Low Power and Embedded Systems
Contents
1. Low Power and Embedded Systems Workbook 1 Table of Contents IAEFOGU CUO sect EIEEE A EE PAE ott Sea ere ieee oa eee Baton EANA an A A EE 1 DOCUMENT CONVENTIONS nia a a a a Maades lv adh ebbv ered aa a Aaa a A I eead eveeushes 2 Supporting maternal penetasan eanan nuena rohama ENE aA AAAA aa peeks ela ee tase eee 2 Workbooks structure sse A A N a a a TA A 3 WhatISINGCC 0 MADENE E AE EEE A EA AN 3 EXEICISES lt 2 naa N N N a ei bal saan ena NEA 5 EIE a EE E AEO E E AESI EE EI AORE AA A A A E AEAEE 5 Exercise 2 Flash an LED ritinn a N A a e a A EA 8 ES E AACE A A deste ae EE E ae ees gaan Ou dean E T EEA bane 11 PNA a aa a a a a A a ee E Ae a 11 Introduction The aim of this module is to teach students how to design and write programs for low power embedded devices that communicate with other computers or devices to solve practical problems The course will cover the relevant theoretical knowledge required for writing such applications and provide practical experience writing C programs for the Atmel family of microcontrollers The module will also give students an appreciation for some of the issues when designing low power embedded systems For each of the first 4 weeks of this 8 week course you will be provided with a workbook like this one It contains step by step instructions for you to follow and links to reference material Each workbook contains a number of exercises Completion of these exercises must be verified by a d2. differ in their power Low Power and Embedded Systems Workbook 1 consumption The devices you will use may be marked ATMEGA644P or ATMEGAG644PA Makefile http Awww cl cam ac uk teaching 1314 P31 code workbook1_Makefile A Makefile template used in Exercise 1 avr libc documentation http Awww nongnu org avr libc Documentation for libraries available on the PCs for the Atmel range of microcontrollers breadboard_program pdf http Awww cl cam ac uk teaching 1314 P31 docs breadboard_program pdf A circuit diagram for connecting a programming header to the microcontroller Programming header http Awww cl cam ac uk teaching 1314 P31 docs programming_header jpg Photograph showing the connections for in circuit programming of the microcontroller AVR GCC tutorial http winavr scienceprog com avr gcc tutorial Tutorial for AVR GCC Workbooks structure Workbook 1 will cover Microcontroller Clock sources and very basic I O Workbook 2 will cover basic Serial communication Serial communication using interrupts and the use of the Analogue to Digital converter Workbook 3 will cover the use of timers in the microcontroller and adding an LCD display for more readable output Workbook 4 will cover interrupts generated from transitions on inputs and use these to create a precision interval display It will also cover the sleep modes for the microcontroller What is Needed Hardware e A microcontroller Integrat
3. exercise 2 will use the rest of the Makefile Low Power and Embedded Systems Workbook 1 CPPFLAGS I I lib MCU atmega644p VPATH lib all exercisel hex xercisel elf exercisel o o o 0 3 c avr gec CPPFLAGS Os mmcu MCU o c elf 3 0 avr gcc Os mmcu MCU o o hex elf avr objcopy j text j data O ihex S lst elf avr objdump h S gt Q clean rm f o elf hex lst program exercisel hex avrdude p m644 P dev ttyUSBO c avrusb500 e U flash w fuses avrdude p m644 P dev ttyUSBO c avrusb500 e U hfuse w 0x99 m avrdude p m644 P dev ttyUSBO c avrusb500 e U lfuse w 0x62 m The Makefile you have just created contains the default settings for the hfuse 0x99 and Ifuse 0x62 Edit the hfuse and Ifuse values to those you worked out previously and checked earlier with a demonstrator In these workbooks we don t need to change the extended fuse setting You might also need to edit the references to dev ttyUSBO to match the those of actual device See the previous section The Programmer Here is a brief explanation of the line you have just edited note this is only for information avrdude The linux program used to program the device p m644 Tells avrdude the device type being programmed the device signature is checked before programming P dev ttyUSBO Tells avrdude where the programmer is attached c avrusb
4. generated internally The internal clock isn t very precise but for many applications it is sufficient An option exists to output the clock to a pin where its function can be verified using an oscilloscope In this exercise you will determine suitable values for hfuse and 1fuse such that the devices use the clock generated within the device and also output it to a pin where you will be able to verify that it is working as expected Note that the term fuse is left over from earlier programmable devices which really did have fuses which once blown were fixed in that state In newer devices the term refers to settings made in flash memory which can be reprogrammed multiple times by use of the programming hardware but importantly cannot be changed by the program running on the microntroller itself The factory default for hfuse is correct for what we require here but you will need to make one change to Ifuse For this exercise refer to the datasheet for the device at http Awww cl cam ac uk teaching 1314 P31 docs atmega644p pdf in particular sections 1 pin configurations 6 2 System clock and clock options and 24 2 Fuse bits and work out the required hexadecimal values for Ifuse and hfuse values to make the device e use the Calibrated Internal RC Oscillator e divide the clock by 8 e output the clock to a pin CHECK the values for Ifuse and hfuse with a demonstrator They will be used later Creating a directory struct
