c _ATTR CONST__ int isgraph int __c _ATTR_CONST__ int islower int __c _ATTR_CONST__ int isprint int __c _ATTR CONST__ int ispunct int __c _ATTR_CONST_ int isspace int __c _ATTR CONST__ int isupper int __c _ATTR_CONST__ int isxdigit int __c _ATTR_CONST__ Character convertion routines If c is not an unsigned char value or EOF the behaviour of these functions is undefined int toascii int __c _ATTR_CONST_ int tolower int __c _ATTR_CONST__ int toupper int __c _ATTR CONST__ 5 7 2 Function Documentation 5 7 2 1 int isalnum int __c Checks for an alphanumeric character It is equivalent to isalpha c isdigit c 5 7 2 2 int isalpha int _c Checks for an alphabetic character It is equivalent to isupper c islower c 5 7 2 3 int isascii int __c Checks whether c is a 7 bit unsigned char value that fits into the ASCII character set 5 7 2 4 int isblank int _ c Checks for a blank character that is a space or a tab Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 7 Character Operations 19 5 7 2 5 int iscntrl int _ c Checks for a control character 5 7 2 6 int isdigit int __c Checks for a digit 0 through 9 5 7 2 7
19. The log function returns the natural logarithm of argument x If the argument is less than or equal 0 a domain error will occur 5 10 3 18 double log10 double _x The log function returns the logarithm of argument x to base 10 If the argument is less than or equal 0 a domain error will occur 5 10 3 19 double modf double __value double x _iptr The modf function breaks the argument value into integral and fractional parts each of which has the same sign as the argument It stores the integral part as a double in the object pointed to by iptr The modf function returns the signed fractional part of value 5 10 3 20 double pow double __x double __y The function pow returns the value of x to the exponent y 5 10 3 21 double sin double __x The sin function returns the sine of x measured in radians 5 10 3 22 double sinh double __x The sinh function returns the hyperbolic sine of x 5 10 3 23 double sqrt double __x The sqrt function returns the non negative square root of x 5 10 3 24 double square double _x The function square returns x x Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 11 Setjmp and Longjmp 27 Note This function does not belong to the C standard definition 5 10 3 25 double tan double __x The tan function returns the tangent of x measured in radians 5 10 3 26 double tanh double __x The tanh function returns the hyp
20. While some devices maintain their interrupt enable bit inside the device s register set external and timer interrupts have system wide configuration registers Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 15 Interrupts and Signals 62 Example Enable timer 1 overflow interrupts timer_enable_int _BV TOIE1 Do some work Disable all timer interrupts timer_enable_int 0 Note Be careful when you use these functions If you already have a different interrupt enabled you could inadvertantly disable it by enabling another intterupt e void enable_external_int unsigned char ints e void timer_enable_int unsigned char ints 5 15 2 Define Documentation 5 15 2 1 define cli _asm__ __volatile__ cli include lt avr interrupt h gt Disables all interrupts by clearing the global interrupt mask This function actually compiles into a single line of assembly so there is no function call overhead 5 15 2 2 define INTERRUPT signame Value void signame void __attribute__ interrupt void signame void include lt avr signal h gt Introduces an interrupt handler function that runs with global interrupts initially en abled This allows interrupt handlers to be interrupted 5 15 2 3 define sei _asm__ __volatile__ sei include lt avr interrupt h gt Enables interrupts by clearing the global interrupt mask This function actually com
21. Z are converted Non alphabetic characters will not be changed Returns The strlwr function returns a pointer to the converted string 5 14 2 16 int strncasecmp const char x s1 const char x s2 size_t len Compare two strings ignoring case The strncasecmp function is similar to strcasecmp except it only compares the first n characters of sl Returns The strncasecmp function returns an integer less than equal to or greater than zero if sl or the first n bytes thereof is found respectively to be less than to match or be greater than s2 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 14 Strings 57 5 14 2 17 char x strncat char x dest const char x src size_t len Concatenate two strings The strncat function is similar to strcat except that only the first n characters of src are appended to dest Returns The strncat function returns a pointer to the resulting string dest 5 14 2 18 int strncmp const char sI const char s2 size_t len Compare two strings The strncmp function is similar to stremp except it only compares the first at most n characters of s1 and s2 Returns The strncmp function returns an integer less than equal to or greater than zero if sl or the first n bytes thereof is found respectively to be less than to match or be greater than s2 5 14 2 19 char x strncpy char x dest const char src size_t len Copy a string The str
22. avrl attiny 15 AVR_ATtiny15__ avrl attiny28 _AVR_ATtiny28__ avr2 at90s2313 AVR_AT9082313__ avr2 at90s2323 _AVR_AT9082323__ avr2 at90s2333 _ AVR_AT90S2333__ avr2 at90s2343 _ AVR_AT90S2343 __ avr2 attiny22 _ AVR_ATtiny22__ avr2 attiny26 _AVR_ATtiny26__ avr2 at90s4414 _ AVR_AT90S4414__ avr2 at90s4433 _ AVR_AT90S4433__ avr2 at90s4434 _AVR_AT90S4434__ avr2 at90s8515 _ AVR_AT90S85 15__ avr2 at90c 8534 _AVR_AT90C8534__ avr2 at90s8535 _ AVR_AT90S8535__ avr2 at86rf401 _ AVR_AT86RF401__ avr3 atmega 103 _ AVR AT mega103__ avr3 atmega603 _ AVR _ATmega603__ avr3 at43usb320 _AVR_AT43USB320__ avr3 at43usb355 _AVR_AT43USB355__ avr3 at76c711 AVR_AT76C711__ The table Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 9 Using the GNU tools 122 Architecture MCU name Macro avr4 atmega8 _AVR_ATmega8 __ avr4 atmega8515 _AVR_ATmega8515__ avr4 atmega8535 _AVR_ATmega8535__ avr5 atmega16 _ AVR _ATmega16__ avr5 atmega161 _AVR_ATmegal61__ avr5 atmega162 _ AVR _ATmega162__ avr5 atmega 163 _ AVR_ATmega163__ avr5 atmega 169 _ AVR _ATmega169__ avr5 atmega32 _ AVR_ATmega32__ avr5 atmega323 _AVR_ATmega323 __ avr5 atmega64 _ AVR_ATmega64__ avr5 atmega128 _ AVR _ATmega128__ avr5 at94k _AVR_AT94K__ e morderl e morder2 Change the order of register assignment The default is 124 r25 r18 r19 r20 r21 r22 r23 r30 131 r26 127 r28 r29 r17 r16
23. r15 r14 r13 r12 r11 r10 19 r8 17 r6 r5 r4 13 r2 r0 rl Order 1 uses r18 r19 r20 r21 r22 r23 r24 r25 r30 r31 r26 r27 r28 r29 r17 r16 r15 r14 r13 r12 r11 r10 19 r8 17 r6 r5 r4 13 r2 r0 rl Order 2 uses r25 r24 r23 r22 r21 r20 r19 r18 r30 r31 r26 r27 r28 r29 r17 r16 r15 r14 r13 r12 r11 r10 19 r8 17 r6 r5 r4 13 r2 r1l r0 e mint8 Assume int to be an 8 bit integer Note that this is not really supported by avr libc so it should normally not be used The default is to use 16 bit integers e mno interrupts Generates code that changes the stack pointer without disabling interrupts Nor mally the state of the status register SREG is saved in a temporary register in terrupts are disabled while changing the stack pointer and SREG is restored e mcall prologues Use subroutines for function prologue epilogue For complex functions that use many registers that needs to be saved restored on function entry exit this saves some space at the cost of a slightly increased execution time Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 9 Using the GNU tools 123 minit stack nnnn Set the initial stack pointer to nnnn By default the stack pointer is initialized to the symbol __stack which is set to RAMEND by the run time initialization code mtiny stack Change only the low 8 bits of the stack pointer mno table jum
24. 2 The clock is used in timer calculations done by the compiler for the UART baud rate and the TWI clock rate Note 3 The address assigned for the 24Cxx EEPROM consists of 1010 in the upper four bits The following three bits are normally available as slave sub addresses allow ing to operate more than one device of the same type on a single bus where the actual subaddress used for each device is configured by hardware strapping How ever since the next data packet following the device selection only allows for 8 bits that are used as an EEPROM address devices that require more than 8 address bits 24C04 and above steal subaddress bits and use them for the EEPROM cell ad dress bits 9 to 11 as required This example simply assumes all subaddress bits are O for the smaller devices so the EO El and E2 inputs of the 24Cxx must be grounded Note 4 This function is used by the standard output facilities that are utilized in this ex ample for debugging and demonstration purposes Note 5 In order to shorten the data to be sent over the TWI bus the 24Cxx EEPROMs support multiple data bytes transfered within a single request maintaining an in ternal address counter that is updated after each data byte transfered successfully When reading data one request can read the entire device memory if desired the counter would wrap around and start back from 0 when reaching the end of the device Note 6 When reading the EEPROM
25. In case a master transmitter mode transfer is going to send more than one data packet all following packets will be considered data bytes to write at the in dicated address The internal address pointer will be incremented after each write operation Note 14 24Cxx devices can become write protected by strapping their 172WC pin to logic high Leaving it unconnected is explicitly allowed and constitutes logic low level 1 e no write protection In case of a write protected device all data transfer attempts will be NACKed by the device Note that some devices might not imple ment this 7 12 Deprecated List Global eeprom_rb addr Use eeprom_read_byte in new programs Global eeprom_rw addr Use eeprom_read_word in new programs Global eeprom_wb addr val Use eeprom_write_byte in new programs Global outp val sfr For backwards compatibility only This macro will eventually be removed Global inp sfr For backwards compatibility only This macro will eventually be removed Global BV bit For backwards compatibility only This macro will eventually be removed Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen Index PATH 111 PREFIX 111 prefix 111 BV avr_sfr 64 _EEGET avr_eeprom 5 EEPUT avr_eeprom 5 _ compar_fn_t avr_stdlib 43 elpm inline avr_pgmspace 9 _ malloc_heap_end avr_stdlib 50 _ malloc_heap_start avr_stdlib 50 malloc_margin avr_stdlib 50 abort avr_stdlib
26. Note avr io h already provides a sbi macro definition which can be used in C programs Back to FAQ Index Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 80 7 3 11 Why does the PC randomly jump around when single stepping through my program in avr gdb When compiling a program with both optimization 0 and debug information g which is fortunately possible in avr gcc the code watched in the debugger is opti mized code While it is not guaranteed very often this code runs with the exact same optimizations as it would run without the g switch This can have unwanted side effects Since the compiler is free to reorder code ex ecution as long as the semantics do not change code is often rearranged in order to make it possible to use a single branch instruction for conditional operations Branch instructions can only cover a short range for the target PC 63 through 64 words from the current PC If a branch instruction cannot be used directly the compiler needs to work around it by combining a skip instruction together with a relative jump r jmp instruction which will need one additional word of ROM Another side effect of optimzation is that variable usage is restricted to the area of code where it is actually used So if a variable was placed in a register at the beginning of some function this same register can be re used later on if the compiler notices that the fi
27. as a frame pointer points to local data on stack if necessary e Fixed registers r0 r1 Never allocated by gcc for local data but often used for fixed purposes rO temporary register can be clobbered by any C code except interrupt han dlers which save it may be used to remember something for a while within one piece of assembler code rl assumed to be always zero in any C code may be used to remember some thing for a while within one piece of assembler code but must then be cleared Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 85 after use clr r1 This includes any use of the mul s u instructions which return their result in r1 r0 Interrupt handlers save and clear r1 on entry and restore rl on exit in case it was non zero e Function call conventions Arguments allocated left to right r25 to r8 All arguments are aligned to start in even numbered registers odd sized arguments including char have one free register above them This allows making better use of the movw instruction on the enhanced core If too many those that don t fit are passed on the stack Return values 8 bit in r24 not r25 16 bit in r25 r24 up to 32 bits in 122 125 up to 64 bits in r18 r25 8 bit return values are zero sign extended to 16 bits by the caller unsigned char is more efficient than signed char just clr r25 Arguments to functions with variable argumen
28. as the value e M Print a linker map to stdout e Map mapfile Print a linker map to mapfile Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 9 Using the GNU tools 127 e cref Output a cross reference table to the map file in case Map is also present or to stdout e section start sectionname org Start section sectionname at absolute address org e Tbss org e Tdata org e Ttext org Start the bss data or text section at org respectively e T scriptfile Use scriptfile as the linker script replacing the default linker script De fault linker scripts are stored in a system specific location e g under usr local avr lib ldscripts on Unix systems and consist of the AVR architecture name avr2 through avr5 with the suffix x appended They describe how the various memory sections will be linked together 7 9 3 2 Passing linker options from the C compiler By default all unknown non option arguments on the avr gcc command line 1 e all filename arguments that don t have a suffix that is handled by avr gcc are passed straight to the linker Thus all files ending in o object files and a object libraries are provided to the linker System libraries are usually not passed by their explicit filename but rather using the 1 option which uses an abbreviated form of the archive filename see above avr libe ships two system libraries 1ibc a and libm a While
29. avr libc by Doxygen 5 13 General utilities 44 void x malloc size_t __size _ATTR_MALLOC__ void free void _ ptr void x calloc size_t _nele size_t __size _ATTR_MALLOC__ double strtod const char x__nptr char __endptr int rand void void srand unsigned int __seed int rand_r unsigned long ctx Variables e size_t _malloc_margin e char x __malloc_heap start e char x _malloc_heap_end 5 13 2 Define Documentation 5 13 2 1 define DTOSTR_ALWAYS_SIGN 0x01 Bit value that can be passed in flags to dtostre 5 13 2 2 define DTOSTR_PLUS_SIGN 0x02 Bit value that can be passed in flags to dtostre 5 13 2 3 define DTOSTR_UPPERCASE 0x04 Bit value that can be passed in flags to dtostre 5 13 2 4 define RAND_MAX 0x7FFF Highest number that can be generated by rand 5 13 2 5 define RANDOM MAX 0x7FFFFFFF Highest number that can be generated by random 5 13 3 Typedef Documentation 5 13 3 1 typedef int _compar fn t const void x const void x Comparision function type for qsort just for convenience Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 13 General utilities 45 5 13 4 Function Documentation 5 13 4 1 _ inline __ void abort void The abort function causes abnormal program termination to occur In the limited AVR environment execution is effectively halted by entering an infinite loop 5 13 4 2 int abs int _1 The abs function computes the absolute
30. be explicitly called by the name avr c However there s currently no support for libstdc the standard support library needed for a complete C implementation This imposes a number of restrictions on the C programs that can be compiled Among them are e Obviously none of the C related standard functions classes and template classes are available e The operators new and delete are not implemented attempting to use them will cause the linker to complain about undefined external references This could perhaps be fixed e Some of the supplied include files are not C safe i e they need to be wrapped into extern C a This could certainly be fixed too e Exceptions are not supported Since exceptions are enabled by default in the C frontend they explicitly need to be turned off using fno exceptions in the compiler options Failing this the linker will complain about an undefined external reference to _gxx_personality_sj0 Constructors and destructors are supported though including global ones When programming C in space and runtime sensitive environments like microcon trollers extra care should be taken to avoid unwanted side effects of the C calling conventions like implied copy constructors that could be called upon function invo cation etc These things could easily add up into a considerable amount of time and program memory wasted Thus casual inspection of the generated assembler code u
31. better in my opinion than using the S with the compiler because this listing includes routines from the libraries and the vector table contents Also all the fix ups have been satisfied In other words the listing generated by this option reflects the actual code that the processor will run avr objdump h S demo elf gt demo lst Here s the output as saved in the demo 1st file demo elf file format elf32 avr Sections Idx Name Size VMA LMA File off Algn 0 text 000000ca 00000000 00000000 00000094 2 0 CONTENTS ALLOC LOAD READONLY CODE 1 data 00000000 00800060 000000ca 0000015e 2 0 CONTENTS ALLOC LOAD DATA 2 085 00000003 00800060 00800060 0000015e 2 0 ALLOC 3 noinit 00000000 00800063 00800063 0000015e 2 0 CONTENTS 4 eeprom 00000000 00810000 00810000 0000015e 2 0 CONTENTS gt Stab 0000066c 00000000 00000000 00000160 2 2 CONTENTS READONLY DEBUGGING 6 stabstr 00000618 00000000 00000000 000007cc 2 0 CONTENTS READONLY DEBUGGING Disassembly of section text 00000000 lt __vectors gt Oe Oa co rjmp 20 Ox16 2 62 c0 rjmp JELIG OxCs 4 61 co rjmp 194 Oxc8 63 60 co rjmp 192 0xc8 8 5f co rjmp 190 ORCE a Oa cO rjmp 20 0x20 as 5d co rjmp 186 Oxc8 e 5c co rjmp 184 Oxc8 0 5b co rjmp 182 Oxc8 Aa 5a c0 rjmp 180 Oxc8 4 59 c0 rjmp 178 Oxc8 00000016 lt __ctors_end gt 6 11 24 eor fi t 8 1f be out Ox3E BI 63 a cf ed ldi r28 OxDF 228
32. data start Figure 1 RAM map of a device with internal RAM Finally there s a challenge to make the memory allocator simple enough so the code size requirements will remain low yet powerful enough to avoid unnecessary memory fragmentation and to get it all done with reasonably few CPU cycles since microcon trollers aren t only often low on space but also run at much lower speeds than the typical PC these days The memory allocator implemented in avr libc tries to cope with all of these con straints and offers some tuning options that can be used if there are more resources available than in the default configuration 7 5 2 Internal vs external RAM Obviously the constraints are much harder to satisfy in the default configuration where only internal RAM is available Extreme care must be taken to avoid a stack heap collision both by making sure functions aren t nesting too deeply and don t require too much stack space for local variables as well as by being cautious with allocating too much dynamic memory If external RAM is available it is strongly recommended to move the heap into the external RAM regardless of whether or not the variables from the data and bss sections are also going to be located there The stack should always be kept in internal RAM Some devices even require this and in general internal RAM can be accessed faster since no extra wait states are required When using dynamic memory allocation and stac
33. device by jumping to the reset vector You can override this by supplying a function named __vector_ default which should be defined with either SIGNAL or INTERRUPTO as such include lt avr signal h gt SIGNAL __vector_default user code here Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 15 Interrupts and Signals 60 The interrupt is chosen by supplying one of the symbols in following table Note that every AVR device has a different interrupt vector table so some signals might not be available Check the data sheet for the device you are using FIXME Fill in the blanks Gotta read those durn data sheets Note The SIGNAL and INTERRUPT macros currently cannot spell check the argu ment passed to them Thus by misspelling one of the names below in a call to SIGNAL or INTERRUPTO a function will be created that while possibly being usable as an interrupt function is not actually wired into the interrupt vector table No warning will be given about this situation Signal Name Description SIG_2WIRE_SERIAL 2 wire serial interface aka 1178C tm SIG_ADC ADC Conversion complete SIG_COMPARATOR Analog Comparator Interrupt SIG_EEPROM_READY Eeprom ready SIG_FPGA_INTERRUPTO SIG_FPGA_INTERRUPT1 SIG_FPGA_INTERRUPT2 SIG_FPGA_INTERRUPT3 SIG
34. expected to increase code size Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 9 Using the GNU tools 124 Note that at 03 gcc attempts to inline all simple functions For the AVR target this will normally constitute a large pessimization due to the code increasement The only other optimization turned on with 03 is frename registers which could rather be enabled manually instead A simple O option is equivalent to 01 Note also that turning off all optimizations will prevent some warnings from be ing issued since the generation of those warnings depends on code analysis steps that are only performed when optimizing unreachable code unused variables See also the appropriate FAQ entry for issues regarding debugging optimized code e Wa assembler options e W1 linker options Pass the listed options to the assembler or linker respectively e g Generate debugging information that can be used by avr gdb e ffreestanding Assume a freestanding environment as per the C standard This turns off au tomatic builtin functions though they can still be reached by prepending _ builtin to the actual function name It also makes the compiler not com plain when main is declared with a void return type which makes some sense in a microcontroller environment where the application cannot meaning fully provide a return value to its environment in most cases main won t even ret
35. gt 0 return total void error void Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWD 150 printf error TWI status x n twst exit 0 void main void uintl6_t a int rv uint8_t b 16 uint8_t x ioinit fdevopen uart_putchar NULL 0 for a 0 a lt 256 printf S 04x a rv ee24xx_read_bytes a 16 b if rv lt 0 error if rv lt 16 printf warning short read d n rv a rv for x 0 x lt rv x printf 02x b x putchar n define EE_WRITE addr str ee24xx_write_bytes addr sizeof str 1 str rv EE_WRITE 55 The quick brown fox jumps over the lazy dog if ev lt 0 error printf Wrote d bytes n rv for a 0 a lt 256 printf s 04x a rv ee24xx_read_bytes a 16 b if rv lt 0 error if rv lt 16 printf warning short read d n rv a rv for x 0 x lt rv x printf 02x b x putchar An printf done In Note 1 The header file lt avr io h gt contains some macro definitions for symbolic con stants used in the TWI status register These definitions match the names used in Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI the Atmel datasheet except that all names have been prefixed with TW_ Note
36. high and low byte of a 16 bit value asm volatile mov tmp_reg__ A0 n t mov A0 BO nye mov B0 __tmp_reg__ n t r value 0 value First you will notice the usage of register _tmp_reg__ which we listed among other special registers in the Assembler Code section You can use this register without saving its contents Completely new are those letters A and B in SAO and B0 In fact they refer to two different 8 bit registers both containing a part of value Another example to swap bytes of a 32 bit value asm volatile mov __tmp_reg__ A0 n t mov A0 DO n t mov D0 __tmp_reg__ n t Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 4 Inline Asm 98 mov __tmp_reg__ BO n t mov BO C0 Anite mov C0 _ tmp_reg__ n t r value 0 value If operands do not fit into a single register the compiler will automatically assign enough registers to hold the entire operand In the assembler code you use A0 to refer to the lowest byte of the first operand A1 to the lowest byte of the second operand and so on The next byte of the first operand will be B0 the next byte SCO and so on This also implies that it is often neccessary to cast the type of an input operand to the desired size A final problem may arise while using pointer register pairs If you define an input operand e ptr and the compiler selects register Z r30 r31
37. int isgraph int _c Checks for any printable character except space 5 7 2 8 int islower int __c Checks for a lower case character 5 7 2 9 int isprint int __c Checks for any printable character including space 5 7 2 10 int ispunct int _c Checks for any printable character which is not a space or an alphanumeric character 5 7 2 11 int isspace int _c Checks for white space characters For the avr libc library these are space form feed f newline n carriage return r horizontal tab t and vertical tab Av 5 7 2 12 int isupper int __c Checks for an uppercase letter 5 7 2 13 int isxdigit int _c Checks for a hexadecimal digits i e one of 0123456789abcdefABCDEF 5 7 2 14 int toascii int __c Converts c to a 7 bit unsigned char value that fits into the ASCII character set by clearing the high order bits Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 8 System Errors errno 20 Warning Many people will be unhappy if you use this function This function will convert accented letters into random characters 5 7 2 15 int tolower int _c Converts the letter c to lower case if possible 5 7 2 16 int toupper int __c Converts the letter c to upper case if possible 5 8 System Errors errno 5 8 1 Detailed Description include lt errno h gt Some functions in the library set the global variable errno when an error o
38. into the PWM register Since we are in an interrupt routine it is safe to use a 16 bit assignment to the register Outside of an interrupt the assignment should only be performed with interrupts disabled if there s a chance that an interrupt routine could also access this register or another register that uses TEMP see the appropriate FAQ entry Note 5 This routine gets called after a reset It initializes the PWM and enables interrupts Note 6 The main loop of the program does nothing all the work is done by the interrupt Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 10 A simple project 130 routine If this was a real product we d probably put a SLEEP instruction in this loop to conserve power Note 7 Early AVR devices saturate their outputs at rather low currents when sourcing cur rent so the LED can be connected directly the resulting current through the LED will be about 15 mA For modern parts at least for the ATmega 128 however Atmel has drastically increased the IO source capability so when operating at 5 V Vcc R2 is needed Its value should be about 150 Ohms When operating the circuit at 3 V it can still be omitted though 7 10 2 The Source Code A E AR RR waa a gs SS a enh pe ee RSE Se ey oe A SSsE THE BEER WARE LICENSE Revision 42 lt joerg FreeBSD ORG gt wrote this file As long as you retain this notice you can do whatever you want w
39. iterations made until the device is declared to be not responding at all and an error is returned will be limited to MAX_ITER Note 10 This is called master receiver mode the bus master still supplies the SCL clock but the device slave drives the SDA line with the appropriate data After 8 data bits the master responds with an ACK bit SDA driven low in order to request another data transfer from the slave or it can leave the SDA line high NACK indicating to the slave that it is going to stop the transfer now Assertion of ACK is handled by setting the TWEA bit in TWCR when starting the current transfer Note 11 The control word sent out in order to initiate the transfer of the next data packet is initially set up to assert the TWEA bit During the last loop iteration TWEA is de asserted so the client will get informed that no further transfer is desired Note 12 Except in the case of lost arbitration all bus transactions must properly be termi nated by the master initiating a stop condition Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 12 Deprecated List 153 Note 13 Writing to the EEPROM device is simpler than reading since only a master trans mitter mode transfer is needed Note that the first packet after the SLA W se lection is always considered to be the EEPROM address for the next operation This packet is exactly the same as the one above sent before starting to read the device
40. less than that of n the remainder of dest will be padded with nulls Returns The strncpy_P function returns a pointer to the destination string dest 5 4 Additional notes from lt avr sfr_defs h gt The lt avr sfr_defs h gt file is included by all of the lt avr ioXXXX Hh gt files which use macros defined here to make the special function register definitions look like C variables or simple constants depending on the _SFR_ASM_COMPAT define Some examples from lt avr iom128 h gt to show how to define such macros define PORTA _SFR_108 0x1b define TCNT1 _SFR_IC16 0x2c define PORTF _SFR_MEM8 0x61 define TCNT3 _SFR_MEM16 0x88 If _SFR_ASM_COMPAT is not defined C programs can use names like PORTA directly in C expressions also on the left side of assignment operators and GCC will do the Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 4 Additional notes from lt avr sfr_defs h gt 13 right thing use short I O instructions if possible The _SFR_OFFSET definition is not used in any way in this case Define SFR_ASM_COMPAT as 1 to make these names work as simple constants ad dresses of the I O registers This is necessary when included in preprocessed assem bler S source files so it is done automatically if _ASSEMBLER__ is defined By default all addresses are defined as if they were memory addresses used in lds sts instructions To use these addresses in in out instructions yo
