http://tuxgraphics.org/electronics

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Tuxgraphics AVR C-programming tutorial Abstract: This is an in introduction to programming of AVR microcontrollers using C as a language. The avr-gcc was originally developed for Unix systems. Today it is available for almost any system and very widely used. This article will therefore also cover Windows. The setup on a Mac is almost identical to Linux. _________________ _________________ _________________

Hardware becomes software

What are Microcontrollers?

What are AVR microcontrollers?

Let's start with a simple circuit

Blinking LED circuit, click for a PDF version

Programming the microcontroller

@echo -------- begin winload.bat --------

set PATH=c:\avrgcc\bin;c:\avrgcc\utils\bin
REM change the com-port as needed:
set CHIP=m8
avrdude -p %CHIP%  -c stk500v2 -P COM4 -e -U flash:w:ledtest_pre.hex

@echo --------  end  --------
pause

#!/bin/sh -x
# script to load code into a atmega8 (for Linux and Mac)
#
chip=m8
avrdude -p $chip -c stk500v2 -P /dev/ttyUSB0 -e -U flash:w:ledtest_pre.hex
# if you want to start it by double click in the file manager
# then uncomment the following line to keep the window open until
# you hit return:
# read

avrdude -p m8 -c stk500v2 -e -U flash:w:ledtest_pre.hex

avrdude: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.10s

avrdude: Device signature = 0x1e9307
avrdude: erasing chip
avrdude: reading input file "ledtest_pre.hex"
avrdude: input file ledtest_pre.hex auto detected as Intel Hex
avrdude: writing flash (158 bytes):

Writing | ################################################## | 100% 0.13s

avrdude: 158 bytes of flash written
avrdude: verifying flash memory against ledtest_pre.hex:
avrdude: load data flash data from input file ledtest_pre.hex:
avrdude: input file ledtest_pre.hex auto detected as Intel Hex
avrdude: input file ledtest_pre.hex contains 158 bytes
avrdude: reading on-chip flash data:

Reading | ################################################## | 100% 0.08s

avrdude: verifying ...
avrdude: 158 bytes of flash verified

avrdude: safemode: Fuses OK

avrdude done.  Thank you.

The software

int main(void)
{
          /* enable pin as output by setting the data direction register */
          DDRC|= (1<<DDC5);

          while (1) {
                      /* led on, pin=0 */
                      PORTC &= ~(1<<PORTC5);
                      delay_ms(500);
                      /* set output to 5V, LED off */
                      PORTC|= (1<<PORTC5);
                      delay_ms(500);
          }
          return(0);
}
    

• _delay_ms takes a max value of 262ms. So to delay 0.5 seconds one would need to write _delay_ms(250);_delay_ms(250);
• the main reason is however that _delay_ms makes the code very fat and you will quickly fill up the flash memory of your microcontroller just by calling that function a couple of times.

How do I compile that code?

avr-gcc -g -mmcu=atmega8 -Wall -Os -c ledtest.c

avr-gcc -g -mmcu=atmega8 -o ledtest.out -Wl,-Map,ledtest.map ledtest.o

avr-objcopy -R .eeprom -O ihex ledtest.out ledtest.hex

avr-size ledtest.out

Help! Give me an IDE

• http://www.crimsoneditor.com/ is a very powerful choice for windows.
• http://www.nedit.org/ is a good editor for Unix systems
• http://www.vim.org/ I like this one very much. It exists for Windows, Linux and Mac but you have to learn how to use it. Only after a couple of weeks training you will understand why I like it.
• http://www.gnu.org/software/emacs/windows/Getting-Emacs.html Emacs, a bit fat but very powerful and available for almost any system.