5. only need the brackets round 1 lt lt PB5 in the case 1 lt lt PB5 in order to define the operator precedence but it is good practice to put the brackets in anyway as it is easy to miss when editing code Copy of the template from template c http www cl cam ac uk teaching 1314 P31 code template c and put it in the directory structure you created earlier as exercise2 c If you need to rename the file after copying it then the linux mv command is the one you need In the header of your program add the following define F_CPU 1E6 1MHz include lt util delay_basic h gt include lt util delay h gt You now have access to the library functions _delay_ms J and_delay_us K where you subsitute double values for J and K which must be known at compile time You can t use variables for J and K if you try you will just get a very small or a very large delay See the documentation at avr libc http www nongnu org avr libc user manual modules html1 for more details One last step In order to loop forever rare in most C programs but common when using microcontrollers while 1 code in here you now have all the parts you need to write code to flash the LED once per second 10 Low Power and Embedded Systems Workbook 1 Modify the port_direction_inti function to assign PBO as an output Write a chunk of C code in the main function to flash an LED once per second In pseudo code it would be wh
6. 500 Tells avrdude the type of programmer being used e Erase the device before programming U hfuse w 0x99 m Perform a memory operation In this case hfuse write value to write immediate that is the value to write is literally the value 0x99 Low Power and Embedded Systems Workbook 1 Connections The next stage is to fit the microcontroller into the prototyping board and wire it up to a power supply and a programmer These devices can use In Circuit Programming i e the device does not need to be removed from the board in order to be programmed Note that Pin 1 of the device is marked with a dot and the pins are numbered counter clockwise when looking from above Refer to the circuit diagram http www cl cam ac uk teaching 1314 P31 docs breadboard_program pdf Connect the device up as shown in the diagram There is a photo showing one possible layout here http www cl cam ac uk teaching 1314 P31 docs programming_header jpg Important The 10uF tantalum capacitor is polarised It MUST be fitted the right way round Tantalum capacitors rely on a thin electrolytic film to achieve their high capacitance per unit volume and this film depends on the electric field generated by the applied voltage Connecting an electrolytic capacitor incorrectly can lead to the device exploding Apply 5 Volts from the PSU to the device the command to program the device fuses is make fuses The programming software carries out a read to ge
7. ed Circuit IC In these workbooks you will be using the ATMEGA644P microcontroller made by Atmel There are a large number of members of this family of microcontrollers each with different capabilities For the project part of the course other devices in the family may be a better fit to the requirements e A power supply PSU The early exercises need a PSU capable of delivering 5 V at 100mA Note that some members of the microcontroller family will work at reduced clock speeds at supplies down to 1 8 V In these first 4 weeks you will be using PSUs with a current limit When the output is switched on the display shows the current being drawn With the output off the displays the maximum current which can be drawn before the PSU cuts the supply voltage If the current is high compare with other people then there is invariably something wrong which you should investigate or ask a demonstrator for help Low Power and Embedded Systems Workbook 1 A programmer for the microcontroller these worksheets are written assuming the use of a USB based device from tuxgraphics org A prototyping board so we can develop the hardware sensors and interface circuits Software Toolchain avr gcc a C cross compiler An alternative would be to use an AVR cross assembler enabling us to write assembly code directly While an assembler might produce slightly faster and more compact code C should give reasonable results whilst being somewhat easie
