Thank you, I have never heard of DDS before but it looks exactly like what I was looking for.
The thing is, I'm looking at frequencies of 90KHz for one drive (11us period) and 325KHz for another(3us period).
When I tried ISR based generation at 90KHz, I had some visible jitter on the waveform whereas it was rock solid for PWM output. That is mainly why I was looking at PWM-based generation.
Responding to an ISR in 11 (or 3!) us looks like it`s almost impossible, I can forget about digitalWrite for sure! Especially since I will be communicating with a serial port to respond to commands, that might be the opportunity to look at ARM Cortex chips( even the Maple).
Any further suggestions?
thank you again