One change that I will need to do this time will be to completely rewrite the tone-generating function. Originally, I just used whatever was available in the Arduino core that I used -- and that turns out to be quite a bit of code. Way over the 1k limit.

But hey, generating a PWM signal at a specified frequency while the microcontroller doesn't have anything else to do is not rocket science, right? Even if I completely fail to understand the timers, in the worst case I can just have a bunch of empty loops spinning there, busy-waiting for the right moment to flip the pin.

I didn't have much time today to do any actual experiments with the ATtiny85, but I did find an interesting article about a technique, that will maybe let me do a much better thing than a square wave: http://www.technoblogy.com/show?QVN