Programming the AVR microcontroller with GCC
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1. 1 x 220 Ohm resistor color code red red brown 2 x 470 Ohm resistor color code yellow purple brown In addition to the above parts you need a 5V electronically stabilized DC power supply or you can use a 4 5V battery as power supply You have probably noticed that we do not need a crystal This is because the ATmega8 has now a build in oscilator This oscilator can be used when accurate timing is not an issue However if you want to build precise measurement equipment or you want to use the UART RS232 interface then you will need a crystal Which type of oscilator is used can be defined via fuse bits which you can modify with the programmer By default factory setting the internal 1Mhz oscilator is active Building the programmer hardware The AVR microcontrollers allows for in circuit programming ISP That is you do not need to remove the microcontroller form the board a EN to program it You will see that you can get different programmer hardware from 50 150 Euro However with Linux running it is also possible to build a very simple programmer that does the job You need a free parallel port on your computer and the following cable Note that this is an improved programmer compared to the one presented in the March 2002 article We build the protection resistors into the programmer This will then save some space and parts on the circuit board The wiring for the programmer cable has to be as follows pin on pcb pin on2. AVR protection resistor Pin on parallel port S Re pooo mooo a MOn aom O B MISO 8 200mm Biyah 2 SCK 19 4700hm Strobe I Se aa Se a The cable should not be longer than 70cm The protection resistors can be build into the connector as show on the picture on the right Writing software The Atmeag 8 can be programmed in plain C with the help of gcc To know some AVR assembler can be useful but it is not needed The AVR libc comes with an avr libc user manual 1 0 4 pdf 1139921 bytes which documents all functions available in C From Atmel s website www atmel com go to avr products gt 8 bit risc gt Datasheets you can download the complete data sheet It describes all the registers and how to use the CPU One thing to keep in mind when using a microcontroller is that it has only a few bytes of Ram That means you must not declare large data structures or strings Your program should not use deeply nested function calls or recursion Much better than all theory is a real example We will write a program that causes our LED to blink in 0 5 seconds intervals Not very useful but very good to get started The avr libc has changed a lot Previously you did set a bit on a port with sbi and you cleared it with cbi Now those functions are deprecated First I present the good old way 5 of 8 352 Programming the AVR microcontroller with GCC libe 1 0 4 i defines or Luture Compatibility 7 aL IEMeSie coi tde
3. later series of articles we will again build interesting hardware but this time based on the ATmega8 Introduction Many people where interested in microcontroller programming after the article which I wrote in 2002 However this first step to get the development environment up and running is the hardest If something does not work then you have absolutely no clue where the fault is Programmer cable wrong Circuit faulty Installation incorrect Parallelport disabled in bios Kernel modules for ppdev compiled wrong There can be a lot of reasons why things don t work To make the entrance to the exciting world of microcontrollers easier shop tuxgraphics org offers now a bootable CD with a manual and the programmer hardware All you need to do then is boot from this CD and everything is up and running No software installation is lof8 352 Programming the AVR microcontroller with GCC libe 1 0 4 required and nothing is modified on your local computer Even I use such a CD now for a while because the hardware I build often survives several generations of kernels and software installations on my PC If I want later on to update some microcontroller software then I do not have to worry if the development environment on my Linux PC is still working I just boot from the CD and it is up and running Independent of this CD I will explain the installation of the GCC avr development environment in the following paragraphs If you have the CD fro
