Excel makes quick work of such tasks!

Also Prahlad's suggestion of using a pca timer for the phase control should only require 1 capture and 1 compare channel on a speedy '51 - I do many channels of phase control dimming this way. Prahlads method of resetting the timer on a zero cross requires that the zero cross signal is well filtered andactually occurs at zero crossing. What I do is use the zero cross input to correct an the internal half phase timer - that way you can apply some filtering of the zero cross signal internally so it ignores mains noise.