41. list valid parts specify the v option The e option instructs avrdude to perform a chip erase before programming this is almost always necessary before programming the flash The m flash option indicates that we want to upload data into the flash memory while i main hex specifies the name of the input file The EEPROM is uploaded in the same way the only difference is that you would use m eeprom instead of m flash To use interactive mode use the t option Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 9 Using the GNU tools 120 avrdude p 2313 t avrdude AVR device initialized and ready to accept instructions avrdude Device signature 0xle9101 avrdude gt The command displays a list of valid commands avrdude gt gt gt gt Valid commands dump dump memory dump lt memtype gt lt addr gt lt N Bytes gt read alias for dump write write memory write lt memtype gt lt addr gt lt b1 gt lt b2 gt lt bN gt erase perform a chip erase sig display device signature bytes part display the current part information send send a raw command send lt bl gt lt b2 gt lt b3 gt lt b4 gt help help 2 help quit quit Use the part command to display valid memory types for use with the dump and write commands avrdude gt 7 9 Using the GNU tools This is a short summary of the AVR specific aspects of using the GNU tools Norma
42. of the project into several compiles and one link avr gcc g Os mmcu at90s2333 c demo c The compilation will create a demo o file Next we link it into a binary called demo elf avr gcc g mmcu at90s2333 o demo elf demo o It is important to specify the MCU type when linking The compiler uses the mmcu option to choose start up files and run time libraries that get linked together If this option isn t specified the compiler defaults to the 8515 processor environment which is most certainly what you didn t want 7 10 4 Examining the Object File Now we have a binary file Can we do anything useful with it besides put it into the processor The GNU Binutils suite is made up of many useful tools for manipulating object files that get generated One tool is avr objdump which takes information from the object file and displays it in many useful ways Typing the command by itself will cause it to list out its options For instance to get a feel of the application s size the h option can be used The output of this option shows how much space is used in each of the sections the st ab and stabstr sections hold the debugging information and won t make it into the ROM file Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 10 A simple project 133 An even more useful option is S This option disassembles the binary file and inter sperses the source code in the output This method is much
43. ongoing transfer from the active master In this example upon detecting a lost arbitration condition the entire transfer is going to be restarted This will cause a new start condition to be initiated which will normally be delayed until the currently active master has released the bus Note 8 Next the device slave is going to be reselected using a so called repeated start condition which is meant to guarantee that the bus arbitration will remain at the current master using the same slave address SLA but this time with read intent R 172W bit set to 1 in order to request the device slave to start transfering data from the slave to the master in the next packet Note 9 If the EEPROM device is still busy writing one or more cells after a previous write request it will simply leave its bus interface drivers at high impedance and does not respond to a selection in any way at all The master selecting the device will see the high level at SDA after transfering the SLA R W packet as a NACK to its selection request Thus the select process is simply started over effectively causing a repeated start condition until the device will eventually respond This polling procedure is recommended in the 24Cxx datasheet in order to minimize the busy wait time when writing Note that in case a device is broken and never responds to a selection e g since it is no longer present at all this will cause an infinite loop Thus the maximal number of
44. piles into a single line of assembly so there is no function call overhead Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 16 Special function registers 63 5 15 2 4 define SIGNAL signame Value void signame void __attribute__ signal void signame void include lt avr signal h gt Introduces an interrupt handler function that runs with global interrupts initially dis abled 5 15 3 Function Documentation 5 15 3 1 void enable_external_int unsigned char ints include lt avr interrupt h gt This function gives access to the gimsk register or eimsk register if using an AVR Mega device or gicr register for others Although this function is essentially the same as using the outb function it does adapt slightly to the type of device being used 5 15 3 2 void timer_enable_int unsigned char ints include lt avr interrupt h gt This function modifies the timsk register using the outb function The value you pass via ints is device specific 5 16 Special function registers 5 16 1 Detailed Description When working with microcontrollers many of the tasks usually consist of controlling the peripherals that are connected to the device respectively programming the subsys tems that are contained in the controller which by itself communicate with the circuitry connected to the controller The AVR series of microcontrollers offers two different paradigms to perform this task There
45. reused macros arises if you are using labels In such cases you may make use of the special pattern which is replaced by a unique number on each asm statement The following code had been taken from avr include iomacros h define loop_until_bit_is_clear port bit __asm__ _ volatile__ L_ sbic 30 1 n t rjmp L_ no outputs I gintB_t porti X I uint8_t bit N When used for the first time L_ may be translated to L 1404 the next usage might create L_1405 or whatever In any case the labels became unique too 7 4 6 C Stub Functions Macro definitions will include the same assembler code whenever they are referenced This may not be acceptable for larger routines In this case you may define a C stub function containing nothing other than your assembler code void delay uint8_t ms uint16_t cnt asm volatile ip L dalis lt TARVET mov SA0 A2 Ant mov B0 B2 An L dl Ant sbiw A0 1 n t brne L_dl2 n t dec 1 n t brne L_d11 n t amp w cnt ms me r delay_count i The purpose of this function is to delay the program execution by a specified number of milliseconds using a counting loop The global 16 bit variable delay_count must contain the CPU clock frequency in Hertz divided by 4000 and must have been set before calling this routine for the first time As described in the clobber section the routine uses a l
46. s transfer The last transfer will be NACKed which the client will take as an indication to not initiate further transfers int ee24xx_read_bytes uint16_t eeaddr int len uint8_t buf EE EE E CE E EE EE AECA E EE AE OE uint8_t sla twcr n 0 int rv 0 patch high bits of EEPROM address into SLA sla TWI_SLA_24CXX eeaddr gt gt 8 amp 0x07 lt lt 1 Note 6 First cycle master transmitter mode restart if n gt MAX_ITER return 1 begin TWCR _BV TWINT _BV TWSTA _BV TWEN send start condition while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_REP_START OK but should not happen case TW_START break case TW_MT_ARB_LOST Note 7 goto begin Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI 145 default return 1 error not in start condition NB do not send stop condition Note 8 send SLA W TWDR sla TW_WRITE TWCR _BV TWINT _BV TWEN clear interrupt to start transmission while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_MT_SLA_ACK break case TW_MT_SLA_NACK nack during select device busy writing Note 9 goto restart case TW_MT_ARB_LOST re arbitrate goto begin default goto error
47. see http www semiconductors philips com buses i2c inde 7 11 1 Introduction into TWI The two wire interface consists of two signal lines named SDA serial data and SCL serial clock plus a ground line of course All devices participating in the bus are connected together using open drain driver circuitry so the wires must be terminated using appropriate pullup resistors The pullups must be small enough to recharge the line capacity in short enough time compared to the desired maximal clock fre Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI 141 quency yet large enough so all drivers will not be overloaded There are formulas in the datasheet that help selecting the pullups Devices can either act as a master to the bus i e they initiate a transfer or as a slave they only act when being called by a master The bus is multi master capable and a particular device implementation can act as either master or slave at different times Devices are addressed using a 7 bit address coordinated by Philips transfered as the first byte after the so called start condition The LSB of that byte is R 172W i e it determines whether the request to the slave is to read or write data during the next cycles There is also an option to have devices using 10 bit addresses but that is not covered by this example 7 11 2 The TWI example project The ATmega TWI hardwar
48. that has been spec ified by the mmcu compiler command line switch This is done by diverting to the appropriate file lt avr ioXXXX h gt which should never be included directly Some Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 3 Program Space String Utilities register names common to all AVR devices are defined directly within lt avr io h gt but most of the details come from the respective include file Note that this file always includes include lt avr sfr_defs h gt See Special function registers for the details Included are definitions of the IO register set and their respective bit values as specified in the Atmel documentation Note that Atmel is not very consistent in its naming conventions so even identical functions sometimes get different names on different devices Also included are the specific names useable for interrupt function definitions as docu mented here Finally the following macros are defined e RAMEND A constant describing the last on chip RAM location e XRAMEND A constant describing the last possible location in RAM This is equal to RA MEND for devices that do not allow for external RAM e E2END A constant describing the address of the last EEPROM cell FLASHEND A constant describing the last byte address in flash ROM SPM_PAGESIZE For devices with bootloader support the flash pagesize in bytes to be used for the SPM instruction 5 3 Program Space
49. the new entry with possible adjacent entries yielding a single larger entry available for further allocations That way the potential for heap fragmentation is hopefully reduced 7 6 Memory Sections Remarks Need to list all the sections which are available to the avr Weak Bindings FIXME need to discuss the weak directive The following describes the various sections available 7 6 1 The text Section The text section contains the actual machine instructions which make up your program This section is further subdivided by the initN and finiN sections dicussed below Note The avr size program part of binutils coming from a Unix background doesn t account for the data initialization space added to the text section so in order to know how much flash the final program will consume one needs to add the values for both text and data but not bss while the amount of pre allocated SRAM is the sum of data and bss Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 6 Memory Sections 108 7 6 2 The data Section This section contains static data which was defined in your code Things like the fol lowing would end up in data char err_str Your program has died a horrible death struct point pt 1 1 It is possible to tell the linker the SRAM address of the beginning of the data section This is accomplished by adding W1 Tdata addr to the avr gcc command used to the link
50. the radix as base which may be a number between 2 binary conversion and up to 36 If radix is greater than 10 the next digit after 9 will be the letter a The itoa function returns the pointer passed as s 5 13 4 13 long labs long _ i The labs function computes the absolute value of the long integer i Note The abs and labs functions are builtins of gcc 5 13 4 14 Idiv_t Idiv long __num long _denom The Idiv function computes the value num denom and returns the quotient and re mainder in a structure named 1div_t that contains two long integer members named quot and rem 5 13 4 15 charx Itoa long int _ val char x _s int _radix The function Itoa converts the long integer value from val into an ASCII represen tation that will be stored under s The caller is responsible for providing sufficient storage in s Conversion is done using the radix as base which may be a number between 2 binary conversion and up to 36 If radix is greater than 10 the next digit after 9 will be the letter a The ltoa function returns the pointer passed as s Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 13 General utilities 48 5 13 4 16 void malloc size_t _ size The malloc function allocates size bytes of memory If malloc fails a NULL pointer is returned Note that malloc does not initialize the returned memory to zero bytes See the chapter about malloc u
51. the times are approximate only and apply to a supply voltage of 5 V At lower supply voltages the times will increase For older devices the times will be as large as three times when operating at Vcc 3 V while the newer devices e g ATmegal28 ATmega8 only experience a negligible change Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 7 Character Operations 17 Possible timeout values are 15 ms 30 ms 60 ms 120 ms 250 ms 500 ms 1 s 2 s Symbolic constants are formed by the prefix WDTO_ followed by the time Example that would select a watchdog timer expiry of approximately 500 ms wdt_enable WDTO_500MS 5 6 2 6 define WDTO_IS 6 See WDTO_15MS 5 6 2 7 define WDTO_250MS 4 See WDTO_15MS 5 6 2 8 define WDTO_2S 7 See WDTO_15MS 5 6 2 9 define WDTO_30MS 1 See WDTO_15MS 5 6 2 10 define WDTO_500MS 5 See WDTO_15MS 5 6 2 11 define WDTO_60MS 2 WDTO_15MS 5 7 Character Operations 5 7 1 Detailed Description These functions perform various operations on characters include lt ctype h gt Character classification routines These functions perform character classification They return true or false status de pending whether the character passed to the function falls into the function s classifi cation i e isdigit returns true if its argument is any value 0 though 9 inclusive Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 7
52. to use an externally connected EEPROM device that is removable e g SDRAM PC memory comes with an integrated TWI EEPROM that carries the RAM configuration information 7 11 3 The Source Code A A A a is att R npr e nemore sere A et sy he et e e a a THE BEER WARE LICENSE Revision 42 lt joerg FreeBSD ORG gt wrote this file As long as you retain this notice you can do whatever you want with this stuff If we meet some day and you think this stuff is worth it you can buy me a beer in return Joerg Wunsch Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI 142 SId twitest c v 1 1 2002 12 18 22 35 38 joerg_wunsch Exp Simple demo program that talks to a 24Cxx IC EEPROM using the builtin TWI interface of an ATmega device include lt inttypes h gt include lt stdio h gt include lt stdlib h gt include lt avr io h gt include lt avr twi h gt define DEBUG 1 System clock in Hz el define SYSCLK 14745600UL i Compatibility defines Note 1 Note 2 This should work on ATmega8 ATmegal63 ATmega323 and ATmegal28 IOW on all devices that On the 128 it defaults to USART 1 ifndef UCSRB ifdef UCSRIA define UCSRA UCSRIA define UCSRB UCSRIB define UBRR UBRRIL define UDR UDRI else ATmega8 define UCSRA USR define UCSRB UCR
53. use a define d constant in an asm statement Why does the PC randomly jump around when single stepping through my pro gram in avr gdb How do I trace an assembler file in avr gdb How do I pass an IO port as a parameter to a function What registers are used by the C compiler How do I put an array of strings completely in ROM How to use external RAM Which O flag to use How do I relocate code to a fixed address My UART is generating nonsense My ATmegal28 keeps crashing Port F is completely broken Why do all my foo bar strings eat up the SRAM Why does the compiler compile an 8 bit operation that uses bitwise operators into a 16 bit operation in assembly How to detect RAM memory and variable overlap problems My program doesn t recognize a variable updated within an interrupt rou tine When using the optimizer in a loop like the following one uint8_t flag while flag 0 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 75 the compiler will typically optimize the access to flag completely away since its code path analysis shows that nothing inside the loop could change the value of flag anyway To tell the compiler that this variable could be changed outside the scope of its code path analysis e g from within an interrupt routine the variable needs to be declared like volatile uint8_t flag Back to FAQ Index 7 3 3
54. value of the integer i Note The abs and labs functions are builtins of gcc 5 13 4 3 _inline__ int atoi const char _nptr The atoi function converts the initial portion of the string pointed to by nptr to integer representation It is equivalent to int strtol nptr char NULL 10 5 13 4 4 _inline__ long atol const char __nptr The atol function converts the initial portion of the string pointed to by npt r to long integer representation It is equivalent to strtol nptr char NULL 10 5 13 4 5 void bsearch const void _ key const void _base size_t _nmemb size_t _size int x _compar const void x const void The bsearch function searches an array of nmemb objects the initial member of which is pointed to by base for a member that matches the object pointed to by key The size of each member of the array is specified by size The contents of the array should be in ascending sorted order according to the compar ison function referenced by compar The compar routine is expected to have two arguments which point to the key object and to an array member in that order and should return an integer less than equal to or greater than zero if the key object is found respectively to be less than to match or be greater than the array member Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 13 General utilities 46 The bsearch function returns a pointer
55. write intent The first stream opened with read intent is assigned to st din and the first one opened with write intent is assigned to both stdout and stderr The third parameter opts is currently unused but reserved for future extensions 5 12 3 4 int feof FILE x _ stream Test the end of file flag of st ream This flag can only be cleared by acall to clearerr Note Since there is currently no notion for end of file on a device this function will always return a false value 5 12 3 5 int ferror FILE x _stream Test the error flag of st ream This flag can only be cleared by a call to clearerr 5 12 3 6 int fgetc FILE x __sfream The function fgetc reads a character from st ream It returns the character or EOF in case end of file was encountered or an error occurred The routines feof or ferror must be used to distinguish between both situations 5 12 3 7 char fgets char x __str int __size FILE _stream Read at most size 1 bytes from stream until a newline character was encoun tered and store the characters in the buffer pointed to by str Unless an error was encountered while reading the string will then be terminated with a NUL character If an error was encountered the function returns NULL and sets the error flag of stream which can be tested using ferror Otherwise a pointer to the string will be returned Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12
56. your program Not that addr must be offset by adding 0x800000 the to real SRAM address so that the linker knows that the address is in the SRAM memory space Thus if you want the data section to start at 0x1100 pass 0x801100 at the address to the linker offset explained Note When using malloc in the application which could even happen inside library calls additional adjustments are required 7 6 3 The bss Section Uninitialized global or static variables end up in the bss section 7 6 4 The eeprom Section This is where eeprom variables are stored 7 6 5 The noinit Section This sections is a part of the bss section What makes the noinit section special is that variables which are defined as such int foo __attribute__ section noinit will not be initialized to zero during startup as would normal bss data Only uninitialized variables can be placed in the noinit section Thus the following code will cause avr gcc to issue an error int bar __attribute__ section noinit Oxaa It is possible to tell the linker explicitly where to place the noinit section by adding W1 section start noinit 0x802000 to the avr gcc command line Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 6 Memory Sections 109 at the linking stage For example suppose you wish to place the noinit section at SRAM address 0x2000 avr gcc Wl section start noinit 0x802000
57. 1 avr libc Modules Here is a list of all modules Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 3 avr libc Data Structure Index EEPROM handling AVR device specific IO definitions Program Space String Utilities Power Management and Sleep Modes Watchdog timer handling Character Operations System Errors errno Integer Types Mathematics Setjmp and Longjmp Standard IO facilities General utilities Strings Interrupts and Signals Special function registers Additional notes from lt avr sfr_defs h gt 14 15 17 20 21 23 27 29 42 51 59 63 12 3 avr libc Data Structure Index 3 1 avr libc Data Structures Here are the data structures with brief descriptions div_t Idiv_t Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 4 avr libc Page Index 4 avr libc Page Index 4 1 avr libc Related Pages Here is a list of all related documentation pages Acknowledgments avr libc and assembler programs Frequently Asked Questions Inline Asm Using malloc Memory Sections Installing the GNU Tool Chain Using the avrdude program Using the GNU tools A simple project Example using the two wire interface TWI Deprecated List 5 avr libc Module Documentation 5 1 EEPROM handling 5 1 1 Detailed Description include lt avr eeprom h gt 68 69 73 91 103 107 112 118 120 128 140 153 This header file declares the i
58. 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 73 that they must be declared global in order to be acceptable for this purpose This will only work if lt avr io h gt has been included Note that the assembler or linker have no chance to check the correct spelling of an interrupt function so it should be double checked When analyzing the resulting object file using avr objdump or avr nm a name like _vector_N should appear with N being a small integer number Note 8 As explained in the section about special function registers the actual IO port address should be obtained using the macro _SFR_IO_ADDR The AT90S1200 does not have RAM thus the memory mapped approach to access the IO registers 1s not available It would be slower than using in out instructions anyway Since the operation to reload TCCNTO is time critical it is even performed before saving SREG Obviously this requires that the instructions involved would not change any of the flag bits in SREG Note 9 Interrupt routines must not clobber the global CPU state Thus it is usually neces sary to save at least the state of the flag bits in SREG Note that this serves as an example here only since actually all the following instructions would not modify SREG either but that s not commonly the case Also it must be made sure that registers used inside the interrupt routine do not conflict with those used outside In the case of a RA
59. 19 int rand_r unsigned long ctx Variant of rand that stores the context in the user supplied variable located at ct x instead of a static library variable so the function becomes re entrant 5 13 4 20 long random void The random function computes a sequence of pseudo random integers in the range of 0 to RANDOM MAX as defined by the header file lt stdlib h gt Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 13 General utilities 49 The srandom function sets its argument seed as the seed for a new sequence of pseudo random numbers to be returned by rand These sequences are repeatable by calling srandom with the same seed value If no seed value is provided the functions are automatically seeded with a value of 1 5 13 4 21 long random r unsigned long ctx Variant of random that stores the context in the user supplied variable located at ct x instead of a static library variable so the function becomes re entrant 5 13 4 22 void srand unsigned int __seed Pseudo random number generator seeding see rand 5 13 4 23 void srandom unsigned long _ seed Pseudo random number generator seeding see random 5 13 4 24 double strtod const char x _nptr char xx __endptr The strtod function converts the initial portion of the string pointed to by nptr to double representation The expected form of the string is an optional plus or minus sign followed by a seq
60. 3 c cd bf out Ox3d r28 z Ot e de c0 rjmp 156 Oxbc 00000020 lt __vector_5 gt volatile uint16_t pwm Note 1 volatile uint8_t direction Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 10 A simple project 134 SIGNAL SIG_OVERFLOW1 Note 2 20 1f 92 push Kl 22 Of 92 push r0 24 Of b6 in ro 26 3 OF 92 push ro 28 11 24 eor El 2a 2f 93 push r18 zet 82 293 push r24 2e 9f 93 push r25 switch direction Note 3 30 80 91 60 00 lds EZA 34 99 27 eor r25 56 00 97 sbiw r24 38 al 0 breq 40 3a 01 97 sbiw r24 36 gt 29 5 brne 74 case UP if pwm 1023 direction DOWN break case DOWN if pwm 0 3e 80 91 61 00 lds r24 42 90 91 62 00 lds EZ 46 01 97 sbiw r24 48 90 93 62 00 sts 0x00 4c 80 93 61 00 sts 0x00 503 80 91 61 00 lds r24 54 90 91 62 00 lds 125 58 89 2b or r24 das bl 4 brne 44 direction UP 563 10 92 60 00 sts 0x00 60 13 co rjmp 38 62 80 91 61 00 lds r24 66 90 91 62 00 lds 125 6a 01 96 adiw r24 60 90 93 62 00 sts 0x00 103 80 93 61 00 sts 0x00 74 80 91 61 00 lds r24 78 90 91 62 00 lds 25 MES 8f 5f subi r24 Te 93 40 sbci r25 80 19 4 brne 6 82 81 e0 Ldi r24 84 80 93 60 00 sts 0x00 break OCR pwm Note 4 88 80 91 61 00 lds r24 Ox3f 63 rl 0x0060 E25 0x00 0 0x62 0x01 Fa ll 0x88 0x0061 0x0062 0x01 se 62 r25 61 r24 0x0061
61. 34 stremp_P 10 fputs_P 34 strepy_P 10 fread 34 strlen_P 10 fscanf 34 strncasecmp_P 10 fscanf_P 34 strncmp_P 11 fwrite 34 strncpy_P 11 getc 31 avr_sfr getchar 31 BV 64 gets 35 bit is_clear 64 printf 35 bit_is_set 64 printf_P 35 BV 65 pute 31 cbi 65 putchar 31 inb 65 puts 35 inp 65 puts_P 35 inw 65 scanf 35 loop_until_bit_is_clear 65 scanf_P 35 loop_until_bit_is_set 66 outb 66 outp 66 outw 66 sbi 66 avr_sleep snprintf 35 snprintf_P 35 sprintf 36 sprintf_P 36 sscanf 36 sscanf_P 36 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen INDEX 156 stderr 32 memchr 51 stdin 32 mememp 52 stdout 32 memcpy 52 ungetc 36 memmove 52 vfprintf 36 memset 53 vfscanf 39 strcasecmp 53 avr_stdlib strcat 53 compar _fn t 43 strchr 53 _malloc_heap_end 50 stremp 54 malloc_heap start 50 strcpy 54 _malloc_margin 50 stricat 54 abort 44 stricpy 55 abs 44 strlen 55 atoi 44 strlwr 55 atol 44 strncasecmp 55 bsearch 44 strncat 55 calloc 45 strncmp 56 div 45 strncpy 56 DTOSTR_ALWAYS_SIGN 43 strnlen 56 DTOSTR_PLUS_SIGN 43 strrchr 56 DTOSTR_UPPERCASE 43 strrev 57 dtostre 45 strstr 57 dtostrf 45 strupr 57 exit 45 avr_watchdog free 46 wdt_disable 15 itoa 46 wdt_enable 15 labs 46 wdt reset 15 Idiv 46 WDTO_120MS 15 ltoa 46 WDTO_15MS 15 malloc 46 WDTO_1S 16 qsort 47 WDTO_250MS 16 rand 47 WDTO_2S 16 RAND MAX 43 WDTO_30MS 16 ra
62. 4 7 4 2 Assembler Code You can use the same assembler instruction mnemonics as you d use with any other AVR assembler And you can write as many assembler statements into one code string as you like and your flash memory is able to hold Note The available assembler directives vary from one assembler to another To make it more readable you should put each statement on a seperate line asm volatile nop n t nop n t nop n t nop n t 21 The linefeed and tab characters will make the assembler listing generated by the com piler more readable It may look a bit odd for the first time but that s the way the compiler creates it s own assembler code You may also make use of some special registers Symbol Register __SREG__ Status register at address 0x3F SPL H Stack pointer high byte at address 0x3E S Stack pointer low byte at address 0x3D _tmp reg_ Register r0 used for temporary storage _ Zero_reg__ Register rl always zero Register rO may be freely used by your assembler code and need not be restored at the end of your code It s a good idea to use _tmp_reg__ and _zero_reg_ instead of ro or r1 just in case a new compiler version changes the register usage definitions 7 4 3 Input and Output Operands Each input and output operand is described by a constraint string followed by a C expression in parantheses AVR GCC 3 3 knows the following constraint characters Note The