8. ed to have completed each workbook before the start of the next session During the sessions demonstrators are available to assist you if you have any questions or if anything is not clear An on line version of this workbook is available at workbook1 htm http www cl cam ac uk teaching 1314 P31 workbook1 html You should check this page regularly for announcements and errata You might find it useful to refer to the on line version of this workbook in order to follow any provided web links or to cut and paste example code Low Power and Embedded Systems Workbook 1 Assessment You need to have obtained 4 ticks awarded for completion of each of the 4 workbooks You will also need to submit a formal report concerning your project work The report should be approximately 4 000 words in length and should be submitted to the Teaching Office on the first teaching day of the Lent Term Students are also encouraged to submit their lab books Document conventions Within these worksheets the following conventions will be used Important This style is used for information of particular importance This style is used for program listings Note that you can save yourself considerable amounts of typing by referring to the online version of this document and using cut and paste This style is used for instructions for you to follow When referring to the names of registers in the microcontroller or bit positions within registers a
9. emonstrator who will award a tick for each completed workbook In some instances you may need to provide completed C code When this is the case you are required to provide neatly formatted and commented code such that someone else could take your code and modify it without having to decipher cryptic comments or obscure syntax For everyone s sanity use the simplest and most readable way of carrying out the task there are no bonus points for clever but unreadable code There may be occasions eg for optimised speed where you need to use cunning optimisations and tricks If so comment them really well or the next programmer to see the code may well decide to make it more readable and break it That next programmer may well be you in 3 years time of course For the final 4 weeks you will be conducting your own design and build project There is a list of project suggestions available project_suggestions html http www cl cam ac uk teaching 1314 P31 project_suggestions html or project_suggestions pdf If you have any ideas which you think might be suitable for a project please discuss them with us at the earliest opportunity so that we can judge their feasibility make recommendations and order any specialist components You need to have a 1 page project proposal approved by a demonstrator prior to session 5 Work your way through the exercises in each workbook Once you have done this contact a demonstrator for ticking You are expect
10. fixed spaced font will be used This workbook was created using Docbook and transformed into pdf and html versions Supporting material All the following are available at http Awww cl cam ac uk teaching 1314 P31 or sub directories The online version of this workbook at http www cl cam ac uk teaching 131 4 P31 workbook1 htm allows you to follow the links easily template c http www cl cam ac uk teaching 1314 P31 code template c A template suggestion for C programs You may already have your own style for C programs in which case that would be a good choice The important things is to develop a consistent structure When designing with microcontrollers you will find that you re use existing code a great deal Having a structure to your programs will help to make code re use easier and less prone to errors for example forgetting to include initialisation code ATMEGA644P pdf Latest http www atmel com images atmel 801 1 8 bit avr microcontroller atmega164p 324p 644p_ datasheet pdf Local copy http www cl cam ac uk teaching 1314 P31 docs atmega644p pdf Data sheet for the Atmel ATMEGA644P microcontroller used in these exercises You will need to refer to this frequently Within these workbooks it will often be referred to as the datasheet The section numbers referred to in these workbooks refer to revision 8011Q of the datasheet dated 02 13 There are a number of devices with almost identical part numbers They
11. ile Set a suitable bit in the PORT register to output a 1 to the LED wait 0 5 second clear a suitable bit in the PORT register to output a 0 to the LE wait 0 5 second assuming you called this exercise2 c modify the Makefile to change exercise1 to exercise2 4 places Connect the programming header and issue the following commands make program You should be rewarded with a flashing LED If it isn t flashing but you think your code is correct you can look at pin 1 with an oscilloscope or multimeter to check Make sure you have shown your working code for each of the exercises to a demonstrator and received your tick Exercise 3 Before the class next week modify exercise 2 to use 2 LEDs flashing alternately Fit a red and a green LED to PORTB The green LEDs aren t as bright so turn the green LED on for 700mS off for 300mS but leave the red LED on off times at 500mS PB1 is being used for the clock output so add the second LED to a different pin on PORTB Finally Make sure you are completely familiar with the IO for the device that is the correct way to set the DDR and to read and write to ports The next workbook moves on to other topics and assumes a knowledge of this one Subsequent workbooks will not be as detailed as this one and cover a lot of material quite quickly This is particularly true for next week s workbook which has three exercises less so for week three which has two exercises To
