Introduction to AVR Microcontroller Programming

The Atmel AVR family covers 8-bit and 32-bit microcontrollers with a compact instruction set that maps well to C. The chips are cheap, the toolchain is free (GCC-based), and a USB programmer like the USBasp lets you flash code in seconds. This post walks through setting up the Linux toolchain and flashing a first LED-blink program.

Packages required on Linux

• binutils-avr: assembler, linker, and object-file utilities targeting the AVR architecture.
• gcc-avr: the GNU C cross-compiler for AVR.
• avr-libc: C standard library, startup code, and header files for AVR targets.

Sample program: blink an LED

 1#include<avr/io.h>
 2#include<util/delay.h>
 3main()
 4{
 5
 6        DDRC |=1<<PC2;  /* PC2 will now be the output pin */
 7        while(1)
 8        {
 9                PORTC &= ~(1<<PC2);/* PC2 LOW */
10               _delay_ms(10);
11                PORTC |=(1<<PC2); /* PC2 HIGH */
12               _delay_ms(10);
13        }
14}

Save the above program to a file led.c.

Then compile the program using avr-gcc and convert the C code into object code:

1avr-gcc -mmcu=atmega8  led.c -o led.o

In the next step, convert the led.o object code to hex:

1avr-objcopy -j .text -j .data -O  ihex  led.o  led.hex

In the final step, use USBASP to write the program to the AVR:

1avrdude -c usbasp -p m8 -U flash:w:led.hex:a

For more details about USBASP, visit this guide.

Code explanation

The GNU C compiler for the Atmel family identifies all functional units within the microcontroller with meaningful names. Writing PORTC=0xff makes the compiler generate machine code that writes 0xff to I/O port C, setting all port C pins to logic high. Because ports are bidirectional, you must decide whether each pin should act as input or output. If the i-th bit of the DDRC register (data direction register C) is 1, the i-th pin of PORTC will be an output; otherwise it acts as an input. (Pin and bit numbers start at zero.) To blink an LED you drive a pin high, then low. Here we use PORTC’s 2nd port, PC2, which maps to physical pin 25. The _delay_ms() calls from <util/delay.h> insert a timed pause between the two states.