63. 8 7 11 Example using the two wire interface TWI 140 TILI Introductioninto TWI coco e 140 TALZ The TWLexample projeti co eane a dava BAS 141 GUS TOS SOME Ode see 141 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 1 AVR Libc 7 12 Deprecated List o x 3 3 ne ee e a TO Gv o 153 1 AVR Libc The latest version of this document is always available from http savannah nongnu org projects avr libc The AVR Libc package provides a subset of the standard C library for Atmel AVR 8 bit RISC microcontrollers In addition the library provides the basic startup code needed by most applications There is a wealth of information in this document which goes beyond simply describ ing the interfaces and routines provided by the library We hope that this document provides enough information to get a new AVR developer up to speed quickly using the freely available development tools binutils gcc avr libc and many others If you find yourself stuck on a problem which this document doesn t quite address you may wish to post a message to the avr gcc mailing list Most of the developers of the AVR binutils and gcc ports in addition to the devleopers of avr libc subscribe to the list so you will usually be able to get your problem resolved You can subscribe to the list at http www avr1l org mailman listinfo avr gcc list Before posting to the list you might want to try reading the Frequently Asked
64. AM as well as a version with the suffix _P where the format string is expected to reside in the flash ROM The macro PSTR explained in Program Space String Utilities becomes very handy for declaring these format strings Note 1 It might have been possible to implement a device abstraction that is compatible with fopen but since this would have required to parse a string and to take all the information needed either out of this string or out of an additional table that would need to be provided by the application this approach was not taken Note 2 This basically follows the Unix approach if a device such as a terminal needs special handling it is in the domain of the terminal device driver to provide this functionality Thus a simple function suitable as put for fdevopen that talks to a UART interface might look like this int uart_putchar char c if c An uart_putchar r loop_until_bit_is_set UCSRA UDRE UDR c return 0 Note 3 This implementation has been chosen because the cost of maintaining an alias is considerably smaller than the cost of maintaining full copies of each stream Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities 31 Yet providing an implementation that offers the complete set of standard streams was deemed to be useful Not only that writing printf instead of fprintf mystream saves typing work but sinc
65. DE_ADC _BV SMO0O ADC Noise Reduction Mode 5 5 2 2 define SLEEP _MODE_EXT_STANDBY _BV SM0 BV SM1 gt BV SM2 Extended Standby Mode Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 6 Watchdog timer handling 15 5 5 2 3 define SLEEP MODE IDLE 0 Idle mode 5 5 2 4 define SLEEP MODE_PWR_DOWN _BV SM1 Power Down Mode 5 5 2 5 define SLEEP MODE PWR SAVE _BV SM0 BV SM1 Power Save Mode 5 5 2 6 define SLEEP_MODE_STANDBY _BV SM1 BV SM2 Standby Mode 5 5 3 Function Documentation 5 5 3 1 void set_sleep_mode uint8_t mode Set the bits in the MCUCR to select a sleep mode 5 5 3 2 void sleep_mode void Put the device in sleep mode How the device is brought out of sleep mode depends on the specific mode selected with the set_sleep_mode function See the data sheet for your device for more details 5 6 Watchdog timer handling 5 6 1 Detailed Description include lt avr wdt h gt This header file declares the interface to some inline macros handling the watchdog timer present in many AVR devices In order to prevent the watchdog timer configura tion from being accidentally altered by a crashing application a special timed sequence is required in order to change it The macros within this header file handle the required sequence automatically before changing any value Interrupts will be disabled during the manipulation Note Depending on the fuse configuration of th
66. EEPROM cells fuse bits and or lock bits if their access is supported by the Atmel serial programming protocol The main flash instruction memory of the AVR can also be programmed in interactive mode however this is not very useful because one can only turn bits off The only way to turn flash bits on is to erase the entire memory using avrdude s e option avrdude is part of the FreeBSD ports system To install it simply do the following cd usr ports devel avrdude make install Once installed avrdude can program processors using the contents of the hex file specified on the command line In this example the file main hex is burned into the flash memory avrdude p 2313 e m flash i main hex avrdude AVR device initialized and ready to accept instructions avrdude Device signature 0xle9101 avrdude erasing chip avrdude done avrdude reading input file main hex avrdude input file main hex auto detected as Intel Hex avrdude writing flash 1749 0x00 avrdude 1750 bytes of flash written avrdude verifying flash memory against main hex avrdude reading on chip flash data 1749 0x00 avrdude verifying avrdude 1750 bytes of flash verified avrdude done Thank you The p 2313 option lets avrdude know that we are operating on an AT9082313 chip This option specifies the device id and is matched up with the device of the same id in avrdude s configuration file usr local etc avrdude conf To
67. I get undefined reference to for functions like sin In order to access the mathematical functions that are declared in lt math h gt the linker needs to be told to also link the mathematical library Libm a Typically system libraries like 1ibm a are given to the final C compiler command line that performs the linking step by adding a flag 1m at the end That is the initial lib and the filename suffix from the library are written immediately after a flag So for a libfoo a library 1foo needs to be provided This will make the linker search the library in a path known to the system An alternative would be to specify the full path to the 1ibm a file at the same place on the command line i e after all the object files o However since this re quires knowledge of where the build system will exactly find those library files this is deprecated for system libraries Back to FAQ Index 7 3 4 How to permanently bind a variable to a register This can be done with register unsigned char counter asm r3 See C Names Used in Assembler Code for more details Back to FAQ Index 7 3 5 How to modify MCUCR or WDTCR early The method of early initialization MCUCR WDTCR or anything else is different and more flexible in the current version Basically write a small assembler file which looks like this begin xram S Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked
68. M less device like the AT90S1200 this can only be done by agreeing on a set of registers to be used exclusively inside the interrupt routine there would not be any other chance to save a register anywhere If the interrupt routine is to be linked together with C modules care must be taken to follow the register usage guidelines imposed by the C compiler Also any register modified inside the interrupt sevice needs to be saved usually on the stack Note 10 As explained in Interrupts and Signals a global catch all interrupt handler that gets all unassigned interrupt vectors can be installed using the name _ vector_ default This must be global and obviously should end in a ret i instruc tion By default a jump to location O would be implied instead 7 3 Frequently Asked Questions 7 3 1 FAQ Index 1 My program doesn t recognize a variable updated within an interrupt routine 2 I get undefined reference to for functions like sin 3 How to permanently bind a variable to a register Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 74 V 0 Q A a BR 11 12 13 14 15 16 17 18 19 20 21 7 3 2 How to modify MCUCR or WDTCR early What is all this _BV stuff about Can I use C on the AVR Shouldn t I initialize all my variables Why do some 16 bit timer registers sometimes get trashed How do I
69. ON s o e s e na a a kk A 4 The fu ise 1 soon RE The IN Sections lt e ra s as ee eee He eS Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen CONTENTS 76 7 The HmiN Sections ooo a iere ee 110 7 6 8 Using Sections in Assembler Code 111 269 Using Sections in Code 12 1 cee ee ee ee sats 111 7 7 Installing the GNU Tool Chain 112 Ted Requited Toole tolero a do Sa 113 rez Opiomal OO yi eceania ar a 113 7 7 3 GNU Binutils for the AVR target 114 3274 GCC forthe AVR tatget gt oc ee as 115 L 1 00 eee 116 pr gli zr rerne 116 Id AREE e E a E 117 317205 GDB forthe AVR target courses 3 A 4 117 Ti SM 3 4 ene 118 et AV o e b s eee 118 7 8 Using the avrdude program 2 2 2 u u u k k k k c 2 118 TO Using thee 12 2 2 3 uo r k tens A S r la 120 7 9 1 Options for the C compiler avr gcc 1 1 221 222 120 7 9 2 Options for the assembler avr as 125 7 9 3 Controlling the linkeravr ld 126 10 Asimple projet s vs eS eh ee ee eee b RR 6 128 PAGAL The Project 4 1 ae a ok eee eee k R 128 7 10 2 The Source Code E 130 2103 Compiling and Linking 1 2 eoc 4 sara a 132 1104 Examining the Object Pile 22 4 4 5 x vik 034 K 4444s 132 7 105 Linker Map PIES 6 ih A a a 136 7 10 6 Intel Hex Piles 1 4 oe 0 2 4 A ee ea 137 7 10 7 Make Build the Project so es sosoo s 64 MG 6 39 50 13
70. ONST__ double tan double _x _ ATTR CONST__ double floor double __x _ATTR_CONST_ double ceil double __x _ATTR_CONST__ double frexp double __value int x__exp double Idexp double __x int _exp _ATTR_CONST__ double exp double _x _ATTR CONST__ double cosh double __x _ATTR_CONST__ double sinh double __x _ATTR_CONST__ double tanh double _x _ATTR CONST__ double acos double __x _ATTR_CONST__ double asin double __x _ATTR_CONST__ double atan double _ x _ATTR CONST__ double atan2 double __y double __x _ATTR CONST__ double log double _x _ATTR_CONST_ double log10 double _x _ATTR_CONST_ double pow double __x double __y _ATTR_CONST__ int isnan double __x _ATTR_CONST_ int isinf double x _ATTR_CONST_ double square double _x _ATTR CONST__ double inverse double _ATTR_CONST_ Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 10 Mathematics 5 10 2 Define Documentation 5 10 2 1 define M_PI 3 141592653589793238462643 The constant pi 5 10 2 2 define M_SQRT 2 1 4142135623730950488016887 The square root of 2 5 10 3 Function Documentation 5 10 3 1 double acos double _x The acos function computes the principal value of the arc cosine of x The returned value is in the range 0 pi radians A domain error occurs for arguments not in the range 1 1 5 10 3 2 double asin double _x The asin function computes the principal value of the arc sine of x Th
71. Ques tions chapter of this document Note This document is a work in progress As such it may contain incor rect information If you find a mistake please send an email to the avr libc dev nongnu org describing the mistake Also send us an email if you find that a specific topic is missing from the document 1 0 1 Supported Devices The following is a list of AVR devices currently supported by the library AT90S Type Devices e at90s1200 1 at90s2313 at90s2323 at90s2333 at90s2343 at90s4414 at90s4433 at90s4434 at90s8515 at90c8534 at90s8535 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 2 avr libc Module Index ATmega Type Devices e atmega8 atmega103 atmega128 atmega 16 atmega161 atmega162 atmega 163 atmega 169 atmega32 atmega323 atmega64 untested atmega8515 untested atmega8535 untested ATtiny Type Devices attiny11 1 attiny12 1 attiny15 1 attiny22 attiny26 attiny28 1 Misc Devices e at94K 2 at76c711 3 at43usb320 at43usb355 at86rf401 Note 1 Assembly only There is no support for these devices to be programmed in C since they do not have a ram based stack Note 2 The at94K devices are a combination of FPGA and AVR microcontroller TRoth 2002 11 12 Not sure of the level of support for these More information would be welcomed Note 3 The at76c711 is a USB to fast serial interface bridge chip using an AVR core 2 avr libc Module Index 2
72. Questions include lt avr io h gt section initl1 ax progbits idi r16 _BV SRE _BV SRW out _SFR_IO_ADDR MCUCR r16 end xram S Assemble it link the resulting xram o with other files in your program and this piece of code will be inserted in initialization code which is run right after reset See the linker script for comments about the new initN sections which one to use etc The advantage of this method is that you can insert any initialization code you want just remember that this is very early startup no stack and no _zero_reg__yet and no program memory space is wasted if this feature is not used There should be no need to modify linker scripts anymore except for some very spe cial cases It is best to leave __stack at its default value end of internal SRAM faster and required on some devices like ATmegal61 because of errata and add W1 Tdata 0x801100 to start the data section above the stack For more information on using sections including how to use them from C code see Memory Sections Back to FAQ Index 7 3 6 What is all this BV stuff about When performing low level output work which is a very central point in microcon troller programming it is quite common that a particular bit needs to be set or cleared in some IO register While the device documentation provides mnemonic names for the various bits in the IO registers and the AVR device specific IO definitions reflect
73. RDMAC SIG_SPI SPI Interrupt SIG_SPM_READY Store program memory ready SIG_SUSPEND_RESUME SIG_TDMAC SIG_UARTO SIG_UARTO_DATA UART 0 Data Register Empty Interrupt SIG_UARTO_RECV UART 0 Receive Complete Interrupt SIG_UARTO_TRANS UART 0 Transmit Complete Interrupt SIG_UART1 SIG_UART1_DATA UART 1 Data Register Empty Interrupt SIG_UART1_RECV UART 1 Receive Complete Interrupt SIG_UART1_TRANS UART 1 Transmit Complete Interrupt SIG_UART_DATA UART Data Register Empty Interrupt SIG_UART_RECV UART Receive Complete Interrupt SIG_UART_TRANS UART Transmit Complete Interrupt SIG_USARTO_DATA USART 0 Data Register Empty Interrupt SIG_USARTO_RECV USART 0 Receive Complete Interrupt SIG_USARTO_TRANS USART 0 Transmit Complete Interrupt SIG_USART1_DATA USART 1 Data Register Empty Interrupt SIG_USARTI_RECV USART 1 Receive Complete Interrupt SIG_USART1_TRANS USART 1 Transmit Complete Interrupt SIG_USB_HW Global manipulation of the interrupt flag The global interrupt flag is maintained in the I bit of the status register SREG e define sei __asm__ _volatile__ sei e define cli _asm__ __volatile__ cli Macros for writing interrupt handler functions e define SIGNAL signame e define INTERRUPT signame Allowing specific system wide interrupts In addition to globally enabling interrupts each device s particular interrupt needs to be enabled separately if interrupts for this device are desired
74. RFLOWO Note 7 SIG_OVERFLOWO ldi inttmp 256 tmconst fuzz out _SFR_IO_ADDR TCNTO inttmp Note 8 in intsav _SFR_IO_ADDR SREG Note 9 sbic _SFR_IO_ADDR PORTD SQUARE rjmp TE sbi _SFR_IO_ADDR PORTD SQUARE rjmp 2f t cbi _SFR_IO_ADDR PORTD SQUARE out _SFR_IO_ADDR SREG intsav reti ioinit sbi _SFR_IO_ADDR DDRD SQUARE ldi work _BV TOIEO out _SFR_IO_ADDR TIMSK work Lai work _BV CS00 tmr0 CK 1 out _SFR_IO_ADDR TCCRO work Tar work 256 tmconst out _SFR_IO_ADDR TCNTO work sei ret global __vector_default Note 10 _ vector_default Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 2 avr libc and assembler programs reti end Note 1 As in C programs this includes the central processor specific file containing the IO port definitions for the device Note that not all include files can be included into assembler sources Note 2 Assignment of registers to symbolic names used locally Another option would be to use a C preprocessor macro instead define work 16 Note 3 Our bit number for the square wave output Note that the right hand side con sists of a CPP macro which will be substituted by its value 6 in this case before actually being passed to the assembler Note 4 The assembler uses integer operations in the host defined integer size 32 bits or longer when evaluating expressions This is in contrast to the C compiler that uses the C type int by d
75. Returns The memccpy function returns a pointer to the next character in dest after val or NULL if val was not found in the first len characters of src Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 14 Strings 53 5 14 2 2 void x memchr const void x src int val size_t len Scan memory for a character The memchr function scans the first len bytes of the memory area pointed to by src for the character val The first byte to match val interpreted as an unsigned character stops the operation Returns The memchr function returns a pointer to the matching byte or NULL if the character does not occur in the given memory area 5 14 2 3 int memcmp const void s1 const void x s2 size_t len Compare memory areas The mememp function compares the first len bytes of the memory areas sl and s2 The comparision is performed using unsigned char operations Returns The memcmp function returns an integer less than equal to or greater than zero if the first len bytes of s1 is found respectively to be less than to match or be greater than the first len bytes of s2 Note Be sure to store the result in a 16 bit variable since you may get incorrect results if you use an unsigned char or char due to truncation Warning This function is not mint8 compatible although if you only care about testing for equality this function should be safe to use 5 14 2 4 void x memcpy void dest const void x s
76. SFR_BYTE sfr amp _BV bit define sbi sfr bit SFR_ BYTE sfr _BV bit define bit_is_set sfr bit inb sfr amp _B V bit define bit_is_clear sfr bit inb sfr amp _BV bit define loop_until_bit_is_set sfr bit do while bit_is_clear sfr bit define loop_until_bit_is_clear sfr bit do while bit_is_set sfr bit e e e e e e Deprecated Macros e define outp val sfr outb sfr val e define inp sfr inb sfr e define BV bit BV bit 5 16 2 Define Documentation 5 16 2 1 define BV bit 1 lt lt bit include lt avr io h gt Converts a bit number into a byte value Note The bit shift is performed by the compiler which then inserts the result into the code Thus there is no run time overhead when using _BV 5 16 2 2 define bit_is_clear sfr bit inb sfr _BV bit include lt avr io h gt Test whether bit bit in IO register s fr is clear Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 16 Special function registers 66 5 16 2 3 define bit_is_set sfr bit inb sfr amp _BV bit include lt avr io h gt Test whether bit bit in IO register s fr is set 5 16 2 4 define BV bit BV bit Deprecated For backwards compatibility only This macro will eventually be removed Use BV in new programs 5 16 2 5 define cbi sfr bit SFR_BYTE sfr amp _BV bit include lt avr io h gt Clear bit bit in IO register sfr
77. Standard IO facilities 35 5 12 3 8 int fprintf FILE x _ stream const char x _ fmt The function fprintf performs formatted output to stream See vfprintf for details 5 12 3 9 int fprintf_P FILE x __stream const char x _ fmt Variant of fprintf that uses a fmt string that resides in program memory 5 12 3 10 int fputc int _c FILE gt _stream The function fputc sends the character c though given as type int to stream It returns the character or EOF in case an error occurred 5 12 3 11 int fputs const char x __str FILE x __stream Write the string pointed to by str to stream st ream Returns 0 on success and EOF on error 5 12 3 12 int fputs_P const char __str FILE gt _stream Variant of fputs where st r resides in program memory 5 12 3 13 size_t fread void x _ ptr size_t __size size t _nmemb FILE x __stream Read nmemb objects size bytes each from stream to the buffer pointed to by ptr Returns the number of objects successfully read i e nmemb unless an input error occured or end of file was encountered feof and ferror must be used to distinguish between these two conditions 5 12 3 14 int fscanf FILE x _ stream const char x _ fmt The function f scanf performs formatted input reading the input data from st ream See vfscanf for details 5 12 3 15 int fscanf_P FILE x _ stream const char x __fmt Variant of fscanf using a fmt string in progra
78. String Utilities 5 3 1 Detailed Description tinclude lt avr io h gt tinclude lt avr pgmspace h gt The functions in this module provide interfaces for a program to access data stored in program space flash memory of the device In order to use these functions the target device must support either the LPM or ELPM instructions Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 3 Program Space String Utilities Note These function are an attempt to provide some compatibility with header files that come with IAR C to make porting applications between different compilers eas ier This is not 100 compatibility though GCC does not have full support for multiple address spaces yet Note If you are working with strings which are completely based in ram use the stan dard string functions described in Strings Defines e define PSTR s static char __c PROGMEM s _c e define PRG_RDB addr _LPM unsigned short addr e define PGM_P const prog_char x e define PGM_VOID_P const prog_void x Functions unsigned char __elpm_inline unsigned long __addr _ATTR_CONST__ void x memcpy_P void x PGM_VOID_P size_t int strcasecmp_P const char x PGM_P __ATTR_PURE__ char strcat_P char x PGM_P int stremp_P const char x PGM_P _ATTR_PURE__ char strcpy_P char x PGM_P size_t strlen_P PGM_P _ATTR CONST__ int strncasecmp_P const char x PGM P size_t _ATTR_PURE__ int strncmp_P c
79. _FPGA_INTERRUPT4 SIG_FPGA_INTERRUPTS SIG_FPGA_INTERRUPT6 SIG_FPGA_INTERRUPT7 SIG_FPGA_INTERRUPT8 SIG_FPGA_INTERRUPT9 SIG_FPGA_INTERRUPT10 SIG_FPGA_INTERRUPT11 SIG_FPGA_INTERRUPT12 SIG_FPGA_INTERRUPT13 SIG_FPGA_INTERRUPT14 SIG_FPGA_INTERRUPT15 SIG_INPUT_CAPTURE1 Input Capture1 Interrupt SIG_INPUT_CAPTURE3 Input Capture3 Interrupt SIG_INTERRUPTO External Interrupt0 SIG_INTERRUPT1 External Interrupt1 SIG INTERRUPT2 External Interrupt2 SIG_INTERRUPT3 External Interrupt3 SIG INTERRUPT4 External Interrupt4 SIG_INTERRUPTS External Interrupt5 SIG_INTERRUPT6 External Interrupt6 SIG_INTERRUPT7 External Interrupt7 SIG_OUTPUT_COMPAREO Output Compare0 Interrupt SIG_OUTPUT_COMPAREIA Output Compare1 A Interrupt SIG_OUTPUT_COMPAREIB Output Compare1 B Interrupt SIG_OUTPUT_COMPAREIC Output Compare1 C Interrupt SIG_OUTPUT_COMPARE2 Output Compare2 Interrupt SIG_OUTPUT_COMPARE3A Output Compare3 A Interrupt SIG_OUTPUT_COMPARE3B Output Compare3 B Interrupt SIG_OUTPUT_COMPARE3C Output Compare3 C Interrupt SIG_OVERFLOWO Overflow0 Interrupt Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 15 Interrupts and Signals 61 Signal Name Description SIG_LOVERFLOW 1 Overflow 1 Interrupt SIG_OVERFLOW2 Overflow2 Interrupt SIG_OVERFLOW3 Overflow3 Interrupt SIG_PIN SIG_PIN CHANGEO SIG_PIN_CHANGE1 SIG_
80. a first device selection must be made with write in tent R 172W bit set to O indicating a write operation in order to transfer the EEPROM address to start reading from This is called master transmitter mode Each completion of a particular step in TWI communication is indicated by an asserted TWINT bit in TWCR An interrupt would be generated if allowed Af ter performing any actions that are needed for the next communication step the interrupt condition must be manually cleared by setting the TWINT bit Unlike with many other interrupt sources this would even be required when using a true interrupt routine since as soon as TWINT is re asserted the next bus transaction will start Note 7 Since the TWI bus is multi master capable there is potential for a bus contention when one master starts to access the bus Normally the TWI bus interface unit will detect this situation and will not initiate a start condition while the bus is busy Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI 152 However in case two masters were starting at exactly the same time the way bus arbitration works there is always a chance that one master could lose arbitration of the bus during any transmit operation A master that has lost arbitration is required by the protocol to immediately cease talking on the bus in particular it must not initiate a stop condition in order to not corrupt the
81. ady pre initialized at application startup Also since there is no notion of file whatsoever to avr libc there is no function fopen that could be used to associate a Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities 30 stream to some device See note 1 Instead the function fdevopen is provided to associate a stream to a device where the device needs to provide a function to send a character to receive a character or both There is no differentiation between text and binary streams inside avr libc Character n is sent literally down to the device s put function If the device requires a carriage return Vr character to be sent before the linefeed its put routine must implement this see note 2 For convenience the first call to fdevopen that opens a stream for reading will cause the resulting stream to be aliased to stdin Likewise the first call to fdevopen that opens a stream for writing will cause the resulting stream to be aliased to both stdout and stderr Thus if the open was done with both read and write intent all three standard streams will be identical Note that these aliases are indistinguishable from each other thus calling fclose on such a stream will also effectively close all of its aliases note 3 All the printf and scanf family functions come in two flavours the standard name where the format string is expected to be in SR
82. ailable address in the eeprom segment is also location 0x0 so there aren t any EEPROM variables 7 10 6 Intel Hex Files We have a binary of the application but how do we get it into the processor Most if not all programmers will not accept a GNU executable as an input file so we need to do a little more processing The next step is to extract portions of the binary and save the information into hex files The GNU utility that does this is called Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 10 A simple project 138 avr objcopy The ROM contents can be pulled from our projects binary and put into the file demo hex using the following command avr objcopy j text j data O ihex demo elf demo hex The resulting demo hex file contains 100000000AC062C061C060C05FCOOACOSDCOSCCOAL 100010005BC05AC059C011241FBECFEDCDBF4ECO2A 00020001F920F920FB60F9211242F938F939F93CD 100030008091600099270097A1F0019729F58091A0 10004000610090916200019790936200809361003B 00050008091610090916200892BB1F41092600050 000600013C08091610090916200019690936200AC 00070008093610080916100909162008F5F934056 1000800019F481E08093600080916100909162009A 00090009BBD8ABD9F918F912F910F900FBEOF90A6 000A0001F90189583E88FBD81E08EBDIBBCIABCE4 1000B00088E087BB80E889BF78940895CFEDDOEODI 0A00COOODEBFCDBFEFDFFFCF9BCF07 00000001FF The j option indicates that we want the information from the text and data segment extracted If we spec
83. am execution contin ues as if the corresponding call of setjmp had just returned the value __ret Note longjmp cannot cause 0 to be returned If longjmp is invoked with a second argument of 0 1 will be returned instead Parameters _jmpb Information saved by a previous call to setjmp ret Value to return to the caller of setjmp Returns This function never returns 5 11 2 2 int setjmp jmp_buf _jmpb Save stack context for non local goto include lt setjmp h gt Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities setjmp saves the stack context environment in __jmpb for later use by longjmp The stack context will be invalidated if the function which called setjmp returns Parameters _jmpb Variable of type jmp_buf which holds the stack information such that the environment can be restored Returns setimp returns O if returning directly and non zero when returning from longjmp using the saved context 5 12 Standard IO facilities 5 12 1 Detailed Description tinclude lt stdio h gt Warning This implementation of the standard IO facilities is new to avr libc It is not yet expected to remain stable so some aspects of the API might change in a future release This file declares the standard IO facilities that are implemented in avr libc Due to the nature of the underlying hardware only a limited subset of standard IO is im plemented There
84. aracters which is also the default value except for the c conversion that defaults to 1 The following conversion flags are supported e Matches a literal character This is not a conversion e d Matches an optionally signed decimal integer the next pointer must be a pointer to int e i Matches an optionally signed integer the next pointer must be a pointer to int The integer is read in base 16 if it begins with Ox or OX in base 8 if it begins with 0 and in base 10 otherwise Only characters that correspond to the base are used Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities 41 o Matches an octal integer the next pointer must be a pointer to unsigned int u Matches an optionally signed decimal integer the next pointer must be a pointer to unsigned int x Matches an optionally signed hexadecimal integer the next pointer must be a pointer to unsigned int f Matches an optionally signed floating point number the next pointer must be a pointer to float e g E G Equivalent to f s Matches a sequence of non white space characters the next pointer must be a pointer to char and the array must be large enough to accept all the sequence and the terminating NUL character The input string stops at white space or at the maximum field width whichever occurs first c Matches a sequence of width count characters default 1 the next pointer must be a pointer to char and
85. atic and will include the appropriate options to locate required include files in the filesystem e The invokation of the linker will be automatic and will include the appropri ate options to locate additional libraries as well as the application start up code crt XXX and linker script Note that the invokation of the C preprocessor will be automatic when the filename provided for the assembler file ends in S the capital letter s This would even apply to operating systems that use case insensitive filesystems since the actual decision is made based on the case of the filename suffix given on the command line not based on the actual filename from the file system Alternatively the language can explicitly be specified using the x assembler with cpp option 7 2 3 Example program The following annotated example features a simple 100 kHz square wave generator using an AT90S1200 clocked with a 10 7 MHz crystal Pin PD6 will be used for the square wave output include lt avr io h gt Note 1 work 16 Note 2 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 2 avr libc and assembler programs tmp EF inttmp 19 intsav 0 SQUARE PD6 Note 3 Note 4 tmconst 10700000 200000 100 kHz gt 200000 edges s fuzz 8 clocks in ISR until TCNTO is set section text global main Note 5 main reall ioinit lg rjmp ib Note 6 global SIG_OVE