Makefiles

# comments start with a hash
#
target:  dependency1 dependency2 ...
<tab> command

# our main target:
ledtest.hex: ledtest.out
      avr-size ledtest.out
      avr-objcopy -R .eeprom -O ihex ledtest.out ledtest.hex
#
# now all the small intermediate things that we need:
ledtest.out: ledtest.o
      avr-gcc -g -mmcu=atmega8 -o ledtest.out -Wl,-Map,ledtest.map ledtest.o
#
#
ledtest.o: ledtest.c
      avr-gcc -g -mmcu=atmega8 -Wall -Os -c ledtest.c

@echo -------- begin winmake.bat --------

set AVR=c:\avrgcc

set CC=avr-gcc

set PATH=c:\avrgcc\bin;c:\avrgcc\utils\bin

make -f Makefile

@echo --------  end  --------
pause

What are Fuses?

avrdude -p m8 -c stk500v2 -v -q

This will then result in a big printout but the important lines are:

avrdude: Device signature = 0x1e9307
avrdude: safemode: lfuse reads as E1
avrdude: safemode: hfuse reads as D9

Debugging

Writing small and efficient code

• uint8_t (same as: unsigned char)
• int8_t (same as: signed char)

• uint16_t (same as: unsigned int)
• int16_t (same as: int)

Code examples

Code examples: Analog to digital conversion

// return an analog value for a given channel. Works without interrupt
unsigned int convertanalog(unsigned cha channel)
{
        // Use the intenal  ref:
        ADMUX=(1<<REFS1)|(1<<REFS0)|(channel & 0x0f);
        // set the clock division factor such that you
        //  stay in the recommended range of 50-200kHz
        ADCSR=(1<<ADEN)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0);
        //  start conversion
        ADCSR|= (1<<ADSC);
        while(bit_is_set(ADCSR,ADSC)); // wait for result
        adlow=ADCL; // read low first !!
        adhigh=ADCH;
        return((unsigned int)((adhigh<<8)|(adlow & 0xFF)));
}


// Copy/paste the above code and to read the voltage on ADC0 pin you would use:

adc0val=convertanalog(0);

Code examples: Timers

static volatile uint8_t cnt2step=0;

// this function gets now called in 20Hz intervals
ISR(TIMER2_COMP_vect){
        cnt2step++;
        if (cnt2step>=10){
                if (PORTC&(1<<PORTC5)){
                        LEDON;
                }else{
                        LEDOFF;
                }
                cnt2step=0;
        }
}

/* setup timer T2 as an interrupt generating time base.
* You must call once sei() in the main program */
void init_cnt2(void)
{
        cnt2step=0;
        TIMSK=(1<<OCIE2); // compare match on OCR2
        TCNT2=0;  // init counter
        OCR2=195; // value to compare against 3906Hz/195=20Hz
        // do not change any output pin, clear at compare match with OCR2:
        TCCR2=(1<<WGM21);
        // divide clock by 256: 1MHz/256=3906.25Hz
        // clock divider, start counter (or with WGM21 setting):
        TCCR2|=(1<<CS02)|(1<<CS01)|(0<<CS00);
}

int main(void)
{
        LED_INIT;
        LEDOFF;
        init_cnt2();
        sei();

        // nothing to do in the main loop:
        while (1) {
        }
        return(0);
}

Code examples: LCD displays

#include "lcd.h"

int main(void)
{
        // initialize display:
        lcd_init(LCD_DISP_ON);
        // go to position 6 in the second line (1):
        lcd_gotoxy(6,1);
        // write some text:
        lcd_puts("=OK=");
}

Conclusion

References/Download

• Download section
• Building your own avr-gcc environment with atmega328p capabilities, Linux, How to install a functioning AVR C-compiler. Includes links and hits for Mac and Windows. [now replaced by: Linux: AVR microcontroller programming in C and Windows: AVR microcontroller programming in C]
• avr-libc 1.6.4, modules, avr-libc documentation
• article from 2004 "Programming the AVR microcontroller with GCC, libc 1.0.4", this is the grandfather of this new article.
• The tuxgraphics electronics online shop (world wide shipping): shop.tuxgraphics.org
  
• http://www.fourwalledcubicle.com/AVRArticles.php, really good AVR tutorials by Dean Camera

2012-07-17, generated by tuxgrparser version 2.57