The timer approach which does not use interrupt would solve the problem of interrupt latency. However, since my firmware has multiple tasks to perform besides generating a constant square wave, there is no way to wait in the endless loop.

I think the only solution is by generating the square wave through XTAL2 without requiring any timer operation.

If the frequency of the square wave is much slower, says 100Hz, then maybe we can use a timer interrupt.

:)

Regards,
Ivan