86. avr libc Reference Manual 20030417cvs Generated by Doxygen 1 2 18 Tue Apr 22 09 54 05 2003 CONTENTS Contents 1 AVR Libe 2 1 0 1 Supported Devices ee ee 2 2 avr libc Module Index 3 2 1 avelibe Modules o o ks s ee ae 3 3 avr libc Data Structure Index 3 1 avr libc Data Structures h Lk k ka 8 b ee 4 4 avr libc Page Index 5 4 ayrlbe Related Pages 1 3 32 icons RR 5 5 avr libc Module Documentation 5 3L EEPROM handling gt epes Fsk Gas B K Dw 6 3 Xw 3 5 SLI Detailed Description gt e ss m v kk G ee itede 5 5 1 2 Define Documentation o Va p d kkk 6 5 1 3 Function Documentation s ce sp ban o e sk 7 5 2 AVR device specific IO definitions 7 5 3 Program Space String Utilities 2 2 2 a 8 5 3 1 Detaled Description gt lt e cs 4 6b bukka VK 8 332 Delme Documentation ss o ce val 8 Gea en k wu 9 333 Funcbron Documentati n 1 s se os k bk duk ks ks 10 5 4 Additional notes from lt avr sfrdefsh gt 12 5 5 Power Management and Sleep Modes 14 331 Detaled Description s s c s Goe a kG Oe a 3 AR 4 5 14 553 2 Delme Documentafi m 2 a o u ska au k a 14 533 Fim ton Doctmentati fi gt o soaa pioa ea 15 56 Watchdog timer bandling lt lt scoos RE CR 38 44 15 20 1 Detailed Deseripiiin lt 21 264 oros ie 4 k u 15 3 6 2 Define Documentation 2 2 1 4 1 km eac a
87. avr_string 57 strtod avr_stdlib 48 strtol avr_stdlib 48 strtoul avr_stdlib 49 strupr avr_string 57 supported devices System Errors errno 19 tan avr_math 26 tools optional 112 tools required 112 toupper ctype 19 uint16_t avr_inttypes 21 uint32_t avr_inttypes 21 uint64_t avr_inttypes 21 uint8_t avr_inttypes 21 uintptr_t avr_inttypes 21 ultoa avr_stdlib 50 ungetc avr_stdio 36 utoa avr_stdlib 50 vfprintf avr_stdio 36 vfscanf avr_stdio 39 Watchdog timer handling 14 wdt_disable avr_watchdog 15 wdt_enable avr_watchdog 15 wdt_reset avr_watchdog 15 WDTO_120MS avr watchdog 15 WDTO_15MS avr_watchdog 15 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen INDEX 162 WDTO_1S avr_watchdog 16 WDTO_250MS avr_watchdog 16 WDTO_2S avr_watchdog 16 WDTO_30MS avr_watchdog 16 WDTO_500MS avr_watchdog 16 WDTO_60MS avr_watchdog 16 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen
88. by Doxygen 7 4 Inline Asm 92 Note that this document does not cover file written completely in assembler language refer to avr libc and assembler programs for this Copyright C 2001 2002 by egnite Software GmbH Permission is granted to copy and distribute verbatim copies of this manual provided that the copyright notice and this permission notice are preserved on all copies Permis sion is granted to copy and distribute modified versions of this manual provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one This document describes version 3 3 of the compiler There may be some parts which hadn t been completely understood by the author himself and not all samples had been tested so far Because the author is German and not familiar with the English language there are definitely some typos and syntax errors in the text As a programmer the author knows that a wrong documentation sometimes might be worse than none Any way he decided to offer his little knowledge to the public in the hope to get enough response to improve this document Feel free to contact the author via e mail For the latest release check http www ethernut de Herne 17th of May 2002 Harald Kipp harald kipp egnite de Note As of 26th of July 2002 this document has been merged into the documentation for avr libc The latest version is now available at http savannah nongnu org proj
89. ccurs The file lt errno h gt provides symbolic names for various error codes Warning The errno global variable is not safe to use in a threaded or multi task system A race condition can occur if a task is interrupted between the call which sets error and when the task examines errno If another task changes errno during this time the result will be incorrect for the interrupted task Defines e define EDOM 33 e define ERANGE 34 5 8 2 Define Documentation 5 8 2 1 Hdefine EDOM 33 Domain error 5 8 2 2 define ERANGE 34 Range error Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 9 Integer Types 21 5 9 Integer Types 5 9 1 Detailed Description include lt inttypes h gt Use ulintN_t if you need exactly N bits Since these typedefs are mandated by the C99 standard they are preferred over rolling your own typedefs Note If avr gcc s mint 8 option is used no 32 bit types will be available 8 bit types e typedef signed char int8_t e typedef unsigned char uint8_t 16 bit types e typedef int intl6_t e typedef unsigned int uint16_t 32 bit types e typedef long int32_t e typedef unsigned long uint32_t 64 bit types e typedef long long int64_t e typedef unsigned long long uint64_t Pointer types These allow you to declare variables of the same size as a pointer e typedef int16_t intptr_t e typedef uint16_t uintptr_t Generated on Tue Apr 22 09 54 12 2003
90. cf ed ldi r28 OxDF x 223 be d0 e0 ldi r29 0x00 70 co de bf out Ox3e r29 62 eZ cd bf out Ox3d r28 so 61 ioinit c4 ef af rcall 34 Oxa4 loop forever the interrupts are doing the rest for Note 6 ces EE Cf rjmp 2 Oxc6 000000c8 lt __bad_interrupt gt c8 9b cf rjmp 202 0x0 7 10 5 Linker Map Files avr objdump is very useful but sometimes it s necessary to see information about the link that can only be generated by the linker A map file contains this information A map file is useful for monitoring the sizes of your code and data It also shows where modules are loaded and which modules were loaded from libraries It is yet another view of your application To get a map file I usually add Wl Map demo map to my link command Relink the application using the following command to generate demo map a portion of which is shown below avr gcc g mmcu at90s2313 Wl Map demo map o demo elf demo o Some points of interest in the demo map file are rela plt rela plt text 0x00000000 Oxca vectors vectors 0x00000000 OXIE 4 u sfa ho0bj avt ertljo tts2313 0 0x00000000 vectors 0x00000000 __vector_default 0x00000016 _ ctors_start The text segment where program instructions are stored starts at location 0x0 finr2 1 fin Fini0 0x000000ca _etext data 0x00800060 0x0 load address 0x000000ca Generated on Tue Apr 22 09 54 12 2003 for avr libc b
91. const char _ fmt Like sprintf but instead of assuming s to be of infinite size no more than n characters including the trailing NUL character will be converted to s Returns the number of characters that would have been written to s if there were enough space Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities 37 5 12 3 25 int snprintf_P char x _s size_t _n const char _ fmt Variant of snprint f that uses a fmt string that resides in program memory 5 12 3 26 int sprintf char x __s const char x __fmt Variant of printf that sends the formatted characters to string s 5 12 3 27 int sprintf P char _s const char x _fmt Variant of sprintf that uses a fmt string that resides in program memory 5 12 3 28 int sscanf const char _buf const char x _fmt The function sscanf performs formatted input reading the input data from the buffer pointed to by buf See vfscanf for details 5 12 3 29 int sscanf_P const char x _buf const char x __fmt Variant of sscanf using a fmt string in program memory 5 12 3 30 int ungetc int _c FILE x _ stream The ungetc function pushes the character c converted to an unsigned char back onto the input stream pointed to by stream The pushed back character will be returned by a subsequent read on the stream Currently only a single character can be pushed back onto the stream
92. ction instead of passing the address of PORTB e g memory mapped io addr of 0x38 io port 0x18 for the megal28 This is seen clearly when looking at the disassembly of the call set_bits_func_wrong PORTB Oxaa 10a 6a ea ldi r22 OxAA 170 106 88 b3 in r24 0x18 24 10e Oe 94 65 00 call Oxca So the function once called only sees the value of the port register and knows nothing about which port it came from At this point whatever object code is generated for Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 83 the function by the compiler is irrelevant The interested reader can examine the full disassembly to see the the function s body is completely fubar The second function shows how to pass by reference the memory mapped address of the io port to the function so that you can read and write to it in the function Here s the object code generated for the function call set_bits_func_correct amp PORTB 0x55 1124 65 e5 ldi r22 0x55 x 385 114 88 e3 1di r24 0x38 s 56 116 90 e0 ldi 25 00200 t 118 Oe 94 7c 00 call Oxf8 You can clearly see that 0x0038 is correctly passed for the address of the io port Looking at the disassembled object code for the body of the function we can see that the function is indeed performing the operation we intended void set_bits_func_correct volatile uint8_t port uint8_t mask 8 fc 01 movw r30 r24 port
93. ction ultoa converts the unsigned long integer value from val into an ASCII representation that will be stored under s The caller is responsible for providing suf ficient storage in s Conversion is done using the radix as base which may be a number between 2 binary conversion and up to 36 If radix is greater than 10 the next digit after 9 will be the letter a The ultoa function returns the pointer passed as s 5 13 4 28 char utoa unsigned int __val char x __s int __radix The function utoa converts the unsigned integer value from val into an ASCII repre sentation that will be stored under s The caller is responsible for providing sufficient storage in s Conversion is done using the radix as base which may be a number between 2 binary conversion and up to 36 If radix is greater than 10 the next digit after 9 will be the letter a The utoa function returns the pointer passed as s 5 13 5 Variable Documentation 5 13 5 1 char _malloc_heap_end malloc tunable 5 13 5 2 charx _malloc_heap_start malloc tunable 5 13 5 3 size t _malloc_margin malloc tunable 5 14 Strings 5 14 1 Detailed Description include lt string h gt Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 14 Strings 52 The string functions perform string operations on NULL terminated strings Note If the strings you are working on resident in program space flash you will nee
94. ctions like sin What is all this BVO stuff about Can I use C on the AVR 2 2 2 2 22 2 Why do some 16 bit timer registers sometimes get trashed How do I use a define d constant in an asm statement Why does the PC randomly jump around when single stepping How do I pass an IO port as a parameter to a function Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen CONTENTS iv 1314 Fado 7 3 16 13147 7 3 18 Ta 1 3 20 1 321 T My UART is generating nonsense My ATmega128 keeps How to detect RAM memory and variable overlap problems TA DIA cios red aa v sk A t 741 7 4 2 7 4 3 TAA 7 4 5 7 4 6 TAT 7 4 8 GCC apm SOLEMENE o He ee ks o odo Re Input and Output Operands 4 4 2 o kl Man a maa aan Assembler Macros lt lt od oo k RO C Stub Funchons ca es ee aoee ee Ge are BAS C Names Used in Assembler Code To Usme malloc eos a van sa Bee GE eS Tal 15 2 Tad 7 5 4 a a ee as uk ER oe Hoki we 8 43 Internal vs extemal RAM ocios dentes Tunables for malloc lt lt 24 44 s Vk d eed x vla s Implementation details 111 cs 344 s kk ba eases 16 Memory Secuons 2 lt 2 13 ciao ee 8 sk kM 76 1 12 TO 7 6 4 7 6 5 7 6 6 The IEXESECU N cose eo A sk s BE The data Section i ecce nmn s BAK pk e GA ku The bss Section saec foe ee tiea a E i eS The eeprom SOCH
95. d to use the string functions described in Program Space String Utilities Functions void x memccpy void x const void x int size_t void x memchr const void x int size_t _ATTR_PURE_ int memcmp const void const void x size_t _ATTR PURE__ void x memcpy void x const void x size_t void x memmove void x const void x size_t void memset void x int size_t int strcasecmp const char x const char x _ATTR PURE__ char x strcat char x const char x char x strchr const char x int _ATTR PURE__ int stremp const char const char x _ATTR_PURE__ char x strcpy char x const char size_t strlcat char x const char x size_t size_t strlcpy char x const char x size_t size_t strlen const char x _ATTR PURE__ char x strlwr char x int strncasecmp const char x const char x size_t _ATTR PURE__ char x strncat char x const char x size_t int strncmp const char x const char x size_t char strncpy char x const char x size_t size_t strnlen const char x size_t _ATTR PURE__ char x strrchr const char x int _ATTR_PURE_ char x strrev char x char x strstr const char x const char x __ATTR_PURE__ char x strupr char x 5 14 2 Function Documentation 5 14 2 1 void x memccpy void x dest const void src int val size_t len Copy memory area The memccpy function copies no more than len bytes from memory area src to mem ory area dest stopping when the character val is found
96. d LI adiw w I and LI andi d M asr r belr I bld LI brbc Llabel brbs Llabel bset I bst LI cbi LI cbr dI com r cp LI cpc LI cpi d M cpse rr dec r elpm tz eor rr in LI inc r ld re ldd r b ldi d M lds r label lpm t z Is r Isr r mov rr mul rr neg r or LI ori d M out Lr pop r push r rol r ror r sbc LI sbci d M sbi LI sbic LI sbiw w I sbr d M sbrc LI sbrs LI ser d st er std br sts labeLr sub LI subi d M swap r Constraint characters may be prepended by a single constraint modifier Contraints without a modifier specify read only operands Modifiers are Modifier Specifies Write only operand usually used for all output operands Read write operand not supported by inline assembler amp Register should be used for output only Output operands must be write only and the C expression result must be an lvalue which means that the operands must be valid on the left side of assignments Note that the compiler will not check if the operands are of reasonable type for the kind of operation used in the assembler instructions Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 4 Inline Asm 97 Input operands are you guessed it read only But what if you need the same operand for input and output As stated above read write operands are not supported in inline assembler code But there is another solution For input operators it is possible to use a single digit in t
97. dest and then adds a terminating 0 character The strings may not overlap and the dest string must have enough space for the result Returns The strcat function returns a pointer to the resulting string dest Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 14 Strings 55 5 14 2 9 char x strchr const char src int val Locate character in string The strchr function returns a pointer to the first occurrence of the character val in the string src Here character means byte these functions do not work with wide or multi byte characters Returns The strchr function returns a pointer to the matched character or NULL if the character is not found 5 14 2 10 int stremp const char x s1 const char s2 Compare two strings The stremp function compares the two strings sl and s2 Returns The stremp function returns an integer less than equal to or greater than zero if sl is found respectively to be less than to match or be greater than s2 5 14 2 11 char x strcpy char x dest const char src Copy a string The strcpy function copies the string pointed to by src including the terminating 0 character to the array pointed to by dest The strings may not overlap and the destination string dest must be large enough to receive the copy Returns The strcpy function returns a pointer to the destination string dest Note If the destination string of a strcpy
98. dio 32 fdevopen avr_stdio 32 feof avr_stdio 33 ferror avr_stdio 33 fgetc avr_stdio 33 fgets Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen INDEX 158 avr_stdio 33 FILE avr_stdio 31 floor avr_math 24 fmod avr_math 24 fprintf avr_stdio 33 fprintf_P avr_stdio 34 fputc avr_stdio 34 fputs avr_stdio 34 fputs_P avr_stdio 34 fread avr_stdio 34 free avr_stdlib 46 frexp avr_math 24 fscanf avr_stdio 34 fscanf_P avr_stdio 34 fwrite avr_stdio 34 General utilities 41 getc avr_stdio 31 getchar avr_stdio 31 gets avr_stdio 35 inb avr_sfr 65 inp avr_sfr 65 installation 111 installation avarice 117 installation avr libc 115 installation avrdude 116 installation avrprog 116 installation binutils 113 installation gcc 114 Installation gdb 116 installation simulavr 117 installation uisp 115 intl6_t avr_inttypes 21 int32_t avr inttypes 21 int64 t avr_inttypes 21 int8_t avr_inttypes 21 Integer Types 20 INTERRUPT avr_interrupts 61 Interrupts and Signals 58 intptr_t avr_inttypes 21 inverse avr_math 24 inw avr_sfr 65 isalnum ctype 17 isalpha ctype 17 isascii ctype 17 isblank ctype 17 iscntrl ctype 17 isdigit ctype 18 isgraph ctype 18 isinf avr_math 24 islower ctype 18 isnan avr_math 24 isprint ctype 18 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Do
99. dulator PWM to ramp an LED on and off every two seconds An AT90S2313 processor will be used as the controller The circuit for this demonstration is shown in the schematic diagram If you have a development Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 10 A simple project 129 kit you should be able to use it rather than build the circuit for this project VCC MN IC1 1d SCK PB7 1 E R RESET MISO PB6 20K a A g MOSI PB5 Ola a Her rara PB4 18pf OCI PB3 XTAL1 PB2 AIN1 PB1 vec R enn AINO PBO oa ICP PD6 T1 PD5 TO PD4 INT1 PD3 INTO PD2 TXD PD1 RXD PDO AT90S2313P LED5MM R2 D1 D See note 7 X sl GND PRPEPFE BBE RREBE Figure 4 Schematic of circuit for demo project The source code is given in demo c For the sake of this example create a file called demo c containing this source code Some of the more important parts of the code are Note 1 The PWM is being used in 10 bit mode so we need a 16 bit variable to remember the current value Note 2 SIGNAL is a macro that marks the function as an interrupt routine In this case the function will get called when the timer overflows Setting up interrupts is explained in greater detail in Interrupts and Signals Note 3 This section determines the new value of the PWM Note 4 Here s where the newly computed value is loaded
100. e FILE _ stream char x gets char __str Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities 32 size_t fread void __ptr size_t __size size_t _nmemb FILE _ stream void clearerr FILE __stream int feof FILE x__stream int ferror FILE x__stream int vfscanf FILE x __stream const char __fmt va_list __ap int fscanf FILE x__stream const char __fmt int fscanf_P FILE __stream const char x__fmt int scanf const char x__fmt int scanf_P const char x__fmt int sscanf const char x__buf const char x__fmt int sscanf_P const char __buf const char x__fmt FILE fdevopen int put char int get void int opts __attribute__ unused 5 12 2 Define Documentation 5 12 2 1 Hdefine EOF 1 EOF declares the value that is returned by various standard IO functions in case of an error Since the AVR platform currently doesn t contain an abstraction for actual files its origin as end of file is somewhat meaningless here 5 12 2 2 define FILE struct _ file FILE is the opaque structure that is passed around between the various standard IO functions 5 12 2 3 define getc __stream fgetc __stream The macro getc used to be a fast macro implementation with a functionality iden tical to fgetc For space constraints in avr libc it is just an alias for fgetc 5 12 2 4 int getchar void fgetc stdin Th
101. e avr gcc needs to resort to pass all arguments of variadic functions on the stack as opposed to pass ing them in registers for functions that take a fixed number of parameters the ability to pass one parameter less by implying st din will also save some execu tion time Defines define getchar fgetc stdin define FILE struct _file define stdin __iob 0 define stdout _iob 1 define stderr __iob 2 define EOF 1 define putc __c _ stream fpute __c __stream define putchar __c fputc __c stdout define getc __stream fgetc __stream Functions int fclose FILE x__stream int vfprintf FILE __stream const char __fmt va_list __ap int fputc int _c FILE __stream int printf const char _ fmt int printf_P const char _ fmt int sprintf char __s const char __fmt int sprintf_P char __s const char x__fmt int snprintf char __s size_t __n const char __fmt int snprintf_P char __s size_t _n const char x__fmt int fprintf FILE __stream const char x__fmt int fprintf_P FILE __stream const char __fmt int fputs const char x__str FILE __stream int fputs_P const char __str FILE __stream int puts const char __str int puts_P const char x _ str size_t fwrite const void _ ptr size_t __size size_t _nmemb FILE _ stream int fgetc FILE _ stream int ungetc int __c FILE _ stream char x fgets char __str int _ siz
102. e macro get char reads a character from stdin Return values and error handling is identical to fgetc 5 12 2 5 define putc __c _stream fputc __c _stream The macro putc used to be a fast macro implementation with a functionality iden tical to fputc For space constraints in avr libc it is just an alias for fputc Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities 5 12 2 6 define putchar _c fputc __c stdout The macro put char sends character c to stdout 5 12 2 7 define stderr __iob 2 Stream destined for error output Unless specifically assigned identical to stdout If stderr should point to another stream the result of another fdevopen must be explicitly assigned to it without closing the previous st derr since this would also close stdout 5 12 2 8 define stdin _iob 0 Stream that will be used as an input stream by the simplified functions that don t take a stream argument The first stream opened with read intent using fdevopen will be assigned to stdin 5 12 2 9 define stdout _iob 1 Stream that will be used as an output stream by the simplified functions that don t take a stream argument The first stream opened with write intent using devopen will be assigned to both stdin and stderr 5 12 3 Function Documentation 5 12 3 1 void clearerr FILE x _stream Clear the error and end of file flags of stream 5 12 3 2 i
103. e particular device further restrictions might apply in particular it might be disallowed to turn off the watchdog timer Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 6 Watchdog timer handling 16 Defines define wdt_reset asm __volatile__ wdr define wdt_enable timeout wdt_write timeout BV WDE define wdt_disable _wdt_write 0 define WDTO_15MS 0 define WDTO_30MS 1 define WDTO_60MS 2 define WDTO_120MS 3 define WDTO_250MS 4 define WDTO_500MS 5 define WDTO_IS 6 define WDTO_2S 7 5 6 2 Define Documentation 5 6 2 1 define wdt_disable _wdt_write 0 Disable the watchdog timer if possible This attempts to turn off the WD WDTCR register E bit in the 5 6 2 2 define wdt_enable timeout _wdt_write timeout BV WDE Enable the watchdog timer configuring it for expiry after t imeout whic bination of the WDPO through WDP2 to write into the WDTCR register See also the symbolic constants WDTO_15MS et al 5 6 2 3 define wdt_reset _ asm__ __volatile__ wdr Reset the watchdog timer When the watchdog timer is enabled a call to this h is a com instruction is required before the timer expires otherwise a watchdog initiated device reset will occur 5 6 2 4 define WDTO_120MS 3 See WDTO_15MS 5 6 2 5 define WDTO_15MS 0 Symbolic constants for the watchdog timeout Since the watchdog timer is based on a free running RC oscillator
104. e returned value is in the range 0 pi radians A domain error occurs for arguments not in the range 1 1 5 10 3 3 double atan double __x The atan function computes the principal value of the arc tangent of x The returned value is in the range 0 pi radians A domain error occurs for arguments not in the range 1 1 5 10 3 4 double atan2 double _ y double __x The atan2 function computes the principal value of the arc tangent of y x using the signs of both arguments to determine the quadrant of the return value The returned value is in the range pi pi radians If both x and y are zero the global variable errno is set to EDOM 5 10 3 5 double ceil double __x The ceil function returns the smallest integral value greater than or equal to x ex pressed as a floating point number 5 10 3 6 double cos double _x The cos function returns the cosine of x measured in radians Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 10 Mathematics 25 5 10 3 7 double cosh double __x The cosh function returns the hyperbolic cosine of x 5 10 3 8 double exp double _x The exp function returns the exponential value of x 5 10 3 9 double fabs double __x The fabs function computes the absolute value of a floating point number x 5 10 3 10 double floor double __x The floor function returns the largest integral value less than or equal to x expressed as a floa
105. e supports both master and slave operation This example will only demonstrate how to use an AVR microcontroller as TWI master The imple mentation is kept simple in order to concentrate on the steps that are required to talk to a TWI slave so all processing is done in polled mode waiting for the TWI interface to indicate that the next processing step is due by setting the TWINT interrupt bit If it is desired to have the entire TWI communication happen in background all this can be implemented in an interrupt controlled way where only the start condition needs to be triggered from outside the interrupt routine There is a variety of slave devices available that can be connected to a TWI bus For the purpose of this example an EEPROM device out of the industry standard 24Cxx series has been chosen where xx can be one of 01 02 04 08 or 16 which are available from various vendors The choice was almost arbitrary mainly triggered by the fact that an EEPROM device is being talked to in both directions reading and writing the slave device so the example will demonstrate the details of both Usually there is probably not much need to add more EEPROM to an ATmega system that way the smallest possible AVR device that offers hardware TWI support is the ATmega8 which comes with 512 bytes of EEPROM which is equivalent to an 24C04 device The ATmegal28 already comes with twice as much EEPROM as the 24C16 would offer One exception might be
106. ects avr libc 7 4 1 GCC asm Statement Let s start with a simple example of reading a value from port D asm in 0 1 r value I PORTD Each asm statement is devided by colons into four parts 1 The assembler instructions defined as a single string constant o in 0 1 2 A list of output operands separated by commas Our example uses just one p value 3 A comma separated list of input operands Again our example uses one operand only I PORTD Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 4 Inline Asm 93 4 Clobbered registers left empty in our example You can write assembler instructions in much the same way as you would write assem bler programs However registers and constants are used in a different way if they refer to expressions of your C program The connection between registers and C operands is specified in the second and third part of the asm instruction the list of input and output operands respectively The general form is asm code output operand list input operand list clobber list In the code section operands are referenced by a percent sign followed by a single digit 0 refers to the first 1 to the second operand and so forth From the above example 30 refers to r value and 1 refers to I PORTD This may still look a little odd now but the syntax of an operand list will be explained soon Let us first exami
107. eeprom_rb addr 5 1 2 Define Documentation 5 1 2 1 define EEGET var addr var eeprom rb addr Read a byte from EEPROM 5 1 2 2 define EEPUT addr val eeprom_wb adadr val Write a byte to EEPROM 5 1 2 3 define eeprom is ready bit_is clear EECR EEWE Returns 1 if EEPROM is ready for a new read write operation 0 if not Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 2 AVR device specific IO definitions 5 1 2 4 define eeprom_rb addr eeprom read byte uint8_t addr Deprecated Use eeprom_read_byte in new programs 5 1 2 5 define eeprom_rw addr eeprom_read_word uint16_t addr Deprecated Use eeprom_read_word in new programs 5 1 2 6 define eeprom_wb addr val eeprom_write_byte uint8_t addr uint8_t val Deprecated Use eeprom_write_byte in new programs 5 1 3 Function Documentation 5 1 3 1 void eeprom_read_block void x buf void x addr size_t n Read a block of n bytes from EEPROM address addr to buf 5 1 3 2 uint8_t eeprom_read_byte uint8_t x addr Read one byte from EEPROM address addr 5 1 3 3 uint16_t eeprom_read_word uint16_t x addr Read one 16 bit word little endian from EEPROM address addr 5 1 3 4 void eeprom_write_byte uint8_t x addr uint8_t val Write a byte val to EEPROM address addr 5 2 AVR device specific IO definitions include lt avr io h gt This header file includes the apropriate IO definitions for the device
108. efault in order to calculate constant integer expressions In order to get a 100 kHz output we need to toggle the PD6 line 200000 times per second Since we use timer 0 without any prescaling options in order to get the desired frequency and accuracy we already run into serious timing consid erations while accepting and processing the timer overflow interrupt the timer already continues to count When pre loading the TCCNTO register we therefore have to account for the number of clock cycles required for interrupt acknowledge and for the instructions to reload TCCNTO 4 clock cycles for interrupt acknowl edge 2 cycles for the jump from the interrupt vector 2 cycles for the 2 instructions that reload TCCNTO This is what the constant fuzz is for Note 5 External functions need to be declared to be global main is the application en try point that will be jumped to from the ininitalization routine in crts1200 o0 Note 6 The main loop is just a single jump back to itself Square wave generation itself is completely handled by the timer 0 overflow interrupt service A sleep instruction using idle mode could be used as well but probably would not conserve much energy anyway since the interrupt service is executed quite frequently Note 7 Interrupt functions can get the usual names that are also available to C programs The linker will then put them into the appropriate interrupt vector slots Note Generated on Tue Apr 22 09 54
