HEI Ignition Coils

About dwell overlap, I use separate process with another timer, predict dwell based on next RPM, calculation for each event. A bit like dual points, one process charges coil, another opens for ignition. Both timers share same clock. Interrupts are used, routines very short. Calculations done with integer math, outside of interrupt routines. A logic analyser is used to verify all timings, using i/o pins. I also employ watch dog coil power down for loss of distributor signal for > 0.3s.