12. is now available on dev tt yUSBO Depending on any other USB devices connected to the PC the programmer may be connected to dev ttyUSB1 or a higher number The Makefile cd to embedded_systems workboook1 exercise1 Create a file called Makefile using your favourite editor to read as below e Gedit is available and has C syntax highlighting turned on by default Line numbering can be switched on under Edit gt Preferences You might also want to turn on bracket matching and select a colour scheme which works on the LCD Emacs is available and also has syntax highlighting Switch on bracket matching in the Options menu Nano is installed start it from a command promp with nano To get C syntax highlighting type cat usr share nano c nanorc gt gt nanorc The name must be exactly as shown i e Upper case M the rest in lower case Edit the Makefile so that it contains the text shown on the next page To ease this process use cut and paste from the online version of this workbook at http www cl cam ac uk teaching 1314 P31 workbook1 html or right click and choose Save as from http www cl cam ac uk teaching 1 31 4 P31 code workbook1_ Makefile Note Makefiles use tabs not spaces for the whitespace preceding commands Check your Makefile as they may get changed to spaces during the copy process The contents of the Makefile will be explained in more detail later on For this exercise only the last two lines matter but
13. make best use of the time when demonstrators are available try to read through the next workbook and the relevant parts of the datasheet before the start of the session If there are parts which are not clear it will help you if you write a summary in the form of questions for the demonstrators while it is still fresh in your mind 12
14. ors then eventually all output files will be up to date The input files are more generally described as source files and the output files are described as object files During the processing by make the c files there may be several will be compiled and 1 inked with library object files to form object files ending in o These o files are converted in turn by make to a suitable format for the programming hardware usually with a hex extension The command make program invokes a program called avrdude which transfers the hex file to the microcontroller If the code transfers correctly the microcontroller restarts and executes the code immediately exactly as it would from power on Low Power and Embedded Systems Workbook 1 Exercises This week there are two exercises They are intended to be straightforward but they will provide a thorough test of the toolchain being used and give you a first taste of programming these microcontrollers in C These examples are also useful later on since they will enable you to verify the hardware and software toolchain when more complex programs that you have developed fail to work as expected Exercise 1 Setup the clock to the microcontroller and verify its function using an oscilloscope Exercise 2 Flash a light emitting diode LED once per second Exercise 1 Setting up the clock for the microcontroller The ATMEGA644P device can use one of several clock sources including one
15. provided for you the green and red ones For these devices the cathode is the shorter lead Connect it to Ground Connect the longer lead on the LED to PBO pin 1 on the ATMEGA644P Software In general it is a good idea to have structure in your programs For microcontrollers it makes a lot of sense to have building blocks which you can cut and paste between your different programs Microcontrollers don t have a vast amount of code space so you can t simply include all possible functions just in case you need them A suitable template is provided template c http www cl cam ac uk teaching 1314 P31 code template c Low Power and Embedded Systems Workbook 1 We have just seen the method used to assign ports as inputs and as outputs and how to read from and write to them When using microcontrollers it is often a requirement to set or clear one bit of a port at a time rather than writing a new value to the whole port The preferred way to set a bit is to use the operator For example bit 5 of PORTB PORTB 1 lt lt PB5 and to clear that bit PORTB amp 1 lt lt PB5 To explain this in more detail In the library header lt avr io h gt PB5 is defined as the value 5 So 1 lt lt PB5 is 00000001 shifted left 5 places to give 00100000 binary or 0x20 when expressed in hexadecimal PORTB 0x20 is equivalent to PORTB PORTB 0x20 and will set bit 5 leaving all others untouched We actually