4. 352 Programming the AVR microcontroller with GCC libe 1 0 4 Home Electronics Graphics Film amp Animation E cards Other Linux stuff Photos Online Shop fe Katja Socks Content A Programming the AVR microcontroller with GCC Software installation libc 1 0 4 What you need e Software installation GNU binutils e Software installation AVR gcc e Software installation The AVR C library e Software installation The Programmer A small test project Linux amp GCC e Needed Hardware e Building the programmer hardware ALAE 2 iu SoS a The AVR 8 Bit RISC microcontroller from Atmel is a very common e Compiling and loading 4 ee es riage Some micreetii microcontroller This microcontroller is one chip with EEPROM Ram Analog to ie Digital converter a lot of digital input and output lines timers UART for RS 232 Teac and Guseestons communication and many other things ideas and suggestions Se Roletne The best is however that a complete programming environment is available under Linux You can program this microcontroller in C using GCC I wrote already in March 2002 an article about the same subject A lot of things have changed in the avr libc development and the AT90S4433 microcontroller which I used in 2002 is no longer manufactured by Atmel This is therefore an update of the March 2002 article I will use libc 1 0 4 and the ATmega8 microcontroller This article shall be only an introduction and in a
5. This would be a waste of CPU time and slow the system very much down In the case of the AVR this is different We don t have several tasks and there is no other program running There is not even an operating system It is therefore quite normal to busy loop forever Compiling and loading Before you start make sure that you have usr local avr bin in the PATH If needed edit your bash_profile or tcshrc and add 6 of 8 352 Programming the AVR microcontroller with GCC libe 1 0 4 We use the parallel port and uisp to program the AVR Uisp uses the ppdev interface of the kernel Therefore you need to have the following kernel modules loaded Check with the command sbin Ismod that they are loaded otherwise load them as root with It is a good idea to execute these commands automatically during startup You can add them to a rc script e g for Redhat etc re d re local To use the ppdev interface as normal user root needs to give you write access by once running the command Make as well sure that no printer daemon is running on the parallel port If you have one running then stop it before you connect the programmer cable Now everything is ready to compile and program our microcontroller The package for our test program avrm8ledtest 0 1 tar gz includes a make file All you need to do is type make make load This will compile and load the software I will not go into the details of all the commands You can see them i
6. e AVR microcontroller with GCC libe 1 0 4 Software installation AVR gcc avr gcc will be our C compiler Run the following command to build and install it car TROVE CiOCHCORS 3 452 scare O22 col Gee 3 54 2 mkdir obj avr cd obj avr gt o COME LEME target avr prefix usr local avr disable nls nable languac make i S COGEs make install Software installation The AVR C library The C library is quite stable now compared to the one I presented in March 2002 Run the following command to build and install it kar ero ae 0 4 tae lo2Z cel avie lile 1 0 4 PREFIX usr local avr export PREEIX Sm x o COCOME domake eel lows Jlel HAS Coors make install Software installation The Programmer The programmer software loads the specially prepared object code into the EEPROM of our microcontroller The uisp programmer for Linux is a very good programmer It can be used directly from within a Makefile You just add a make load rule and you can compile and load the software in one go uisp is installed as follows Carnin Ee WL Sjo ZOOULOSII tae a tae ca uisp 20040311 configure prefix usr local avr make as root make install A small test project 3 of 8 352 Programming the AVR microcontroller with GCC libe 1 0 4 We will start with a small test circuit which you can expand later on This circuit can also be used as a simple test environment for more complex hard
7. fine Ccoi str bit SER BYTE Str amp BV bit endif ifndef sbi defrine Soi str bit ES EREB TESTE BV bate endif void main void 7 INTTIALIZE enable PC5 as output sbi DDRC PC5 BLINK BLINK while 1 led on pin 0 COINPRPORTC ECS delay_ms 500 eer outout tO SW DAD OFE Slow PORIC PCS p delay_ms 500 The following example does exactly the same but uses the new syntax void main void 7 INITIALIZE enable PC5 as output DDRC _BV PC5 BLINK BLINK ooo PC5 is 5 see file include avr iom8 h and _BV PC5 is 00100000 M while 1 led on pin 0 PORICE _BW PCS p delay_ms 500 Je eer Owlcjowic cO SW MD Ore PORTE BW PCS p delay_ms 500 The above code snipet shows how simple it is to write a program You see only the main program the delay_ms function is included in the full listing avrm8ledtest c To use pin PCS as output you need to set the PCS bit in the data direction register for port C DDRC After that you can set PCS to OV with the function cbi PORTC PCS clear bit PC5 or to 5V with sbi PORTC PCS set bit PC5 The value of PC5 is defined in iom8 h which is included via io h You don t have to worry about it If you have already written programs for multi user multi tasking systems such as Linux you know that one must never program a non blocking endless loop
