AVR-Chat

----- Original Message ----- 
From: "Marc R.J. Brevoort" <mrjb@dnd.utwente.nl>
To: <AVR-Chat@yahoogroups.com>
Sent: Tuesday, December 29, 2009 9:02 PM
Subject: Re: [AVR-Chat] Re: ATtiny2313 audio- w/source


> Hi Donald,
>
>> Please understand the basics of what you want to do, then code.
>> I think this may help you.
>> http://www.avr-asm-tutorial.net/avr_en/AVR_DAC.html
>
> Thanks for the link. Unfortunately it has little to do with my main
> issue, which was about how to write timer-based, interrupt-driven
> code for the AVR in C. The actual signal generation (as described
> in the above article) is the easy part!
>
> I find it interesting, however, that the code on the page you mentioned
> seems to have limits similar to the ones I have been running into:
> 1800Hz for a 256-sample sine wave at a 4MHz clock speed translates to
> roughly 61 cycles per sample, which does not leave a lot of room for
> anything else. (In an interrupt-driven solution, a few more cycles are
> burnt to preserve machine state).
>
> It does leave me curious about how Leon managed to generate 200kHz
> sine waves on a 12 MHz AVR- that would seem to only leave 30 cycles
> per sample (and at that point the signal would really be a square wave
> rather than a sine wave).
>
> Unless there was some other hardware-assisted trick at work there.
> The question is if that 'trick' would be of any help for polyphonic
> audio.
>
> Leon, care to comment?

The code is here:

http://webspace.webring.com/people/jl/leon_heller/dds.html

I've got a similar program that is interrupt-driven, avoiding glitches when 
the frequency is changed.

Leon