109. erbolic tangent of x 5 11 Setjmp and Longjmp 5 11 1 Detailed Description While the C language has the dreaded goto statement it can only be used to jump to a label in the same local function In order to jump directly to another non local function the C library provides the setjmp and longjmp functions setjmp and longjmp are useful for dealing with errors and interrupts encountered in a low level subroutine of a program Note setimp and longjmp make programs hard to understand and maintain If possi ble an alternative should be used For a very detailed discussion of setimp longjmp see Chapter 7 of Advanced Pro gramming in the UNIX Environment by W Richard Stevens Example include lt setjmp h gt jmp_buf env int main void if setjmp env handle error main processing loop which calls foo some where Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 11 Setjmp and Longjmp 28 void foo void blah blah blah if err longjmp env 1 Functions e int setjmp jmp_buf __jmpb e void longjmp jmp_buf _jmpb int _ret _ATTR_NORETURN_ 5 11 2 Function Documentation 5 11 2 1 void longjmp mp buf _jmpb int _ ret Non local jump to a saved stack context include lt setjmp h gt longjmp restores the environment saved by the last call of setjmp with the corre sponding _jmpb argument After longjmp is completed progr
110. ere s no universal definition for better with optimization often being a speed vs code size tradeoff See the detailed discus sion for which option affects which part of the code generation A test case was run on an ATmega128 to judge the effect of compiling the library itself using different optimization levels The following table lists the results The test case consisted of around 2 KB of strings to sort Test 1 used qsort using the standard library stremp test 2 used a function that sorted the strings by their size thus had Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 88 two calls to strlen per invocation When comparing the resulting code size it should be noted that a floating point version of fvprintf was linked into the binary in order to print out the time elapsed which is entirely not affected by the different optimization levels and added about 2 5 KB to the code Optimization Size of text Time for test 1 Time for test 2 flags 03 6898 903 us 19 7 ms 02 6666 972 us 20 1 ms Os 6618 955 us 20 1 ms Os 6474 972 us 20 1 ms mcall prologues The difference between 955 us and 972 us was just a single timer tick so take this with a grain of salt So generally it seems Os mcall prologues is the most universal best opti mization level Only applications that need to get the last few percent of speed benefit
111. etimes yields shorter code Seehttp mail nongnu org archive html avr libc dev 2003 01 msg00044 html for a possible workaround avr gcc versions after 3 3 have been fixed in a way where this optimization will be disabled if the respective pointer variable is declared to be volatile so the correct behaviour for 16 bit IO ports can be forced that way Back to FAQ Index 7 3 14 What registers are used by the C compiler e Data types char is 8 bits int is 16 bits long is 32 bits long long is 64 bits float and double are 32 bits this is the only supported floating point format pointers are 16 bits function pointers are word addresses to allow addressing the whole 128K program memory space on the ATmega devices with gt 64 KB of flash ROM There is a mint8 option see Options for the C compiler avr gcc to make int 8 bits but that is not supported by avr libc and violates C standards int must be at least 16 bits It may be removed in a future release Call used registers r18 r27 r30 r31 May be allocated by gcc for local data You may use them freely in assem bler subroutines Calling C subroutines can clobber any of them the caller is responsible for saving and restoring Call saved registers r2 r17 r28 r29 May be allocated by gcc for local data Calling C subroutines leaves them un changed Assembler subroutines are responsible for saving and restoring these registers if changed r29 r28 Y pointer is used
112. f characters to be printed from a string for s conversions e An optional 1 length modifier that specifies that the argument for the d i 0 u x or X conversion isa long int rather than int e A character that specifies the type of conversion to be applied The conversion specifiers and their meanings are e diouxX The int or appropriate variant argument is converted to signed deci mal d and i unsigned octal o unsigned decimal u or unsigned hexadecimal x and X notation The letters abcdef are used for x conversions the letters ABCDEF are used for X conversions The precision if any gives the mini mum number of digits that must appear if the converted value requires fewer digits it is padded on the left with zeros e p The void x argument is taken as an unsigned integer and converted similarly as a x command would do Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities 39 e c The int argument is converted to an unsigned char and the resulting character is written e s The char x argument is expected to be a pointer to an array of character type pointer to a string Characters from the array are written up to but not including a terminating NUL character if a precision is specified no more than the number specified are written If a precision is given no null character need be present if the precision is not specified or is greater than the si
113. for avr libc by Doxygen 5 9 Integer Types 22 5 9 2 Typedef Documentation 5 9 2 1 typedef int int16_t 16 bit signed type 5 9 2 2 typedef long int32_t 32 bit signed type 5 9 2 3 typedef long long int64_t 64 bit signed type 5 9 2 4 typedef signed char int8_t 8 bit signed type 5 9 2 5 typedef int16_t intptr_t Signed pointer compatible type 5 9 2 6 typedef unsigned int uint16_t 16 bit unsigned type 5 9 2 7 typedef unsigned long uint32_t 32 bit unsigned type 5 9 2 8 typedef unsigned long long uint64_t 64 bit unsigned type 5 9 2 9 typedef unsigned char uint8_t 8 bit unsigned type 5 9 2 10 typedef uint16_t uintptr_t Unsigned pointer compatible type Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 10 Mathematics 23 5 10 Mathematics 5 10 1 Detailed Description include lt math h gt This header file declares basic mathematics constants and functions Note In order to access the functions delcared herein it is usually also required to addi tionally link against the library 1 ibm a See also the related FAQ entry Defines e define MPI 3 141592653589793238462643 e define M_SQRT2 1 4142135623730950488016887 Functions double cos double _x _ATTR CONST__ double fabs double __x _ATTR_CONST__ double fmod double __x double __y _ATTR_CONST__ double modf double __value double _ ptr double sin double _x _ATTR_CONST_ double sqrt double __x _ATTR C
114. from using 03 Back to FAQ Index 7 3 18 How do I relocate code to a fixed address First the code should be put into a new named section This is done with a section attribute __attribute__ section bootloader In this example boot loader is the name of the new section This attribute needs to be placed after the prototype of any function to force the function into the new section void boot void __attribute__ section bootloader To relocate the section to a fixed address the linker flag section start is used This option can be passed to the linker using the W1 compiler option W1 section start bootloader 0x1E000 The name after section start is the name of the section to be relocated The number after the section name is the beginning address of the named section Back to FAQ Index Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 89 7 3 19 My UART is generating nonsense My ATmega128 keeps crashing Port F is completely broken Well certain odd problems arise out of the situation that the AVR devices as shipped by Atmel often come with a default fuse bit configuration that doesn t match the user s expectations Here is a list of things to care for e All devices that have an internal RC oscillator ship with the fuse enabled that causes the device to run off this oscillator instead of an external crystal This often remains unnot
115. g The strrev function reverses the order of the string Returns The strrev function returns a pointer to the beginning of the reversed string 5 14 2 23 char x strstr const char x s1 const char s2 Locate a substring The strstr function finds the first occurrence of the substring s2 in the string s1 The terminating 10 characters are not compared Returns The strstr function returns a pointer to the beginning of the substring or NULL 1f the substring is not found If s2 points to a string of zero length the function returns sl 5 14 2 24 char x strupr char x string Convert a string to upper case The strupr function will convert a string to upper case Only the lower case alphabetic characters a z are converted Non alphabetic characters will not be changed Returns The strupr function returns a pointer to the converted string The pointer is the same as that passed in since the operation is perform in place Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 15 Interrupts and Signals 5 15 Interrupts and Signals 5 15 1 Detailed Description Note This discussion of interrupts and signals was taken from Rich Neswold s docu ment See Acknowledgments It s nearly impossible to find compilers that agree on how to handle interrupt code Since the C language tries to stay away from machine dependent details each compiler writer is forced to design their method of support
116. grams 69 Denis Chertykov and Marek Michalkiewicz marekm linux org pl for developing the standard libraries and startup code for AVR GCC Uros Platise for developing the AVR programmer tool uisp Joerg Wunsch joerg FreeBSD ORG for adding all the AVR development tools to the FreeBSD http www freebsd org ports tree and for pro viding the basics for the demo project Brian Dean bsd bsdhome com for developing avrdude an alternative to uisp and for contributing documentation which describes how to use it Avr dude was previously called avrprog Eric Weddington eric umginc net for maintaining the WinAVR pack age and thus making the continued improvements to the Opensource AVR toolchain available to many users Rich Neswold for writing the original avr tools document which he graciously allowed to be merged into this document and his improvements to the demo project All the people who have submitted suggestions patches and bug reports See the AUTHORS files of the various tools And lastly all the users who use the software If nobody used the software we would probably not be very motivated to continue to develop it Keep those bug reports coming 7 2 avr libc and assembler programs 7 2 1 Introduction There might be several reasons to write code for AVR microcontrollers using plain assembler source code Among them are Code for devices that do not have RAM and are thus not supported by
117. h an arbitrary amount of white space as determined by iss pace followed by a single optional or sign If base is zero or 16 the string may then include a 0x prefix and the number will be read in base 16 otherwise a zero base is taken as 10 decimal unless the next character is 0 in which case it is taken as 8 octal The remainder of the string is converted to an unsigned long value in the obvious manner stopping at the first character which is not a valid digit in the given base In bases above 10 the letter A in either upper or lower case represents 10 B represents 11 and so forth with Z representing 35 If endptr is not NULL strtoul stores the address of the first invalid character in endpt r If there were no digits at all however strtoul stores the original value of nptr in endptr Thus if xnptr is not 0 but xxendptr is 0 on return the entire string was valid The strtoul function return either the result of the conversion or if there was a lead ing minus sign the negation of the result of the conversion unless the original non Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 14 Strings 51 negated value would overflow in the latter case strtoul returns ULONG_MAX and errno is set to ERANGE If no conversion could be performed 0 is returned 5 13 4 27 char ultoa unsigned long int __val char x _s int _radix The fun
118. he TEMP register data of an in progress transaction that has just started elsewhere To protect interrupt routines against other interrupt routines it s usually best to use the Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions SIGNAL macro when declaring the interrupt function and to ensure that interrupts are still disabled when accessing those 16 bit timer registers Within the main program access to those registers could be encapsulated in calls to the cliQ and sei macros If the status of the global interrupt flag before accessing one of those registers is uncertain something like the following example code can be used uint16_t read_timerl void uint8_t sreg uint16_t val sreg SREG cli val TCNT1 SREG sreg return val Back to FAQ Index 7 3 10 How do I use a define d constant in an asm statement So you tried this asm volatile sbi 0x18 0x07 Which works When you do the same thing but replace the address of the port by its macro name like this asm volatile sbi PORTB 0x07 you get a compilation error Error constant value required PORTB is a precompiler definition included in the processor specific file included in avr io h As you may know the precompiler will not touch strings and PORTB instead of 0x18 gets passed to the assembler One way to avoid this problem is asm volatile sbi 0 0x07 I PORTB
119. he constraint string Using digit n tells the compiler to use the same register as for the n th operand starting with zero Here is an example asm volatile swap 30 r value 0 value This statement will swap the nibbles of an 8 bit variable named value Constraint 0 tells the compiler to use the same input register as for the first operand Note however that this doesn t automatically imply the reverse case The compiler may choose the same registers for input and output even if not told to do so This is not a problem in most cases but may be fatal if the output operator is modified by the assembler code before the input operator is used In the situation where your code depends on different registers used for input and output operands you must add the amp constraint modifier to your output operand The following example demonstrates this problem asm volatile in 0 1 NANE Tout Sl 327 imc amp r input I port r output In this example an input value is read from a port and then an output value is written to the same port If the compiler would have choosen the same register for input and out put then the output value would have been destroyed on the first assembler instruction Fortunately this example uses the amp constraint modifier to instruct the compiler not to select any register for the output value which is used for any of the input operands Back to swapping Here is the code to swap
120. his is currently a FreeBSD only program although adaptation to other systems should not be hard Note It has been ported to windows via cygwin and linux Other unix systems should be trivial to port to avrdude is part of the FreeBSD ports system To install it simply do the following cd usr ports devel avrdude make install Note Installation into the default location usually requires root permissions However running the program only requires access permissions to the appropriate ppi 4 device Building and installing on other systems should use the configure system as such gunzip c avrdude lt version gt tar gz tar xf cd avrdude lt version gt mkdir obj avr cd obj avr configure prefix PREFIX make make install nnnnnnn wn 7 7 8 GDB for the AVR target Gdb also uses the configure system so to build and install bunzip2 c gdb lt version gt tar bz2 tar xf cd gdb lt version gt mkdir obj avr cd obj avr configure prefix PREFIX target avr make make install Ur Tr Ur A A wn Note If you are planning on using avr gdb you will probably want to install either simulavr or avarice since avr gdb needs one of these to run as a a remote target Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 8 Using the avrdude program 118 7 7 9 Simulavr Simulavr also uses the configure system so to build and install gunzip c simulavr lt version gt tar gz ta
121. ibed how such constant data can be moved out to flash ROM How ever a constant string located in flash ROM is no longer a valid argument to pass to a function that expects a const char x type string since the AVR processor needs the special instruction LPM to access these strings Thus separate functions are needed that take this into account Many of the standard C library functions have equivalents available where one of the string arguments can be located in flash ROM Private func tions in the applications need to handle this too For example the following can be used to implement simple debugging messages that will be sent through a UART include lt inttypes h gt Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 90 include lt avr io h gt include lt avr pgmspace h gt void uart_putchar char c if c n uart_putchar r loop_until_bit_is_set USR UDRE UDR c void debug_P const char addr char Gi while c __lpm_inline unsigned short addr uart_putchar c int main void debug_P PSTR foo was here n return 0 Note By convention the suffix _P to the function name is used as an indication that this function is going to accept a program space string Note also the use of the PSTRO macro Back to FAQ Index 7 3 21 Why does the compiler compile an 8 bit operation that uses bitwise oper ators i
122. iced until the first attempt is made to use something critical in timing like UART communication e The ATmegal28 ships with the fuse enabled that turns this device into AT megal03 compatibility mode This means that some ports are not fully usable and in particular that the internal SRAM is located at lower addresses Since by default the stack is located at the top of internal SRAM a program compiled for an ATmega128 running on such a device will immediately crash upon the first function call or rather upon the first function return Devices with a JTAG interface have the JTAGEN fuse programmed by default This will make the respective port pins that are used for the JTAG interface un available for regular IO Back to FAQ Index 7 3 20 Why do all my foo bar strings eat up the SRAM By default all strings are handled as all other initialized variables they occupy RAM even though the compiler might warn you when it detects write attempts to these RAM locations and occupy the same amount of flash ROM so they can be initialized to the actual string by startup code The compiler can optimize multiple identical strings into a single one but obviously only for one compilation unit i e a single C source file That way any string literal will be a valid argument to any C function that expects a const char x argument Of course this is going to waste a lot of SRAM In Program Space String Utilities a method is descr
123. id not support C Note The stdc libs are not included with C for AVR due to the size limitations of the devices Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 7 Installing the GNU Tool Chain 116 7 7 5 AVR Libc Warning You must install avr binutils avr gcc and make sure your path is set properly before installing avr libc Note If you have obtained the latest avr libc from cvs you will have to run the reconf script before using either of the build methods described below To build and install avr libc gunzip c avr libc lt version gt tar gz cd avr libc lt version gt doconf domake cd build make install nnnnn WH Note The doconf script will automatically use the PREF IX environment variable if you have set and exported it Alternatively you could do this shown for consistency with binutils and gcc gunzip c avr libc lt version gt tar gz tar xf cd avr libc lt version gt mkdir obj avr cd obj avr configure prefix PREFIX make make install V UV 117 0 147 Ur Vr 7 7 6 UISP Uisp also uses the configure system so to build and install gunzip c uisp lt version gt tar gz tar xf cd uisp lt version gt mkdir obj avr cd obj avr configure prefix PREFIX make make install UN 17 A UF o UY Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 7 Installing the GNU Tool Chain 117 7 7 7 Avrdude Note T
124. ify the EEPROM segment we can generate a hex file that can be used to program the EEPROM avr objcopy j eeprom change section Ima eeprom 0 O ihex demo elf demo_eeprom hex The resulting demo_eeprom hex file contains 00000001FF which is an empty hex file which is expected since we didn t define any EEPROM variables 7 10 7 Make Build the Project Rather than type these commands over and over they can all be placed in a make file To build the demo project using make save the following in a file called Makefile Note This Makefile can only be used as input for the GNU version of make Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 10 A simple project 139 PRG demo OBJ demo o MCU_TARGET at90s2313 OPTIMIZE 02 DEFS LIBS You should not have to change anything below here CC avr gcc Override is only needed by avr lib build system override CFLAGS g Wall OPTIMIZE mmcu MCU_TARGET DEFS override LDFLAGS W1 Map PRG map OBJCOPY avr objcopy OBJDUMP avr objdump all PRG elf lst text eeprom S PRG elf 0BJ CC CFLAGS LDFLAGS o LIBS clean rm rf o S PRG elf eps png pdf bak rm rf lst map EXTRA_CLEAN_FILES lst S PRG lst lst elf OBJDUMP h S lt gt Rules for building the text rom images text hex bin srec hex PRG hex bin PRG bin srec PRG srec hex
125. in a variable since the datasheet only guarantees the TWSR register to have valid contents while the TWINT bit in TWCR is set ey uint8_t twst Do all the startup time peripheral initializations UART for our debug test output and TWI clock void ioinit void UCSRB _BV TXEN tx enable UBRR SYSCLK 16 9600UL 1 9600 Bd initialize TWI clock 100 kHz clock TWPS 0 gt prescaler 1 if defined TWPS0O has prescaler megal28 amp newer TWSR 0 endif TWBR SYSCLK 100000UL 16 2 Note 4 Send character c down the UART Tx wait until tx holding register is empty EY int Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI 144 uart_putchar char c LE co SS An uart_putchar r loop_until_bit_is_set UCSRA UDRE UDR c return 0 Note 5 Read len bytes from EEPROM starting at eeaddr into buf This requires two bus cycles during the first cycle the device will be selected master transmitter mode and the address transfered Address bits exceeding 256 are transfered in the E2 E1 E0 bits subaddress bits of the device selector The second bus cycle will reselect the device repeated start condition going into master receiver mode and transfer the data from the device to the TWI master Multiple bytes can be transfered by ACKing the client
126. ing overwritten by each other The standard RAM layout is to place data variables first from the beginning of the internal RAM followed by bss The stack is started from the top of internal RAM growing downwards The so called heap available for the dynamic memory allocator will be placed beyond the end of bss Thus there s no risk that dynamic memory will ever collide with the RAM variables unless there were bugs in the implementation of the allocator There is still a risk that the heap and stack could collide if there are large requirements for either dynamic memory or stack space The former can even happen 1f the allocations aren t all that large but dynamic memory allocations get fragmented over time such that new requests don t quite fit into the holes of previously freed regions Large stack space requirements can arise in a C function containing large and or numerous local variables or when recursively calling function Note The pictures shown in this document represent typical situations where the RAM locations refer to an ATmega128 The memory addresses used are not displayed in a linear scale Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 5 Using malloc 104 external RAM 0x1100 OxFFFF on board RAM LI 1 gt SP t RAMEND brkval lt SP __malloc_margin hk __malloc_heap_start __heap_start _ bss end __data_end __bss_start
127. into the assembler listing in file foo 1st when compiling foo c the following compiler command line can be used avr gcc c O foo c o foo o Wa ahls f00 lst In order to pass an assembler file through the C preprocessor first and have the assem bler generate line number debugging information for it the following command can be used avr gcc c x assembler with cpp o foo o foo S Wa gstabs Note that on Unix systems that have case distinguishing file systems specifying a file name with the suffix S upper case letter S will make the compiler automatically assume x assembler with cpp while using s would pass the file directly to the assembler no preprocessing done 7 9 3 Controlling the linker avr Id 7 9 3 1 Selected linker options While there are no machine specific options for avr ld a number of the standard options might be of interest to AVR users e lname Locate the archive library named libname a and use it to resolve currently unresolved symbols from it The library is searched along a path that con sists of builtin pathname entries that have been specified at compile time e g usr local avr lib on Unix systems possibly extended by path name entries as specified by L options that must precede the 1 options on the command line e Lpath Additional location to look for archive libraries requested by 1 options e defsym symbol expr Define a global symbol symbol using expr
128. ion of code in the fini9 gt finil sections 7 6 8 Using Sections in Assembler Code Example include lt avr io h gt section initl ax fprogbits ldi r0 Oxff out _SFR_IO_ADDR PORTB r0 out _SFR_IO_ADDR DDRB ro Note The ax progbits tells the assembler that the section is allocatable a executable x and contains data Qprogbits For more detailed information on the section directive see the gas user manual 7 6 9 Using Sections in C Code Example include lt avr io h gt void my_init_portb void __attribute__ naked __attribute__ section init1 void my_init_portb void outb PORTB Oxff outb DDRB Oxff Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 7 Installing the GNU Tool Chain 112 7 7 Installing the GNU Tool Chain Note This discussion was taken directly from Rich Neswold s document See Ac knowledgments Note This discussion is Unix specific FIXME troth 2002 08 13 we need a volunteer to add windows specific notes to these instructions This chapter shows how to build and install a complete development environment for the AVR processors using the GNU toolset The default behaviour for most of these tools is to install every thing under the usr local directory In order to keep the AVR tools separate from the base system it is usually better to install everything into usr local avr If the usr local a
129. is available on your operating system When it finishes it will have created several Makefiles that are custom tailored to your platform At this point you can build the project make Note BSD users should note that the project s Makefile uses GNU make syntax This means FreeBSD users may need to build the tools by using gmake If the tools compiled cleanly you re ready to install them If you specified a destination that isn t owned by your account you ll need root access to install them To install make install You should now have the programs from binutils installed into SPREFIX bin Don t forget to set your PATH environment variable before going to build avr gcc 7 7 4 GCC for the AVR target Warning You must install avr binutils and make sure your path is set properly before in stalling avr gcc The steps to build avr gcc are essentially same as for binutils bunzip2 c gcc lt version gt tar bz2 tar xf cd gcc lt version gt mkdir obj avr cd obj avr Ur Ar 107 Ur wn configure prefix PREFIX target avr enable languages c ct disable nls make make install Ur To save your self some download time you can alternatively download only the gcc core lt version gt tar bz2 and gcc c lt version gt tar bz2 parts of the gcc Also if you don t need C support you only need the core part and should only enable the C language support Note Early versions of these tools d
130. is is done using the GNU assembler option gstabs Example Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 81 avr as mmcu atmegal28 gstabs o foo o foo s When the assembler is not called directly but through the C compiler frontend either implicitly by passing a source file ending in S or explicitly using x assembler with cpp the compiler frontend needs to be told to pass the gstabs option down to the assembler This is done using Wa gstabs Please take care to only pass this option when compiling an assembler input file Oth erwise the assembler code that results from the C compilation stage will also get line number information which confuses the debugger Note You can also use Wa gstabs since the compiler will add the extra for you Example EXTRA_OPTS Wall mmcu atmegal28 x assembler with cpp avr gcc Wa gstabs EXTRA_OPTS c o foo o foo S Also note that the debugger might get confused when entering a piece of code that has a non local label before since it then takes this label as the name of a new function that appears to have been entered Thus the best practice to avoid this confusion is to only use non local labels when declaring a new function and restrict anything else to local labels Local labels consist just of a number only References to these labels consist of the number followed by the letter b for a backwa
