The Compiler And Support Software

And here, ladies and gentlemen, is the solution for Microchip’s ugly 8-bit compiler problem!  Atmel themselves supply a gcc-based toolchain for the AVR series, and it’s readily available for most platforms.  As I said a long while ago:  gcc FTW!

I am, however, far too lazy to build gcc myself under OS X (let alone track down all the appropriate patches for the latest AVR parts), and Atmel doesn’t offer a bundle for the Mac; only Windows and Linux.

Enter CrossPack: it’s gcc, avrdude, and a couple of other things, all nicely bundled for you in an OS X installer package.  I used the latest build, and it appears to support even the newest XMEGA chips, which is perfect.  Simply download the package, double-click, and install.  Piece of cake.

Oh, and you might want to add /usr/local/CrossPack-AVR/bin to your PATH; it makes life much simpler.

The Test Program

For the first time out, I really didn’t want to deal with anything complex.  Like so many test hacks, the goal was simple:  cause the LEDs to blink in alternating fashion.  This is easy to do, and usually a good first test when you’re playing with a new MCU architecture; it provides end-to-end verification of your toolchain (software and hardware) without getting complex.

After a bit of googling on the specific workings of the AVR, I came up with this:

#include <avr/io.h>
#include <util/delay.h>

int main() {
  // Set pins 3 and 4 of PORTB to output
  DDRB = (1<<PB3) | (1<<PB4);

  // Set the initial value for PORTB (pin3 high, pin4 low)
  PORTB = (1<<PB3);

  for (;;) {
    // Invert bits 3 and 4 in PORTB
    PORTB ^= ((1<<PB3)|(1<<PB4));

    // Delay for a quarter second.
    _delay_ms(250)
  }
}

Piece of cake, at least mostly.  The only catch is that _delay_ms() is a macro that requires the constant F_CPU, which must be set to the selected operating frequency of the AVR.  I do this on the compiler’s command line, like so (for the default fuse settings of 1.2MHz):

$ avr-gcc -mmcu=attiny13a -Os -DF_CPU=1200000 -o main.elf main.c

You can readily see the command-line definition of the F_CPU constant.  The -Os option causes the compiler’s optimizer to produce the smallest code possible.  The meaning of the -mmcu=attiny13a option should be self-evident:  it tells the compiler which AVR to target.

Boom.  Compiled Program.

Right?