8. m tuxgraphics then continue with chapter A small test project Software installation What you need To use the GNU C development environment you need the following software Available from ftp ftp gnu org gnu binutils or any mirror E g ftp gatekeeper dec com pub GNU binutils Available from ftp ftp gnu org gnu gcc gcec core 3 4 2 tar bz2 or any mirror E g ftp gatekeeper dec com pub GNU gcc avr libc 1 0 4 tar bz2 The AVR C library is available from http savannah nongnu org projects avr libc uisp 20040311 tar bz2 The AVR programmer software is available from http savannah nongnu org projects uisp binutils 2 15 tar bz2 We will install all the programs to usr local avr This is to keep the program separate from your normal Linux C compiler Create this directory with the command Software installation GNU binutils The binutils package provides all the low level utilities needed for building object files It includes an AVR assembler avr as linker avr ld library handling tools avr ranlib avr ar programs to generate object files loadable to the microcontroller s EEPROM avr objcopy disassembler avr objdump and utilities such as avr strip and avr size Run the following commands to build and install the binutils Add the line usr local avr lib to the file etc ld so conf and run the command sbin Idconfig to rebuild the linker cache 2 of 8 352 Programming th
9. n the Makefile and they are always the same I can my self not remember all of them I just know that I need to use make load If you want to write a different program then just replace all occurrences of avrm8ledtest in the Makefile with the name of your program Some interesting binutils More interesting than the actual compilation process are some of the binutils Those utilities have however not really changed since March 2002 Take a look at the Some interesting binutils chapter in article231 March 2002 Ideas and suggestions The ATmega8 is compatible to the AT90S4433 for most uses You need to program the fuse bits to use the external oscilator and the previously presented hardware might work with possibly minor changes Unfortunatley I have not had time yet to re test all circuits for the ATmega8 If you want to be on the save side then use the AT90S4433 for the old articles If you don t mind to troubleshoot and solve problems then try the ATmega8 with the old articles circuits Here is a list of those previous hardware articles A LCD control panel for your Linux server A microcontroller based DC power supply Frequency counter 1Hz 100Mhz with LCD display and RS232 interface Linux USB LCD display with watchdog and buttons Building an autonomous light finder robot Note the programmer presented here includes already the protection resistors which were build into the circuit board Tof8 352 Programming the AVR microco
10. ntroller with GCC libe 1 0 4 in the older hardware articles To use the new programmer with the old boards you will just need to replace the protection resistors on the board by wires Atmel provides an application note AVR081 Replacing AT90S4433 by ATmega8 which lists all the incompatibilities at90s4433_to_atmega8 pdf 101343 bytes References e Pascal Stang s AVRHb http www procyonengineering com avr avrlib index html or http hubbard engr scu edu embedded avr avrlib the tavrasm assembler for Linux www tavrasm org All software and documents mentioned in this article The atmel website www atmel com Electronic pages from the tuxgraphics shop shop tuxgraphics org Here you can get the Linux AVR programming CD kits and microcontrollers lt tuxgraphics Home Go to the index of this section Guido Socher tuxgraphics org 2005 02 26 generated by tuxgrparser version 2 52 8 of 8
11. ware You can easily test load software and attach sensors or measurement equipment Our test program as presented here will just cause a LED to blink ATmega8 amp test circuit RXD PDO d2 to PC Programmer Cable with internal protection resistors ATmega8 amp Needed Hardware You need the parts listed in the table below Although it is a very common microcontroller it might not be available in every local radio shop but bigger distributors for electronic components like www conrad de germany www selectronic fr france digikey com US CA etc have it in store The best place to get the microcontroller and the other parts is however shop tuxgraphics org 1 x ATmega8 DIP version Atmel 8 bit Avr risc processor 1 x 28 pin 7 5mm IC socket The 28 pin socket is a bit more difficult to get Usually the 28 sockets are 14mm wide but we need a 7 5mm socket x resistor color code brown black orange 1 x IK resistor color code brown black red 1 x 10uF electrolytic capacitor Some wires 1x LED 4 of 8 352 Programming the AVR microcontroller with GCC libe 1 0 4 matrix board The following is needed for the programmer not needed if you get the Linux AVR programming kit from tuxgraphics 1 x DB25 connector to plug into the parallel port Any kind of 5 pin connector socket for the programmer I recommend to use precision strip connectors similar to IC sockets and break 5 pins off
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