131. is no actual file implementation available so only device IO can be performed Since there s no operating system the application needs to provide enough details about their devices in order to make them usable by the standard IO facilities Due to space constraints some functionality has not been implemented at all like some of the printf conversions that have been left out Nevertheless potential users of this implementation should be warned the printf and scanf families of functions although usually associated with presumably simple things like the famous Hello world program are actually fairly complex which causes their inclusion to eat up a fair amount of code space Also they are not fast due to the nature of interpreting the format string at run time Whenever possible resorting to the sometimes non standard predetermined conversion facilities that are offered by avr libc will usually cost much less in terms of speed and code size In order to allow programmers a code size vs functionality tradeoff the function vfprintf which is the heart of the printf family can be selected in different flavours using linker options See the documentation of vfprintf for a detailed description The same applies to vfscanf and the scanf family of functions The standard streams stdin stdout and stderr are provided but contrary to the C standard since avr libc has no knowledge about applicable devices these streams are not alre
132. ith this stuff If we meet some day and you think this stuff is worth it you can buy me a beer in return Joerg Wunsch Simple AVR demonstration Controls a LED that can be directly connected from OC1 OC1A to GND The brightness of the LED is controlled with the PWM After each period of the PWM the PWM value is either incremented or decremented that s all SId demo c v 1 1 2002 09 30 18 16 07 troth Exp E ee E E E include lt inttypes h gt include lt avr io h gt include lt avr interrupt h gt include lt avr signal h gt if defined __AVR_AT90S2313__ define OCI PB3 define OCR OCR1 define DDROC DDRB elif defined __AVR_AT90S2333__ defined __AVR_AT90S4433__ define OCI PB1 define DDROC DDRB define OCR OCR1 elif defined __AVR_AT90S4414_ defined __AVR_AT90S4434_ defined __AVR_ATmegal63__ define OCI PD5 define DDROC DDRD define OCR OCRIA else error Don t know what kind of MCU you are compiling for endif I defined __AVR_AT90S8515__ A I defined __AVR_AT90S8535_ Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 10 A simple project 131 if defined COM11 define XCOM11 COM11 elif defined COM1A1 define XCOM11 COM1A1 else error need either COM1A1 or COM11 endif enum UP DOWN volatile uint16_t pwm Note 1 volatile uint8_t direction SIGNAL SIG_OVERFLOW1 Note 2 s
133. k and heap are separated in distinct memory areas this is the safest way to avoid a stack heap collision 7 5 3 Tunables for malloc There are a number of variables that can be tuned to adapt the behavior of malloc to the expected requirements and constraints of the application Any changes to these Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 5 Using malloc 105 tunables should be made before the very first call to malloc Note that some library functions might also use dynamic memory notably those from the Standard IO facili ties so make sure the changes will be done early enough in the startup sequence The variables _malloc_heap_start and _malloc_heap_end can be used to re strict the malloc function to a certain memory region These variables are statically initialized to point to _heap_start and _heap_end respectively where _heap_ start is filled in by the linker to point just beyond bss and _heap_end is set to 0 which makes malloc assume the heap is below the stack If the heap is going to be moved to external RAM _malloc_heap_end must be adjusted accordingly This can either be done at run time by writing directly to this variable or it can be done automatically at link time by adjusting the value of the symbol _heap_end The following example shows a linker command to relocate the entire data and bss segments and the heap to location 0x1100 in external RAM The heap will exte
134. le TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_MR_DATA_NACK len 0 force end of loop FALLTHROUGH case TW_MR_DATA_ACK buf TWDR rv break default goto error quit Note 12 TWCR _BV TWINT _BV TWSTO _BV TWEN send stop condition return rv Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI 147 error rv 1 goto quit Write len bytes into EEPROM starting at eeaddr from buf This is a bit simpler than the previous function since both the address and the data bytes will be transfered in master transmitter mode thus no reselection of the device is necessary However the EEPROMs are only capable of writing one page simultaneously so care must be taken to not cross a page boundary within one write cycle The amount of data one page consists of varies from manufacturer to manufacturer some vendors only use 8 byte pages for the smaller devices and 16 byte pages for the larger devices while other vendors generally use 16 byte pages We thus use the smallest common denominator of 8 bytes per page declared by the macro PAGE_SIZE above The function simply returns after writing one page returning the actual number of data byte written It is up to the caller to re invoke it in order to write further data int ee24xx_write_page uint16_
135. lly the generic documentation of these tools is fairly large and maintained in texinfo files Command line options are explained in detail in the manual page 7 9 1 Options for the C compiler avr gcc 7 9 1 1 Machine specific options for the AVR The following machine specific op tions are recognized by the C compiler frontend e mmcu architecture Compile code for architecture Currently known architectures are Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 9 Using the GNU tools 121 cluding the file lt avr io h gt cannot work since it cannot decide which de vice s definitions to select e mmcu MCU type The following MCU types are currently understood by avr gcc matches them against the corresponding avr gcc architecture name and shows avrl Simple CPU core only assembler support avr2 Classic CPU core up to 8 KB of ROM avr3 Classic CPU core more than 8 KB of ROM avr4 Enhanced CPU core up to 8 KB of ROM avr5 Enhanced CPU core more than 8 KB of ROM By default code is generated for the avr2 architecture Note that when only using mmcu architecture but no mmcu MCU type in the preprocessor symbol declared by the mmcu option Architecture MCU name Macro avrl at90s1200 _ AVR_AT90S 1200__ avrl attiny11 _ AVR_ATtiny11__ avrl attiny 12 AVR_ATtiny12__
136. ls which extract data from object files avr objcopy dissassem ble object file information avr objdump and strip information from object files avr strip Before we can build the C compiler these tools need to be in place Download and unpack the source files bunzip2 c binutils lt version gt tar bz2 tar xf cd binutils lt version gt Note Replace lt version gt with the version of the package you downloaded Note If you obtained a gzip compressed file gz use gunzip instead of bunzip2 It is usually a good idea to configure and build binutils in a subdirectory so as not to pollute the source with the compiled files This is recommended by the binutils developers mkdir obj avr cd obj avr The next step is to configure and build the tools This is done by supplying arguments to the configure script that enable the AVR specific options configure prefix PREFIX target avr disable nls If you don t specify the prefix option the tools will get installed in the usr local hierarchy i e the binaries will get installed in usr local bin the info pages get installed in usr local info etc Since these tools are chang ing frequently It is preferrable to put them in a location that is easily removed Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 7 Installing the GNU Tool Chain 115 When configure is run it generates a lot of messages while it determines what
137. m memory 5 12 3 16 size_t fwrite const void _ ptr size_t _size size_t _nmemb FILE x _stream Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities 36 Write nmemb objects size bytes each to stream The first byte of the first object is referenced by ptr Returns the number of objects successfully written i e nmemb unless an output error occured 5 12 3 17 char gets char x _ str Similar to fgets except that it will operate on stream st din and the trailing newline if any will not be stored in the string It is the caller s responsibility to provide enough storage to hold the characters read 5 12 3 18 int printf const char x __fmt The function printf performs formatted output to stream stderr See vfprintf for details 5 12 3 19 int printf P const char x __fmt Variant of printf that uses a fmt string that resides in program memory 5 12 3 20 int puts const char x __str Write the string pointed to by str and a trailing newline character to stdout 5 12 3 21 int puts_P const char x __str Variant of puts where st r resides in program memory 5 12 3 22 int scanf const char _ fmt The function scanf performs formatted input from stream stdin See vfscanf for details 5 12 3 23 int scanf_P const char _fmt Variant of scanf where fmt resides in program memory 5 12 3 24 int snprintf char x _s size_t _n
138. math 25 sinh avr_math 25 sleep_mode avr_sleep 14 SLEEP_MODE_ADC avr_sleep 13 SLEEP_MODE_EXT_STANDBY avr_sleep 13 SLEEP_MODE_IDLE avr_sleep 13 SLEEP_MODE_PWR_DOWN avr_sleep 14 SLEEP_MODE_PWR_SAVE avr_sleep 14 SLEEP_MODE_STANDBY avr_sleep 14 snprintf avr_stdio 35 snprintf_P avr_stdio 35 Special function registers 62 sprintf avr_stdio 36 sprintf_P avr_stdio 36 sqrt avr_math 25 square avr_math 25 srand avr_stdlib 48 srandom avr_stdlib 48 sscanf avr_stdio 36 sscanf_P avr_stdio 36 Standard IO facilities 28 stderr avr_stdio 32 stdin avr_stdio 32 stdout avr_stdio 32 strcasecmp avr_string 53 strcasecmp_P avr_pgmspace 9 strcat avr_string 53 strcat_P avr_pgmspace 9 strchr avr_string 53 strcmp avr_string 54 stremp_P avr_pgmspace 10 strcpy avr string 54 strcpy_P avr_pgmspace 10 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen INDEX 161 Strings 50 tanh strlcat avr_math 26 avr_string 54 timer_enable_int strlcpy avr_interrupts 62 avr_string 55 toascii strlen ctype 18 avr_string 55 tolower strlen_P ctype 19 avr_pgmspace 10 strlwr avr_string 55 strncasecmp avr_string 55 strncasecmp_P avr_pgmspace 10 strncat avr_string 55 strncmp avr_string 56 strnemp_P avr_pgmspace 11 strncpy avr_string 56 strncpy_P avr_pgmspace 11 strnlen avr_string 56 strrchr avr_string 56 strrev avr_string 57 strstr
139. mbled e mno skip bug Don t emit a warning when trying to skip a 2 word instruction with a CPSE SBIC SBIS SBRC SBRS instruction Early AVR devices suffered from a hardware bug where these instructions could not be properly skipped e mno wrap For RJMP RCALL instructions don t allow the target address to wrap around for devices that have more than 8 KB of memory e gstabs Generate stabs debugging symbols for assembler source lines This enables avr gdb to trace through assembler source files This option must not be used when assembling sources that have been generated by the C compiler these files already contain the appropriate line number information from the C source files e a cdhlmns file Turn on the assembler listing The sub options are c omit false conditionals d omit debugging directives h include high level source 1 include assembly minclude macro expansions n omit forms processing s include symbols file set the name of the listing file The various sub options can be combined into a single a option list file must be the last one in that case Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 9 Using the GNU tools 126 7 9 2 2 Examples for assembler options passed through the C compiler Re member that assembler options can be passed from the C compiler frontend using Wa see above so in order to include the C source code
140. most up to date and detailed information on contraints for the avr can be found in the gcc manual Note The x register is r27 r26 the y register is r29 r28 and the z register is r3 hir30 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 4 Inline Asm 95 Constraint Used for Range a Simple upper registers rl6 to r23 b Base pointer registers y Z pairs d Upper register rl6tor31 e Pointer register pairs X y Z G Floating point constant 0 0 I 6 bit positive integer 0 to 63 constant J 6 bit negative integer 63 to 0 constant K Integer constant 2 L Integer constant 0 1 Lower registers rO to r15 M 8 bit integer constant 0 to 255 N Integer constant 1 O Integer constant 8 16 24 P Integer constant 1 q Stack pointer register SPH SPL r Any register rO to 131 t Temporary register r0 W Special upper register 124 r26 r28 r30 pairs x Pointer register pair X X 127 126 y Pointer register pair Y y 129 128 Z Pointer register pair Z z r31 r30 These definitions seem not to fit properly to the AVR instruction set The author s as sumption is that this part of the compiler has never been really finished in this version but that assumption may be wrong The selection of the proper contraint depends on the range of the constants or registers which must be acceptable to the AVR instruction they are used with The C c
141. ncpy function is similar to strcpy except that not more than n bytes of src are copied Thus if there is no null byte among the first n bytes of src the result will not be null terminated In the case where the length of src is less than that of n the remainder of dest will be padded with nulls Returns The strncpy function returns a pointer to the destination string dest 5 14 2 20 size_t strnlen const char src size_t len Determine the length of a fixed size string The strnlen function returns the number of characters in the string pointed to by src not including the terminating 0 character but at most len In doing this strnlen looks only at the first len characters at src and never beyond src len Returns The strnlen function returns strlen src if that is less than len or len if there is no 0 character among the first len characters pointed to by src Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 14 Strings 58 5 14 2 21 char x strrchr const char x src int val Locate character in string The strrchr function returns a pointer to the last occurrence of the character val in the string src Here character means byte these functions do not work with wide or multi byte characters Returns The strrchr function returns a pointer to the matched character or NULL if the character is not found 5 14 2 22 char x strrev char string Reverse a strin
142. nd up to address Oxffff avr gcc W1 Tdata 0x801100 defsym __heap_end 0x80ffff Note See explanation for offset 0x800000 See the chapter about using gcc for the W1 options S ES te 5 amp S on board RAM z x external RAM L o 6 6 6 SP 1 _ _malloc_heap_end __heap_end RAMEND Eo __malloc_heap_start __heap_start __bss_end __data_en _ bss_ start data start Figure 2 Internal RAM stack only external RAM variables and heap If dynamic memory should be placed in external RAM while keeping the variables in internal RAM something like the following could be used Note that for demonstration purposes the assignment of the various regions has not been made adjacent in this example so there are holes below and above the heap in external RAM that remain completely unaccessible by regular variables or dynamic memory allocations shown in light bisque color in the picture below Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 5 Using malloc 106 avr gcc Wl defsym __heap_start 0x802000 defsym __heap_end 0x803fff giga RAM Mu 0x0100 Ox10FF 0x1100 0x2000 Ox3FFF OxFFFF on board RAM et __malloc_heap_end __heap_end et brkval _ bss end __malloc_heap_start __heap_start _ data_end __bss start data start Figure 3 Internal RAM variables and stack external RAM heap If _malloc_heap_endis 0 the allocator attemp
143. nd_r 47 WDTO_500MS 16 random 47 WDTO_60MS 16 RANDOM_MAX 43 random r 48 srand 48 srandom 48 strtod 48 strtol 48 strtoul 49 ultoa 50 utoa 50 avr_string memccpy 51 avrdude usage 117 avrprog usage 117 bit_is_clear avr_sfr 64 bit_is_set avr_sfr 64 bsearch avr_stdlib 44 BV avr_sfr 65 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen INDEX 157 calloc avr_stdlib 45 avr_stdlib 45 cbi EDOM avr_sfr 65 avr_errno 19 ceil EEPROM handling 4 avr_math 23 Character Operations 16 clearerr avr_stdio 32 cli avr interrupts 61 cos avr_math 23 cosh avr_math 23 ctype isalnum 17 isalpha 17 isascii 17 isblank 17 iscntrl 17 isdigit 18 isgraph 18 islower 18 isprint 18 ispunct 18 isspace 18 isupper 18 isxdigit 18 toascii 18 tolower 19 toupper 19 disassembling 131 div avr_stdlib 45 div_t 67 DTOSTR_ALWAYS_SIGN avr_stdlib 43 DTOSTR_PLUS_SIGN avr_stdlib 43 DTOSTR_UPPERCASE avr_stdlib 43 dtostre avr_stdlib 45 dtostrf eeprom_is_ready avr_eeprom 5 eeprom_rb avr_eeprom 5 eeprom_read_block avr_eeprom 6 eeprom_read_byte avr_eeprom 6 eeprom_read_word avr_eeprom 6 eeprom_rw avr_eeprom 6 eeprom_wb avr_eeprom 6 eeprom_write_byte avr_eeprom 6 enable_external_int avr_interrupts 62 EOF avr_stdio 31 ERANGE avr_errno 19 exit avr_stdlib 45 exp avr_math 24 fabs avr_math 24 FAQ 72 fclose avr_st
144. ne the part of a compiler listing which may have been generated from our example lds r24 value APP in r24 12 NOAPP sts value r24 The comments have been added by the compiler to inform the assembler that the in cluded code was not generated by the compilation of C statements but by inline as sembler statements The compiler selected register r24 for storage of the value read from PORTD The compiler could have selected any other register though It may not explicitely load or store the value and it may even decide not to include your assembler code at all All these decisions are part of the compiler s optimization strategy For example if you never use the variable value in the remaining part of the C program the compiler will most likely remove your code unless you switched off optimization To avoid this you can add the volatile attribute to the asm statement asm volatile in 0 1 r value I PORTD The last part of the asm instruction the clobber list is mainly used to tell the compiler about modifications done by the assembler code This part may be omitted all other parts are required but may be left empty If your assembler routine won t use any input or output operand two colons must still follow the assembler code string A good example is a simple statement to disable interrupts asm volatile cli Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 4 Inline Asm 9
145. ng malloc The amount of stack required for your application cannot be determined that easily For example if you recursively call a function and forget to break that recursion the amount of stack required is infinite You can look at the generated assembler code avr gcc S there s a comment in each generated assembler file that tells you the frame size for each generated function That s the amount of stack required for this function you have to add up that for all functions where you know that the calls could be nested Back to FAQ Index 7 4 Inline Asm AVR GCC Inline Assembler Cookbook About this Document The GNU C compiler for Atmel AVR RISC processors offers to embed assembly language code into C programs This cool feature may be used for manually optimizing time critical parts of the software or to use specific processor instruction which are not available in the C language Because of a lack of documentation especially for the AVR version of the compiler it may take some time to figure out the implementation details by studying the compiler and assembler source code There are also a few sample programs available in the net Hopefully this document will help to increase their number It s assumed that you are familiar with writing AVR assembler programs because this is not an AVR assembler programming tutorial It s not a C language tutorial either Generated on Tue Apr 22 09 54 12 2003 for avr libc
146. nt fclose FILE x _ stream This function closes st ream and disallows and further IO to and from it It currently always returns 0 for success 5 12 3 3 FILE fdevopen int put char int get void int opts _attribute__ unused This function is a replacement for fopen It opens a stream for a device where the actual device implementation needs to be provided by the application If successful a pointer to the structure for the opened stream is returned Reasons for a possible failure currently include that neither the Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities 34 put nor the get argument have been provided thus attempting to open a stream with no IO intent at all or that insufficient dynamic memory is available to establish a new stream If the put function pointer is provided the stream is opened with write intent The function passed as put shall take one character to write to the device as argument and shall return 0 if the output was successful and a nonzero value if the character could not be sent to the device If the get function pointer is provided the stream is opened with read intent The function passed as get shall take no arguments and return one character from the device passed as an int type If an error occurs when trying to read from the device it shall return 1 If both functions are provided the stream is opened with read and
147. nterface to some simple library routines suitable for han dling the data EEPROM contained in the AVR microcontrollers The implementation uses a simple polled mode interface Applications that require interrupt controlled EEPROM access to ensure that no time will be wasted in spinloops will have to deploy their own implementation Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 1 EEPROM handling Note All of the read write functions first make sure the EEPROM is ready to be ac cessed Since this may cause long delays if a write operation is still pending time critical applications should first poll the EEPROM e g using eeprom_is_ready before attempting any actual I O Note This library will not work with the ATmega169 since this device has the EEPROM IO ports at different locations avr libc declarations define eeprom_is_ready bit_is_clear EECR EEWE uint8_t eeprom_read_byte uint8_t xaddr uint16_t eeprom_read_word uint16_t xaddr void eeprom_write_byte uint8_t addr uint8_t val void eeprom_read_block void buf void addr size_t n Backwards compatibility defines e define eeprom rb addr eeprom_read_byte uint8_t x addr e define eeprom rw addr eeprom read_word uint16_t addr e define eeprom_wb addr val eeprom_write_byte uint8 t addr uint8_ t val IAR C compatibility defines e define EEPUT addr val eeprom_wb addr val e define _EEGET var addr var
148. nto a 16 bit operation in assembly Bitwise operations in Standard C will automatically promote their operands to an int which is by default 16 bits in avr gcc To work around this use typecasts on the operands including literals to declare that the values are to be 8 bit operands This may be especially important when clearing a bit var amp mask wrong way The bitwise not operator will also promote the value in mask to an int To keep it an 8 bit value typecast before the not operator Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 4 Inline Asm var amp unsigned char mask Back to FAQ Index 7 3 22 How to detect RAM memory and variable overlap problems You can simply run avr nm on your output ELF file Run it with the n option and it will sort the symbols numerically by default they are sorted alphabetically Look for the symbol _end that s the first address in RAM that is not allocated by a variable avr gcc internally adds 0x800000 to all data bss variable addresses so please ignore this offset Then the run time initialization code initializes the stack pointer by default to point to the last avaialable address in internal SRAM Thus the region between _end and the end of SRAM is what is available for stack If your application uses malloc which e g also can happen inside printf the heap for dynamic memory is also located there See Usi
149. o force the first character of the output string to a zero except if a zero value is printed with an explicit precision of zero For x and X conversions a non zero result has the string Ox or OX for X conversions prepended to it 0 zero Zero padding For all conversions the converted value is padded on the left with zeros rather than blanks If a precision is given with a numeric conversion d i o u i x and X the 0 flag is ignored A negative field width flag the converted value is to be left adjusted on the field boundary The converted value is padded on the right with blanks rather than on the left with blanks or zeros A overrides a 0 if both are given space A blank should be left before a positive number produced by a signed conversion d or i A sign must always be placed before a number produced by a signed conversion A overrides a space if both are used An optional decimal digit string specifying a minimum field width If the converted value has fewer characters than the field width it will be padded with spaces on the left or right if the left adjust173 ment flag has been given to fill out the field width e An optional precision in the form of a period followed by an optional digit string If the digit string is omitted the precision is taken as zero This gives the minimum number of digits to appear for d i o u x and X conversions or the maximum number o
150. ocal variable to hold a temporary value Another use for a local variable is a return value The following function returns a 16 bit value read from two successive port addresses Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 4 Inline Asm 102 uintl6_t inw uint8_t port uint16_t result asm volatile in SAD SI ot in BO 1 1 r result I port i return result Note inw is supplied by avr libc 7 4 7 C Names Used in Assembler Code By default AVR GCC uses the same symbolic names of functions or variables in C and assembler code You can specify a different name for the assembler code by using a special form of the asm statement unsigned long value asm clock 3686400 This statement instructs the compiler to use the symbol name clock rather than value This makes sense only for external or static variables because local variables do not have symbolic names in the assembler code However local variables may be held in registers With AVR GCC you can specify the use of a specific register void Count void register unsigned char counter asm r3 some code asm volatile clr r3 more code The assembler instruction clr r3 will clear the variable counter AVR GCC will not completely reserve the specified register If the optimizer recognizes that the vari able will not be referenced any longer the register may be re used But the compiler 1s n
151. ompiler doesn t check any line of your assembler code But it is able to check the constraint against your C expression However if you specify the wrong constraints then the compiler may silently pass wrong code to the assem bler And of course the assembler will fail with some cryptic output or internal errors For example if you specify the constraint r and you are using this register with an ori instruction in your assembler code then the compiler may select any register This will fail if the compiler chooses r2 to r15 It will never choose r0 or r1 because these are uses for special purposes That s why the correct constraint in that case is d On the other hand if you use the constraint M the compiler will make sure that you don t pass anything else but an 8 bit value Later on we will see how to pass multibyte expression results to the assembler code The following table shows all AVR assembler mnemonics which require operands and the related contraints Because of the improper constraint definitions in version 3 3 they aren t strict enough There is for example no constraint which restricts integer Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 4 Inline Asm 96 constants to the range 0 to 7 for bit set and bit clear operations Mnemonic Constraints Mnemonic Constraints adc LI ad
152. onst char x PGM_P size_t _ATTR_PURE__ char x strncpy_P char x PGM_P size_t 5 3 2 Define Documentation 5 3 2 1 define PGM_P const prog_char x Used to declare a variable that is a pointer to a string in program space 5 3 2 2 define PGM_VOID_P const prog_void x Used to declare a generic pointer to an object in program space Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 3 Program Space String Utilities 10 5 3 2 3 define PRG_RDB addr _LPM unsigned short addr Read a byte from program space using the 1pm instruction Note The lpm instruction is not available for some AVR devices 5 3 2 4 define PSTR s static char _c PROGMEM s _c Used to declare a static pointer to a string in program space 5 3 3 Function Documentation 5 3 3 1 unsigned char __elpm inline unsigned long _addr static Use this for access to gt 64K program memory ATmegal03 ATmegal28 addr RAMPZ r31 130 Note If possible put your constant tables in the lower 64K and use lpm since it is more efficient that way and you can still use the upper 64K for executable code 5 3 3 2 void x memcpy_P void dest PGM_VOID_P src size_t n The memcpy_P function is similar to memcpy except the src string resides in pro gram space Returns The memcpy_P function returns a pointer to dest 5 3 3 3 int strcasecmp_P const char x s1 PGM_P s2 Compare two strings ignoring case The strcasecm
153. oo map avr gcc 0 o foo out Wl Map foo map Wl cref foo c Alternatively a comma as a placeholder will be replaced by a space before passing the option to the linker So for a device with external SRAM the following command line would cause the linker to place the data segment at address 0x2000 in the SRAM avr gcc mmcu atmegal28 o foo out Wl Tdata 0x802000 See the explanation of the data section for why 0x800000 needs to be added to the ac tual value Note that unless a minit stack option has been given when compiling the C source file that contains the function main the stack will still remain in inter nal RAM through the symbol __st ack that is provided by the run time startup code This is probably a good idea anyway since internal RAM access is faster and even required for some early devices that had hardware bugs preventing them from using a stack in external RAM Note also that the heap for malloc will still be placed after all the variables in the data section so in this situation no stack heap collision can occur 7 10 A simple project At this point you should have the GNU tools configured built and installed on your system In this chapter we present a simple example of using the GNU tools in an AVR project After reading this chapter you should have a better feel as to how the tools are used and how a Makefile can be configured 7 10 1 The Project This project will use the pulse width mo
