AVR For PIC People, Part 1: The Basics

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.

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.


About Steve

When it comes to the desktop, Steve is a former Amiga, Windows, and Linux user, and as of six years ago, a die-hard Mac head (who, for once, isn't thinking of changing platforms again any time soon). When it comes to the server, Linux is pretty much the only game he plays. He also enjoys hardware hacking, and shouldn't be allowed near a keyboard after the sun sets (or for that matter, after it rises. Don't say I didn't warn you).
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2 Responses to AVR For PIC People, Part 1: The Basics

  1. Daniel says:

    Thanks for this! I’ve been using microchip’s PICs a fair amount, and wanted to start trying AVRs to see if they might be more simple. This will be a nice starting point.

  2. Steve says:

    Um. This is a serious cliffhanger – or did Part2 get blown with the wind^Wfuse? Is there still hope?
    Thanks anyway for the nice introduction, as a late adopter I appreciate it a lot. Everyone else is using RasPis now, but AVRs are fun for someone who decades ago had to learn and write (mainframe) assembly code!

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