Analogue-sequencer

I forgot I changed the P3 cock to 18Mhz... which means the clock period
resolution is in steps of 0.666 microseconds, and the minimum tempo is
therefore about 30 bpm.

I'm having play with some integer maths to see if I can calculate timer
values on the fly from a 16 bit tempo.
Maybe I can remove the lookup table altogether, and make the resolution
much finer...

Cheers,
Colin f