154. ot able to check wether this register usage conflicts with any predefined register If you reserve too many registers in this way the compiler may even run out of registers during code generation In order to change the name of a function you need a prototype declaration because the compiler will not accept the asm keyword in the function definition Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 5 Using malloc 103 extern long Calc void asm CALCULATE Calling the function Calc will create assembler instructions to call the function CALCULATE 7 4 8 Links For a more thorough discussion of inline assembly usage see the gcc user manual The latest version of the gcc manual is always available here http gcc gnu org onlinedocs 7 5 Using malloc 7 5 1 Introduction On a simple device like a microcontroller implementing dynamic memory allocation 1s quite a challenge Many of the devices that are possible targets of avr libc have a minimal amount of RAM The smallest parts supported by the C environment come with 128 bytes of RAM This needs to be shared between initialized and uninitialized variables sections data and bss the dynamic memory allocator and the stack that is used for calling subroutines and storing local automatic variables Also unlike larger architectures there is no hardware supported memory management which could help in separating the mentioned RAM regions from be
155. p Do not generate tablejump instructions By default jump tables can be used to optimize switch statements When turned off sequences of compare state ments are used instead Jump tables are usually faster to execute on average but in particular for switch statements where most of the jumps would go to the default label they might waste a bit of flash memory mshort calls Use rjmp rcall limited range on gt 8K devices On avr2 and avr4 archi tectures less than 8 KB or flash memory this is always the case On avr3 and avr5 architectures calls and jumps to targets outside the current function will by default use jmp ca1l1 instructions that can cover the entire address range but that require more flash ROM and execution time mrt1 Dump the internal compilation result called RTL into comments in the gener ated assembler code Used for debugging avr gcc msize Dump the address size and relative cost of each statement into comments in the generated assembler code Used for debugging avr gcc mdeb Generate lots of debugging information to stderr 7 9 1 2 Selected general compiler options The following general gcc options might be of some interest to AVR users e On Optimization level n Increasing n is meant to optimize more an optimization level of O means no optimization at all which is the default if no O option is present The special option Os is meant to turn on all 02 optimizations that are not
156. p_P function compares the two strings s1 and s2 ignoring the case of the characters Parameters sI A pointer to a string in the devices SRAM s2 A pointer to a string in the devices Flash Returns The strcasecmp_P function returns an integer less than equal to or greater than zero if sl is found respectively to be less than to match or be greater than s2 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 3 Program Space String Utilities 11 5 3 3 4 char x strcat_P char x dest PGM P src The strcat_P function is similar to strcat except that the src string must be located in program space flash Returns The strcat function returns a pointer to the resulting string dest 5 3 3 5 int stremp_P const char s1 PGM P s2 The stremp_P function is similar to stremp except that s2 is pointer to a string in program space Returns The stremp_P function returns an integer less than equal to or greater than zero if sl is found respectively to be less than to match or be greater than s2 5 3 3 6 char x strepy_P char x dest PGM_P src The strcpy_P function is similar to strcpy except that src is a pointer to a string in program space Returns The strcpy_P function returns a pointer to the destination string dest 5 3 3 7 size_t strlen_P PGM_P src The strlen_P function is similar to strlen except that src is a pointer to a string in program space Returns
157. pt for a variable that keeps track of the lowest memory segment available for reallocation Since both a chain pointer and the size of the chunk need to be recorded in each chunk the minimum chunk size on the freelist is four bytes Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 6 Memory Sections 107 When allocating memory first the freelist is walked to see if it could satisfy the request If there s a chunk available on the freelist that will fit the request exactly it will be taken disconnected from the freelist and returned to the caller If no exact match could be found the closest match that would just satisfy the request will be used The chunk will normally be split up into one to be returned to the caller and another smaller one that will remain on the freelist In case this chunk was only up to two bytes larger than the request the request will simply be altered internally to also account for these additional bytes since no separate freelist entry could be split off in that case If nothing could be found on the freelist heap extension is attempted This is where _malloc_margin will be considered if the heap is operating below the stack or where _malloc_heap end will be verified otherwise If the remaining memory is insufficient to satisfy the request NULL will eventually be returned to the caller When calling free a new freelist entry will be prepared An attempt is then made to aggregate
158. ptional or sign If base is zero or 16 the string may then include a 0x prefix and the number will be read in base 16 otherwise a zero base is taken as 10 decimal unless the next character is 0 in which case it is taken as 8 octal The remainder of the string is converted to a long value in the obvious manner stopping at the first character which is not a valid digit in the given base In bases above 10 the letter A in either upper or lower case represents 10 B represents 11 and so forth with Z representing 35 If endptr is not NULL strtol stores the address of the first invalid character in endptr If there were no digits at all however strtol stores the original value of nptr in endptr Thus if xnptr is not 0 but rendpt r is 0 on return the entire string was valid The strtol function returns the result of the conversion unless the value would under flow or overflow If no conversion could be performed 0 is returned If an overflow or underflow occurs errno is set to ERANGE and the function return value is clamped to LONG_MIN or LONG_MAX respectively 5 13 4 26 unsigned long strtoul const char x _nptr char xx _endptr int _base The strtoul function converts the string in npt r to an unsigned long value The con version is done according to the given base which must be between 2 and 36 inclusive or be the special value 0 The string may begin wit
159. put This function is the heart of the scanf family of functions Characters are read from st ream and processed in a way described by fmt Conver sion results will be assigned to the parameters passed via ap The format string fmt is scanned for conversion specifications Anything that doesn t comprise a conversion specification is taken as text that is matched literally against the input White space in the format string will match any white space in the data including none all other characters match only itself Processing is aborted as soon as the data and format string no longer match or there is an error or end of file condition on stream Most conversions skip leading white space before starting the actual conversion Conversions are introduced with the character Possible options can follow the e a x indicating that the conversion should be performed but the conversion result is to be discarded no parameters will be processed from ap e the character h indicating that the argument is a pointer to short int rather than int e the character 1 indicating that the argument is a pointer to long int rather than int for integer type conversions or a pointer to double for floating point conversions In addition a maximal field width may be specified as a nonzero positive decimal integer which will restrict the conversion to at most this many characters from the input stream This field width is limited to at most 127 ch
160. r safety sts _SFR_ADDR SPMCR r24 In C programs all 3 combinations of _SFR_ASM_COMPAT and __SFR_OFFSET are supported the _ SFR_ADDR SPMCR macro can be used to get the address of the SPMCR register 0x57 or 0x68 depending on device Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 5 Power Management and Sleep Modes 14 The old inp outp macros are still supported but not recommended to use in new code The order of outp arguments is confusing 5 5 Power Management and Sleep Modes 5 5 1 Detailed Description include lt avr sleep h gt Use of the SLEEP instruction can allow your application to reduce it s power com sumption considerably AVR devices can be put into different sleep modes by chang ing the SMn bits of the MCU Control Register MCUCR Refer to the datasheet for the details relating to the device you are using Sleep Modes Note Some of these modes are not available on all devices See the datasheet for target device for the available sleep modes e define SLEEP MODE IDLE 0 e define SLEEP MODE ADC _BV SM0 e define SLEEP MODE PWR DOWN BV SM1 e define SLEEP MODE PWR SAVE _BV SMO BV SM1 e define SLEEP_MODE_STANDBY BV SM1 BV SM2 e define SLEEP_MODE EXT STANDBY BV SMO BV SM1 BV SM2 Sleep Functions e void set_sleep_mode uint8_t mode e void sleep_mode void 5 5 2 Define Documentation 5 5 2 1 define SLEEP MO
161. r xf cd simulavr lt version gt mkdir obj avr cd obj avr configure prefix PREFIX make make install Ur Ur Ur Ur A 49 Ur Note You might want to have already installed avr binutils avr gcc and avr libc if you want to have the test programs built in the simulavr source 7 7 10 AVaRice Note These install notes are specific to avarice 1 5 You will have to edit prog avarice Makefile for avarice in order to install into a directory other than usr local avr bin Edit the line which looks like this INSTALL_DIR usr local avr bin such that INSTALL_DIR is now set to whatever you decided on PREFIX bin to be gunzip c avarice 1 5 tar gz tar xf cd avarice 1 5 prog avarice make make install nnn DW 7 8 Using the avrdude program Note This section was contributed by Brian Dean bsdtbsdhome com Note The avrdude program was previously called avrprog The name was changed to avoid confusion with the avrprog program that Atmel ships with AvrStudio avrdude is a program that is used to update or read the flash and EEPROM memories of Atmel AVR microcontrollers on FreeBSD Unix It supports the Atmel serial pro gramming protocol using the PC s parallel port and can upload either a raw binary file Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 8 Using the avrdude program 119 or an Intel Hex format file It can also be used in an interactive mode to individually update
162. rc size_t len Copy a memory area The memcpy function copies len bytes from memory area src to memory area dest The memory areas may not overlap Use memmove if the memory areas do overlap Returns The memcpy function returns a pointer to dest Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 14 Strings 54 5 14 2 5 void x memmove void x dest const void x src size_t len Copy memory area The memmove function copies len bytes from memory area src to memory area dest The memory areas may overlap Returns The memmove function returns a pointer to dest 5 14 2 6 void x memset void x dest int val size_t len Fill memory with a constant byte The memset function fills the first len bytes of the memory area pointed to by dest with the constant byte val Returns The memset function returns a pointer to the memory area dest 5 14 2 7 int strcasecmp const char x s1 const char x s2 Compare two strings ignoring case The strcasecmp function compares the two strings s1 and s2 ignoring the case of the characters Returns The strcasecmp function returns an integer less than equal to or greater than zero if sl is found respectively to be less than to match or be greater than s2 5 14 2 8 char x strcat char x dest const char x src Concatenate two strings The strcat function appends the src string to the dest string overwriting the 0 char acter at the end of
163. rd reference or f for a forward reference These local labels may be re used within the source file references will pick the closest label with the same number and given direction Example myfunc push r push r push r18 push YL push YH eor r16 rL6 start loop ldi YL lo8 sometable idi YH hi8 sometable rjmp 2f jump to loop test at end des ld 117 Y loop continues here breq 1f return from myfunc prematurely inc r16 2 cmp r16 r18 brlo 1b jump back to top of loop pls pop YH pop YL Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 82 pop r18 pop ELJ pop rig ret Back to FAQ Index 7 3 13 How do I pass an IO port as a parameter to a function Consider this example code include lt inttypes h gt include lt avr io h gt void set_bits_func_wrong volatile uint8_t port uint8_t mask port mask void set_bits_func_correct volatile uint8_t port uint8_t mask port mask define set_bits_macro port mask port mask int main void set_bits_func_wrong PORTB Oxaa set_bits_func_correct amp PORTB 0x55 set_bits_macro PORTB Oxf0 return 0 The first function will generate object code which is not even close to what is intended The major problem arises when the function is called When the compiler sees this call it will actually pass the value in the the PORTB register using an IN instru
164. rs only if it is followed by at least one digit In no case does a non existent or small field width cause truncation of a numeric field if the result of a conversion is wider than the field width the field is expanded to contain the conversion result Since the full implementation of all the mentioned features becomes fairly large three different flavours of vfprintf can be selected using linker options The default vf printf implements all the mentioned functionality except floating point conversions A minimized version of vfprintf is available that only implements the very basic in teger and string conversion facilities but none of the additional options that can be specified using conversion flags these flags are parsed correctly from the format spec ification but then simply ignored This version can be requested using the following compiler options Wl u vfprintf 1lprintf_ min If the full functionality including the floating point conversions is required the follow ing options should be used Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 12 Standard IO facilities Wl u vfprintf 1printf_f1t lm Limitations e The specified width and precision can be at most 127 e For floating point conversions trailing digits will be lost if a number close to DBL_MAX is converted with a precision gt 0 5 12 3 32 int vfscanf FILE x _ stream const char x _fmt va list _ap Formatted in
165. rst variable is no longer used inside that function even though the variable is still in lexical scope When trying to examine the variable in avr gdb the displayed result will then look garbled So in order to avoid these side effects optimization can be turned off while debugging However some of these optimizations might also have the side effect of uncovering bugs that would otherwise not be obvious so it must be noted that turning off opti mization can easily change the bug pattern In most cases you are better off leaving optimizations enabled while debugging Back to FAQ Index 7 3 12 How do I trace an assembler file in avr gdb When using the g compiler option avr gcc only generates line number and other debug information for C and C files that pass the compiler Functions that don t have line number information will be completely skipped by a single st ep command in gdb This includes functions linked from a standard library but by default also functions defined in an assembler source file since the g compiler switch does not apply to the assembler So in order to debug an assembler input file possibly one that has to be passed through the C preprocessor it s the assembler that needs to be told to include line number information into the output file Other debug information like data types and variable allocation cannot be generated since unlike a compiler the assembler basically doesn t know about this Th
166. ry The special clobber memory informs the compiler that the assembler code may mod ify any memory location It forces the compiler to update all variables for which the contents are currently held in a register before executing the assembler code And of course everything has to be reloaded again after this code In most situations a much better solution would be to declare the pointer destination itself volatile volatile uint8_t ptr This way the compiler expects the value pointed to by ptr to be changed and will load it whenever used and store it whenever modified Situations in which you need clobbers are very rare In most cases there will be better ways Clobbered registers will force the compiler to store their values before and reload them after your assembler code Avoiding clobbers gives the compiler more freedom while optimizing your code 7 4 5 Assembler Macros In order to reuse your assembler language parts it is useful to define them as macros and put them into include files AVR Libc comes with a bunch of them which could be found in the directory avr include Using such include files may produce com piler warnings if they are used in modules which are compiled in strict ANSI mode To avoid that you can write __asm__ instead of asm and _volatile__ instead of volatile These are equivalent aliases Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 4 Inline Asm 101 Another problem with
167. s k uk A e 51 214 1 Detailed Description lt lt a serma mis 51 5 14 2 Function Documentation 52 Interrupts and Signals o o vv o X a e o 59 la Detaled Deseripnan lt s 4 4 seere edie e 4 ei 4 59 5 15 2 Denne Documentation es ssc eap pura je 62 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen CONTENTS iii ALIS Function Documentation 5 16 Special function registers i s a a sere RES a eS 5 16 1 5 16 2 Detailed Description lt s cs gas adora sku Define Documientaton lt lt 6 64 cemere edie ee ea 6 avr libc Data Structure Documentation Gl dice Sirmct Reference 2 o sa aa o Re a EWS 3 6 1 1 Detailed Description lt gt sr cse o o a a vk 4 6 4 6 2 Md SEE Referen occ odao kola ok RR 8 2 1 Detailed Deseription lt 11 racie es eee eee RS 7 avr libc Page Documentation AI Acknowledgments 0 cice don eS Bae ee Be 7 2 avr libc and assembler programs iss u k 2 121 22 t o name Invoking the compller ss se oi as Example Program lt e ooo aa 4 s Kk P amp O 4 7 3 Frequently Asked Questions 2 2 6 5 8 24s bee testes 131 dai Ta d 134 Tad LO 131 148 1359 1210 KAKA NI pea le tals FAQ ndex 12 201 22 k ee eR ar lR a 5 My program doesn t recognize a variable updated within an IMEItUptTouINE lt s e 6 k ka A a a I get undefined reference to for fun
168. sage for implementation details 5 13 4 17 void qsort void x _ base size_t _nmemb size_t _ size _ compar fn t _compar The qsort function is a modified partition exchange sort or quicksort The qsort function sorts an array of nmemb objects the initial member of which is pointed to by base The size of each object is specified by size The contents of the array base are sorted in ascending order according to a comparison function pointed to by compar which requires two arguments pointing to the objects being compared The comparison function must return an integer less than equal to or greater than zero if the first argument is considered to be respectively less than equal to or greater than the second 5 13 4 18 int rand void The rand function computes a sequence of pseudo random integers in the range of 0 to RAND_MAX as defined by the header file lt stdlib h gt The srand function sets its argument seed as the seed for a new sequence of pseudo random numbers to be returned by rand These sequences are repeatable by calling srand with the same seed value If no seed value is provided the functions are automatically seeded with a value of 1 In compliance with the C standard these functions operate on int arguments Since the underlying algorithm already uses 32 bit calculations this causes a loss of preci sion See random for an alternate set of functions that retains full 32 bit precision 5 13 4
169. sei Mane e ptr The compiler is prepared to reload this register next time it uses it Another problem with the above code is that it should not be called in code sections where interrupts are disabled and should be kept disabled because it will enable interrupts at the end We may store the current status but then we need another register Again we can solve this without clobbering a fixed but let the compiler select it This could be done with the help of a local C variable uint8_t s asm volatile in 0 _SREG_ NONE Velur n t ld _ tmp_reg__ al ANNE inc __tmp_reg__ Ane st Sal __tmp_reg__ NONE out __SREG__ 0 n t amp r s e ptr Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 4 Inline Asm 100 Now every thing seems correct but it isn t really The assembler code modifies the variable that ptr points to The compiler will not recognize this and may keep its value in any of the other registers Not only does the compiler work with the wrong value but the assembler code does too The C program may have modified the value too but the compiler didn t update the memory location for optimization reasons The worst thing you can do in this case is uint8_t s asm volatile in 0 _ SREG__ ANNE neri TANNE ld _ tmp_reg_ al TANTI inc tmp r g T PNA st Sal __tmp_reg__ Vn t out __SREG__ 530 ANNE amp r s e ptr memo
170. sing the S compiler option seems to be warranted Back to FAQ Index Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 78 7 3 8 Shouldn t I initialize all my variables Global and static variables are guaranteed to be initialized to O by the C standard avr gcc does this by placing the appropriate code into section init4 see The initN Sections With respect to the standard this sentence is somewhat simplified because the standard allows for machines where the actual bit pattern used differs from all bits being 0 but for the AVR target in general all integer type variables are set to 0 all pointers to a NULL pointer and all floating point variables to 0 0 As long as these variables are not initialized i e they don t have an equal sign and an initialization expression to the right within the definition of the variable they go into the bss section of the file This section simply records the size of the variable but otherwise doesn t consume space neither within the object file nor within flash memory Of course being a variable it will consume space in the target s SRAM In contrast global and static variables that have an initializer go into the data section of the file This will cause them to consume space in the object file in order to record the initializing value and in the flash ROM of the target device The latter is needed since the flash ROM is
171. sipi repra 16 3 7 Character Operations lt lt e ea zn st ee bea a 17 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen CONTENTS ii 5 8 39 5 14 5 7 1 Detailed Description oe ss esre cevre Dkk es 17 3 7 2 Function Documentation 2 4 2 8 2264420444 18 System Errors EMO ir eRe 20 5 8 1 Detailed Description 20 5 8 2 Define Documentation _ 2 soose eas vu kvkk Daud 20 neser Ypes ea 21 39 1 Detailed Description ee s cee eee ska eses 21 39 2 Typedef Doctmentation lt lt 2 k 8444 22 MI E 23 510 1 Detailed Description o 245i 055 8 eh e d 23 5 10 2 Define Documentation 12 1 se a g a gi 24 5 10 3 Function Documentation 4 6 65 ss suka s ees 24 Seljmp and Lonpynp i 1 cocos Be es a o 27 5 11 1 Detailed Description gt s sc co nue aos 21 5 11 2 Function Documentation 28 Standard IO facilities 1 lt o s Re EE EE e a 29 312 1 Detaled Description lt e 0 0 peseka ee 8 403 29 5 12 2 Define Documentation 2224 est e eere alk 32 3 12 3 Function Documentation o sara ee 4 33 General i o eee 42 5 13 1 Detailed Description lt 2 2 21122k kvkk a s kh 42 513 2 Define Documentation gt s h k l s O kok i Hr 44 3 133 Typedef Documentation es s sas tacne a a i 44 5 13 4 Function Documentation lt 24 4 606 5620 5400444 45 5 13 5 Variable Documentation 51 SIMI 4 b k
172. sources redhat com binutils Installation e GCC 3 3 https aee gaa org Installation AVR Libc 200208 16 cvs http savannah gnu org projects avr libc Installation Note As of 2002 08 15 the versions mentioned above are still considered experimental and must be obtained from cvs Instructions for obtaining the latest cvs versions are available at the URLs noted above Significant changes have been made which are not compatible with previous stable releases These incompatilities should be noted in the documentation 7 7 2 Optional Tools You can develop programs for AVR devices without the following tools They may or may not be of use for you e uisp 20020626 http savannah gnu org projects uisp Installation avrdude 3 1 0 http savannah nongnu org projects avrdude Installation Usage Notes GDB 5 2 1 http sources redhat com gdb Installation Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 7 Installing the GNU Tool Chain 114 e Simulavr 0 1 0 http savannah gnu org projects simulavr Installation e AVaRice 1 5 http avarice sourceforge net Installation 7 7 3 GNU Binutils for the AVR target The binutils package provides all the low level utilities needed in building and ma nipulating object files Once installed your environment will have an AVR assembler avr as linker avr 1d and librarian avr ar and avr ranlib In addi tion you get too
173. t lm A third version is available for environments that are tight on space This version is provided in the library 1ilbscanf_min a and can be requested using the following options in the link stage Wl u vfscanf lscanf_min lm In addition to the restrictions of the standard version this version implements no field width specification no conversion assignment suppression flag no n specification and no general format character matching at all All characters in fmt that do not comprise a conversion specification will simply be ignored including white space that is normally used to consume any amount of white space in the input stream However the usual skip of initial white space in the formats that support it is implemented 5 13 General utilities 5 13 1 Detailed Description include lt stdlib h gt This file declares some basic C macros and functions as defined by the ISO standard plus some AVR specific extensions Data Structures e struct div_t e struct Idiv_t Non standard i e non ISO C functions define RANDOM_MAX 0x7FFFFFFF char x itoa int __val char x__s int __radix char x Itoa long int __val char x__s int __radix char x utoa unsigned int __val char __s int __radix Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 13 General utilities 43 char ultoa unsigned long int __val char __s int __radix long random void void srandom unsigned long __seed
174. t eeaddr int len uint8_t buf uint8_t sla n 0 int rv 07 uint16_t endaddr a ORG i EE A E E E SRE E E A E E E RE a if eeaddr len lt eeaddr PAGE_SIZE 1 endaddr eeaddr len else endaddr eeaddr PAGE_SIZE 1 1 len endaddr eeaddr patch high bits of EEPROM address into SLA sla TWI_SLA_24CXX eeaddr gt gt 8 amp 0x07 lt lt 1 restart if n gt MAX_ITER return 1 begin Note 13 TWCR _BV TWINT _BV TWSTA _BV TWEN send start condition while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_REP_START OK but should not happen case TW_START break Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 11 Example using the two wire interface TWI 148 case TW_MT_ARB_LOST goto begin default return 1 error not in start condition NB do not send stop condition send SLA W TWDR sla TW_WRITE TWCR _BV TWINT _BV TWEN clear interrupt to start transmission while TWCR amp _BV TWINT 0 wait for transmission switch twst TW_STATUS case TW_MT_SLA_ACK break case TW_MT_SLA_NACK nack during select device busy writing goto restart case TW_MT_ARB_LOST re arbitrate goto begin default goto error must send stop condition TWDR eeaddr low 8 bits of addr
175. t lists printf etc are all passed on stack and char is extended to int Warning There was no such alignment before 2000 07 01 including the old patches for gcc 2 95 2 Check your old assembler subroutines and adjust them accordingly Back to FAQ Index 7 3 15 How do I put an array of strings completely in ROM There are times when you may need an array of strings which will never be modified In this case you don t want to waste ram storing the constant strings The most obvious and incorrect thing to do is this include lt avr pgmspace h gt PGM_P array 2 PROGMEM Foo Bar 1 int main void char buf 32 strcpy_P buf array 1 return 0 The result is not want you want though What you end up with is the array stored in ROM while the individual strings end up in RAM in the data section To work around this you need to do something like this Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions 86 include lt avr pgmspace h gt const char foo PROGMEM Foo const char bar PROGMEM Bar PGM_P array 2 PROGMEM foo bar 17 int main void char buf 32 strcpy_P buf array 1 return 0 Looking at the disassembly of the resulting object file we see that array is in flash as such 0000008c lt foo gt 8c 46 6f ori r20 OxF6 246 8e 6f 00 word Ox006f 2777 00000090 lt bar gt 90 42 61 ori r20 0x12