16. r to program We will use the gcc cross compiler The cross prefix refers to the fact that we run it on one type of computer Intel x86 architecture but create code to run on a different architecture the Atmel device avr libc libraries for the Atmel AVR family of microcontrollers we are using Documentation is available at http www nongnu org avr libc binutils avr compiler tools such as make avrdude software to control the programmer Number notations Decimal numbers have no prefix and are shown as e g 45 Hexadecimal values are shown in the form O0xDF In these worksheets we will not use octal It is perfectly valid but is likely to cause errors The microcontrollers don t have floating point support Floating point number will be rounded without warning C Compiler Workflow In general each of the following steps need to be performed to create and run software on the microcontroller The C code is created in a file ending with the extension c A program called make is used together with a configuration Makefile make uses the timestamp on files and the contents of the Makefile to decide which commands need to be run make knows nothing about the compile process it simply compares timestamps on input and output files and runs a command if the input is newer than the output The resulting output file may be an input to another line in the Makefile and so the process may repeat multiple times If there are no err
17. t the device type a write to write the fuses then a read to verify the fuses for each of the fuses If all went well then you should be able to verify using an oscilloscope that there is a 1 MHz square wave on PORT PB1 which is pin 2 of the device If not the following list gives some common problems 1 No power to the microcontroller Note that the power consumption may be too small to low on the power supply current meter 2 The microcontroller is in the board the wrong way round 3 Not looking at the correct output pin 4 The oscilloscope probe ground clip is not connected to the board ground OV 5 Wrong values for hfuse and Ifuse if you get the value wrong and then can t program the device it may be that you have set it to use an external clock or have disabled programming Either way you ll need a new ATMEGA644P Exercise 2 Flash an LED So far you may not feel that much progress has been made but now we know that 1 The Atmel device is receiving power and using an internal clock 2 The in circuit programming is working 3 The software toolchain and at least the last 2 lines of the Makefile are correct In this exercise you will attach an LED to an output and write some C code to flash the LED To simplify this task a template is provided for you but some terms need to be defined first Low Power and Embedded Systems Workbook 1 Input Output Notation For a detailed description refer
18. to section 11 of the datasheet for the device The following is a brief summary Each 8 bit IO port is controlled by three 8 bit registers DDR Data Direction Register PORT data output register PIN data input register Different devices have different numbers of ports referred to as PORTA PORTB PORTC etc and controlled by DDRA DDRB DDRC etc DDR The 8 bit Data Direction Register DDR contains a 1 in each position where an output is required for example to set the top bit of PORTB PB7 as an output and the rest as inputs DDRB 0x80 PORT Assigning an 8 bit value to a PORT will write a value to the Data Output register If the corresponding pin is set to be an output then the value in the Data Output register will control the voltage on the output pin If the corresponding pin is set to be an input a 1 in the Data Output register will enable a pull up resistor on the pin To change fewer than 8 bits at once use the bitwise AND and bitwise OR functions in C see later in this section For example to set the top 5 bits to a low state the lower 3 bits to a high state PORTB 0x07 PIN PIN is used when reading from the data input register It shows the value from the pin on the device whether or not that pin is defined as an input or an output For example to read the values on the 8 pins PB7 PBO input_variable PINB Hardware For this exercise LEDs with suitable resistors built in for 5V operation are
19. ure to hold your work Many of the exercises in these worksheets will build on example code and on code created in previous exercises Creating a clear directory structure will help both you and the demonstrators For each exercise make a COPY of relevant files from previous exercises In some instances example code or partially completed code will be provided for you Log in to the computer and create a directory structure Commands are listed immediately below Use cut and paste if you can Low Power and Embedded Systems Workbook 1 eqs mkdir p embedded_systems workbookl exercisel mkdir p embedded_systems workbookl exercise2 mkdir p embedded_systems workbookl exercise3 mkdir p embedded_systems workbook2 exercisel mkdir p embedded_systems workbook2 exercise2 mkdir p embedded_systems workbook2 exercise3 mkdir p embedded_systems workbook3 exercisel mkdir p embedded_systems workbook3 exercise2 mkdir p embedded_systems workbook4 exercisel mkdir p embedded_systems workbook4 exercise2 cd embedded_systems workbook1l exercisel The Programmer Plug the programmer in to your PC and wait a few seconds for the PC to recognise that a new device has been connected Type dmesg One of the last few lines should be similar to ZSZS962 ARSIS wisi Sls WMD WSs Serial Davics Commeaiccsic MOW eicicevelaecl TO trEYyUSBO The key item here is the reference to tt yUSBO This programmer
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