176. t set a plus sign will be used instead of a space character in this case 5 13 4 9 charx dtostrf double _val char __width char _prec char x __s The dtostrf function converts the double value passed in val into an ASCII repre sentationthat will be stored under s The caller is responsible for providing sufficient storage in s Conversion is done in the format d ddd The minimum field width of the output string including the and the possible sign for negative values is given in width and prec determines the number of digits after the decimal sign 5 13 4 10 void exit int __status Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 13 General utilities 47 The exit function terminates the application Since there is no environment to re turn to status is ignored and code execution will eventually reach an infinite loop thereby effectively halting all code processing In a C context global destructors will be called before halting execution 5 13 4 11 void free void x _ ptr The free function causes the allocated memory referenced by ptr to be made avail able for future allocations If ptr is NULL no action occurs 5 13 4 12 charx itoa int __val char x __s int _radix The function itoa converts the integer value from val into an ASCII representation that will be stored under s The caller is responsible for providing sufficient storage in s Conversion is done using
177. the C compiler Code for very time critical applications Special tweaks that cannot be done in C Usually all but the first could probably be done easily using the inline assembler facility of the compiler Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 2 avr libe and assembler programs 70 Although avr libc is primarily targeted to support programming AVR microcontrollers using the C and C language there s limited support for direct assembler usage as well The benefits of it are e Use of the C preprocessor and thus the ability to use the same symbolic constants that are available to C programs as well as a flexible macro concept that can use any valid C identifier as a macro whereas the assembler s macro concept is basically targeted to use a macro in place of an assembler instruction e Use of the runtime framework like automatically assigning interrupt vectors For devices that have RAM initializing the RAM variables can also be utilized 7 2 2 Invoking the compiler For the purpose described in this document the assembler and linker are usually not invoked manually but rather using the C compiler frontend avr gcc that in turn will call the assembler and linker as required This approach has the following advantages e There is basically only one program to be called directly avr gcc regardless of the actual source language used e The invokation of the C preprocessor will be autom
178. the only way that the compiler can tell the target device the value this variable is going to be initialized to Now if some programmer wants to make doubly sure their variables really get a 0 at program startup and adds an initializer just containing 0 on the right hand side they waste space While this waste of space applies to virtually any platform C is implemented on it s usually not noticeable on larger machines like PCs while the waste of flash ROM storage can be very painful on a small microcontroller like the AVR So in general variables should only be explicitly initialized if the initial value is non Zero Back to FAQ Index 7 3 9 Why do some 16 bit timer registers sometimes get trashed Some of the timer related 16 bit IO registers use a temporary register called TEMP in the Atmel datasheet to guarantee an atomic access to the register despite the fact that two separate 8 bit IO transfers are required to actually move the data Typically this includes access to the current timer counter value register TCNTn the input capture register ICRn and write access to the output compare registers OCRnM Refer to the actual datasheet for each device s set of registers that involves the TEMP register When accessing one of the registers that use TEMP from the main application and possibly any other one from within an interrupt routine care must be taken that no access from within an interrupt context could clobber t
179. the standard library libc a will always be searched for unresolved references when the linker is started using the C compiler frontend i e there s always at least one implied 1c option the mathematics library 1ibm a needs to be explicitly requested using 1m See also the entry in the FAQ explaining this Conventionally Makefiles use the make macro LDLIBS to keep track of 1 and possibly L options that should only be appended to the C compiler command line when linking the final binary In contrast the macro LDF LAGS is used to store other command line options to the C compiler that should be passed as options during the linking stage The difference is that options are placed early on the command line while libraries are put at the end since they are to be used to resolve global symbols that are still unresolved at this point Specific linker flags can be passed from the C compiler command line using the W1 compiler option see above This option requires that there be no spaces in the appended linker option while some of the linker options above like Map or defsym would require a space In these situations the space can be replaced by an equal sign Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 10 A simple project 128 as well For example the following command line can be used to compile foo c into an executable and also produce a link map that contains a cross reference list in the file f
180. then A0 refers to r 30 and BO refers to r31 But both versions will fail during the assembly stage of the compiler if you explicitely need Z like in ld r24 Z If you write ld r24 a0 with a lower case a following the percent sign then the compiler will create the proper assembler line 7 4 4 Clobbers As stated previously the last part of the asm statement the list of clobbers may be omitted including the colon seperator However if you are using registers which had not been passed as operands you need to inform the compiler about this The following example will do an atomic increment It increments an 8 bit value pointed to by a pointer variable in one go without being interrupted by an interrupt routine or another thread in a multithreaded environment Note that we must use a pointer because the incremented value needs to be stored before interrupts are enabled Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 4 Inline Asm asm volatile olim n t ld r24 a0 n t minesr24 miki st a0 r24 mat sei n t e ptr r24 The compiler might produce the following code ELI ld r24 Z inc r24 st Z r24 sei One easy solution to avoid clobbering register r24 is to make use of the special tem porary register __tmp_reg__ defined by the compiler asm volatile tela A ld _ tmp_reg__ a0 MAMA Y inc __tmp_reg__ In E st a0 __tmp_reg__ Mn VET
181. there must be enough room for all the characters no terminating NUL is added The usual skip of leading white space is suppressed To skip white space first use an explicit space in the format Matches a nonempty sequence of characters from the specified set of accepted characters the next pointer must be a pointer to char and there must be enough room for all the characters in the string plus a terminating NUL character The usual skip of leading white space is suppressed The string is to be made up of characters in or not in a particular set the set is defined by the characters between the open bracket character and a close bracket character The set excludes those characters if the first character after the open bracket is a circum flex To include a close bracket in the set make it the first character after the open bracket or the circumflex any other position will end the set The hyphen character is also special when placed between two other characters it adds all intervening characters to the set To include a hyphen make it the last character before the final close bracket For instance 0 9 means the set of every thing except close bracket zero through nine and hyphen The string ends with the appearance of a character not in the or with a circumflex in set or when the field width runs out p Matches a pointer value as printed by p in printf the next pointer must be a pointer to void n Nothing is e
182. these names in definitions for numerical constants a way is needed to convert a bit number usually within a byte register into a byte value that can be assigned directly to the register However sometimes the direct bit numbers are needed as well e g in an sbi call so the definitions cannot usefully be made as byte values in the first place So in order to access a particular bit number as a byte value use the BV macro Of course the implementation of this macro is just the usual bit shift which is done by the compiler anyway thus doesn t impose any run time penalty so the following applies _BV 3 gt 1 lt lt 3 gt 0x08 However using the macro often makes the program better readable BV stands for bit value in case someone might ask you Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 3 Frequently Asked Questions Example clock timer 2 with full IO clock CS2x 0b001 toggle OC2 output on compare match COM2x 0b01 and clear timer on compare match CTC2 1 Make OC2 PD7 an output TCCR2 _BV COM20 _BV CTC2 _BV CS20 DDRD _BV PD7 Back to FAQ Index 7 3 7 Can I use C on the AVR Basically yes C is supported assuming your compiler has been configured and compiled to support it of course Source files ending in cc cpp or C will automat ically cause the compiler frontend to invoke the C compiler Alternatively the C compiler could
183. tical and the operation can be interrupted the programmer is the responsible for disabling interrupts before accessing the register pair Note The order of the arguments was switched in older versions of avr libc versions lt 20020203 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 6 avr libc Data Structure Documentation 68 5 16 2 14 define sbi sfr bit SFR BYTE sfr BV bit include lt avr io h gt Set bit bit in IO register sfr 6 avr libc Data Structure Documentation 6 1 div_t Struct Reference 6 1 1 Detailed Description Result type for function div The documentation for this struct was generated from the following file e stdlib h 6 2 1div_t Struct Reference 6 2 1 Detailed Description Result type for function 1div The documentation for this struct was generated from the following file e stdlib h 7 avr libc Page Documentation 7 1 Acknowledgments This document tries to tie together the labors of a large group of people Without these individuals efforts we wouldn t have a terrific free set of tools to develop AVR projects We all owe thanks to e The GCC Team which produced a very capable set of development tools for an amazing number of platforms and processors e Denis Chertykov denisc overta ru for making the AVR specific changes to the GNU tools Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 2 avr libc and assembler pro
184. ting point number 5 10 3 11 double fmod double __x double __y The function fmod returns the floating point remainder of x y 5 10 3 12 double frexp double __value int x __exp The frexp function breaks a floating point number into a normalized fraction and an integral power of 2 It stores the integer in the int object pointed to by exp The frexp function returns the value x such that x is a double with magnitude in the interval 1 2 1 or zero and value equals x times 2 raised to the power exp If value is zero both parts of the result are zero 5 10 3 13 double inverse double The function inverse returns 1 x Note This function does not belong to the C standard definition 5 10 3 14 int isinf double _x The function isinf returns 1 if the argument x is either positive or negative infinity otherwise 0 5 10 3 15 int isnan double __x The function isnan returns 1 if the argument x represents a not a number NaN object otherwise 0 Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 10 Mathematics 26 5 10 3 16 double Idexp double _x int __exp The ldexp function multiplies a floating point number by an integral power of 2 The Idexp function returns the value of x times 2 raised to the power exp If the resultant value would cause an overflow the global variable errno is set to ERANGE and the value NaN is returned 5 10 3 17 double log double __x
185. to a matching member of the array or a null pointer if no match is found If two members compare as equal which member is matched is unspecified 5 13 4 6 void calloc size_t __nele size_t __size Allocate nele elements of size each Identical to calling malloc using nele size as argument except the allocated memory will be cleared to zero 5 13 4 7 div t div int num int _denom The div function computes the value num denom and returns the quotient and re mainder in a structure named div_t that contains two int members named quot and rem 5 13 4 8 charx dtostre double __val char x __s unsigned char _ prec unsigned char _ flags The dtostre function converts the double value passed in val into an ASCII repre sentation that will be stored under s The caller is responsible for providing sufficient storage in s Conversion is done in the format d ddde177dd where there is one digit be fore the decimal point character and the number of digits after 1t is equal to the preci sion prec if the precision is zero no decimal point character appears If flags has the DTOSTRE UPPERCASE bit set the letter E rather than e will be used to introduce the exponent The exponent always contains two digits if the value is zero the exponent is 00 If flags has the DTOSTRE_ALWAYS_SIGN bit set a space character will be placed into the leading position for positive numbers If flags has the DTOSTRE_PLUS_SIGN bi
186. ts to detect the bottom of stack in or der to prevent a stack heap collision when extending the actual size of the heap to gain more space for dynamic memory It will not try to go beyond the current stack limit decreased by _malloc_margin bytes Thus all possible stack frames of interrupt routines that could interrupt the current function plus all further nested function calls must not require more stack space or they will risk colliding with the data segment The default value of _malloc_margin is set to 32 7 5 4 Implementation details Dynamic memory allocation requests will be returned with a two byte header prepended that records the size of the allocation This is later used by free The returned address points just beyond that header Thus if the application accidentally writes before the returned memory region the internal consistency of the memory al locator is compromised The implementation maintains a simple freelist that accounts for memory blocks that have been returned in previous calls to free Note that all of this memory is considered to be successfully added to the heap already so no further checks against stack heap collisions are done when recycling memory from the freelist The freelist itself is not maintained as a separate data structure but rather by modifying the contents of the freed memory to contain pointers chaining the pieces together That way no additional memory is reqired to maintain this list exce
187. u must subtract 0x20 from them For more backwards compatibility insert the following at the start of your old assem bler source file define __SFR_OFFSET 0 This automatically subtracts 0x20 from I O space addresses but it s a hack so it is recommended to change your source wrap such addresses in macros defined here as shown below After this is done the _SFR_OFFSET definition is no longer necessary and can be removed Real example this code could be used in a boot loader that is portable between devices with SPMCR at different addresses lt avr iom163 h gt define SPMCR _SFR_IO8 0x37 lt avr iom128 h gt define SPMCR _SFR_MEM8 0x68 if _SFR_IO_REG_P SPMCR out _SFR_IO_ADDR SPMCR r24 else sts _SFR_MEM_ADDR SPMCR r24 endif You can use the in out cbi sbi sbic sbis instructions without the _SFR_ IO_REG_P test if you know that the register is in the I O space as with SREG for example If it isn t the assembler will complain I O address out of range 0 0x3f so this should be fairly safe If you do not define __SFR_OFF SET so it will be 0x20 by default all special register addresses are defined as memory addresses so SREG is 0x5f and if code size and speed are not important and you don t like the ugly if above you can always use Ids sts to access them But this will not work if _SFR_OFFSET 0x20 so use a different macro defined only if __SFR_OFF SET 0x20 fo
188. uction of course provided the target address is within the allowable range for this instruction and the right hand side of the expression is a constant value known at compile time The advantage of using the memory mapped paradigm in C programs is that it makes the programs more portable to other C compilers for the AVR platform Some people might also feel that this is more readable For example the following two statements would be equivalent outb DDRD inb DDRD amp LCDBITS DDRD amp LCDBITS The generated code is identical for both Whitout optimization the compiler strictly generates code following the memory mapped paradigm while with optimization turned on code is generated using the faster and smaller in out MCU instructions Note that special care must be taken when accessing some of the 16 bit timer IO reg isters where access from both the main program and within an interrupt context can happen See Why do some 16 bit timer registers sometimes get trashed Modules e Additional notes from lt avr sfr_defs h gt Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 16 Special function registers 65 Bit manipulation e define BV bit 1 lt lt bit IO operations define inb sfr SFR_BYTE sfr define inw sfr SFR WORD sfr define outb sfr val SFR_BYTE sfr val define outw sfr val SFR WORD sfr val IO register bit manipulation define cbi sfr bit
189. uence of digits optionally containing a decimal point character optionally fol lowed by an exponent An exponent consists of an E or e followed by an optional plus or minus sign followed by a sequence of digits Leading white space characters in the string are skipped The strtod function returns the converted value if any If endptr is not NULL a pointer to the character after the last character used in the conversion is stored in the location referenced by endpt r If no conversion is performed zero is returned and the value of npt r is stored in the location referenced by endpt r If the correct value would cause overflow plus or minus HUGE_VAL is returned ac cording to the sign of the value and ERANGE is stored in errno If the correct value would cause underflow zero is returned and ERANGE is stored in errno FIXME HUGE_VAL needs to be defined somewhere The bit pattern is Ox7fffffff but what number would this be 5 13 4 25 long strtol const char _nptr char x __endptr int __base Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 13 General utilities 50 The strtol function converts the string in nptr to a long value The conversion is done according to the given base which must be between 2 and 36 inclusive or be the special value 0 The string may begin with an arbitrary amount of white space as determined by iss pace followed by a single o
190. urn anyway However this also turns off all optimizations normally done by the compiler which assume that functions known by a certain name be have as described by the standard E g applying the function strlen to a literal string will normally cause the compiler to immediately replace that call by the actual length of the string while with f freestanding it will always call strlen at run time e funsigned char Make any unqualfied char type an unsigned char Without this option they default to a signed char e funsigned bitfields Make any unqualified bitfield type unsigned By default they are signed e fshort enums Allocate to an enum type only as many bytes as 1t needs for the declared range of possible values Specifically the enum type will be equivalent to the smallest integer type which has enough room Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 9 Using the GNU tools 125 e fpack struct Pack all structure members together without holes 7 9 2 Options for the assembler avr as 7 9 2 1 Machine specific assembler options e mmcu architecture e mmcu MCU name avr as understands the same mmcu options as avr gcc By default avr2 is as sumed but this can be altered by using the appropriate ar ch pseudo instruction inside the assembler source file e mall opcodes Turns off opcode checking for the actual MCU type and allows any possible AVR opcode to be asse
191. variable will take place Refer to How to modify MCUCR or WDTCR early for a description how to do this using few lines of assembler code or to the chapter about memory sections for an example written in C The explanation of malloc contains a discussion about the use of internal RAM vs external RAM in particular with respect to the various possible locations of the heap area reserved for malloc It also explains the linker command line options that are required to move the memory regions away from their respective standard locations in internal RAM Finally if the application simply wants to use the additional RAM for private data storage kept outside the domain of the C compiler e g through a char variable initialized directly to a particular address it would be sufficient to defer the initializa tion of the external RAM interface to the beginning of main so no tweaking of the init1 section is necessary The same applies if only the heap is going to be located there since the application start up code does not affect the heap It is not recommended to locate the stack in external RAM In general accessing exter nal RAM is slower than internal RAM and errata of some AVR devices even prevent this configuration from working properly at all Back to FAQ Index 7 3 17 Which O flag to use There s a common misconception that larger numbers behind the O option might auto matically cause better optimization First th
192. vr directory does not exist you should create it before trying to install anything You will need root access to install there If you don t have root access to the system you can alternatively install in your home directory for exam ple in SHOME local avr Where you install is a completely arbitrary decision but should be consistent for all the tools You specify the installation directory by using the prefix dir option with the configure script It is important to install all the AVR tools in the same directory or some of the tools will not work correctly To ensure consistency and simplify the discussion we will use PREF IX to refer to whatever directory you wish to install in You can set this as an environment variable if you wish as such using a Bourne like shell PREFIX HOME local avr export PREFIX Note Be sure that you have your PATH environment variable set to search the direc tory you install everything in before you start installing anything For example if you use prefix PREFIX you must have SPREFIX bin in your exported PATH As such PATH SPATH SPREFIX bin export PATH Note The versions for the packages listed below are known to work together If you mix and match different versions you may have problems Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 7 Installing the GNU Tool Chain 113 7 71 Required Tools e GNU Binutils 2 14 http
193. witch direction Note 3 case UP if pwm 1023 direction DOWN break case DOWN if pwm 0 direction UP break OCR pwm Note 4 void ioinit void Note 5 tmrl is 10 bit PWM TCCR1A _BV PWM10 _BV PWM11 _BV XCOM11 tmrl running on full MCU clock TCCRIB _BV CS10 set PWM value to 0 OCR 0 enable OC1 and PB2 as output DDROC _BV OC1 timer_enable_int _BV TOIE1 enable interrupts sei int main void Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 7 10 A simple project 132 ioinit loop forever the interrupts are doing the rest for Note 6 return 0 7 10 3 Compiling and Linking This first thing that needs to be done is compile the source When compiling the compiler needs to know the processor type so the mmcu option is specified The Os option will tell the compiler to optimize the code for efficient space usage at the possible expense of code execution speed The g is used to embed debug info The debug info is useful for disassemblies and doesn t end up in the hex files so I usually specify it Finally the c tells the compiler to compile and stop don t link This demo is small enough that we could compile and link in one step However real world projects will have several modules and will typically need to break up the building
194. xpected instead the number of characters consumed thus far from the input is stored through the next pointer which must be a pointer to int This is not a conversion although it can be suppressed with the x flag These functions return the number of input items assigned which can be fewer than provided for or even zero in the event of a matching failure Zero indicates that while there was input available no conversions were assigned typically this is due to an invalid input character such as an alphabetic character for a d conversion The value EOF is returned if an input failure occurs before any conversion such as an end of file occurs If an error or end of file occurs after conversion has begun the number of conversions which were successfully completed is returned Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen 5 13 General utilities 42 By default all the conversions described above are available except the floating point conversions and the conversion These conversions will be available in the ex tended version provided by the library 1ibscanf_flt a Note that either of these conversions requires the availability of a buffer that needs to be obtained at run time using malloc If this buffer cannot be obtained the operation is aborted returning the value EOF To link a program against the extended version use the following compiler flags in the link stage W1 u vfscanf lscanf_fl
195. xygen INDEX 159 ispunct memcpy _P ctype 18 avr_pgmspace 9 isspace memmove ctype 18 avr_string 52 isupper memset ctype 18 avr_string 53 isxdigit modf ctype 18 avr_math 25 itoa avr_stdlib 46 outb avr_sfr 66 labs outp avr_stdlib 46 avr_sfr 66 Idexp outw avr_math 24 avr_sfr 66 Idiv avr_stdlib 46 PGM_P Idiv_t 67 avr_pgmspace 8 log PGM_VOID P avr_math 25 avr_pgmspace 8 log10 pow avr_math 25 avr_math 25 longjmp Power Management and Sleep Modes setjmp 27 13 loop_until_bit_is_clear PRG_RDB avr_sfr 65 avr_pgmspace 8 loop_until_bit_is_set printf avr_sfr 66 avr_stdio 35 Itoa printf_P avr_stdlib 46 avr_stdio 35 Program Space String Utilities 7 M_PI PSTR avr_math 23 avr_pgmspace 9 M_SQRT2 putc avr_math 23 avr_stdio 31 malloc putchar avr_stdlib 46 avr_stdio 31 Mathematics 22 puts memccpy avr_stdio 35 avr_string 51 puts_P memchr avr_stdio 35 avr_string 51 memcmp qsort avr_string 52 avr_stdlib 47 memcpy avr_string 52 rand Generated on Tue Apr 22 09 54 12 2003 for avr libc by Doxygen INDEX 160 avr_stdlib 47 RAND_MAX avr_stdlib 43 rand_r avr_stdlib 47 random avr_stdlib 47 RANDOM_MAX avr_stdlib 43 random r avr_stdlib 48 sbi avr_sfr 66 scanf avr_stdio 35 scanf_P avr_stdio 35 sel avr interrupts 61 set_sleep_mode avr_sleep 14 setjmp longjmp 27 setimp 27 Setjmp and Longjmp 26 SIGNAL avr_interrupts 61 sin avr_
196. y Doxygen 7 10 A simple project 0x00800060 PROVIDE __data_start data gnu linkonce d 0x00800060 ALIGN 0x2 0x00800060 _edata 0x00800060 PROVIDE __data_end bss 0x00800060 0x3 0x00800060 PROVIDE __bss_start Abs COMMON COMMON 0x00800060 0x3 demo o 0x0 size before relaxing 0x00800060 direction 0x00800061 pwm 0x00800063 PROVIDE __bss_end 0x000000ca __data_load_start LOADADDR 0x000000ca __data_load_end __data_load_start SIZEOF noinit 0x00800063 0x0 0x00800063 PROVIDE __noinit_start enoinit 0x00800063 PROVIDE __noinit_end 0x00800063 _end 0x00800063 PROVIDE __heap_start eeprom 0x00810000 0x0 load address 0x000000ca eeprom 0x00810000 _ eeprom_end The last address in the t ext segment is location 0x 2 denoted by etext so the instructions use up 242 bytes of FLASH The data segment where initialized static variables are stored starts at location 0x60 which is the first address after the register bank on a 2313 processor The next available address in the data segment is also location 0x 60 so the appli cation has no initialized data The bss segment where uninitialized data is stored starts at location 0x 60 The next available address in the oss segment is location 0x63 so the application uses 3 bytes of uninitialized data The eeprom segment where EEPROM variables are stored starts at location 0x0 The next av
197. ze of the array the array must contain a terminating NUL character e AS is written No argument is converted The complete conversion specifica tion is e cE The double argument is rounded and converted in the format d ddde177dd where there is one digit before the decimal point char acter and the number of digits after it is equal to the precision if the precision is missing it is taken as 6 if the precision is zero no decimal point character appears An E conversion uses the letter E rather than e to introduce the exponent The exponent always contains two digits if the value is zero the exponent is 00 e fF The double argument is rounded and converted to decimal notation in the format ddd ddd where the number of digits after the decimal point character is equal to the precision specification If the precision is missing it is taken as 6 if the precision is explicitly zero no decimal point character appears If a decimal point appears at least one digit appears before it e gG The double argument is converted in style or e or F or E for G conver sions The precision specifies the number of significant digits If the precision is missing 6 digits are given if the precision is zero it is treated as 1 Style e is used if the exponent from its conversion is less than 4 or greater than or equal to the precision Trailing zeros are removed from the fractional part of the result a decimal point appea

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