The patient is well again !

From top to bottom: a) Interrupt servicing the LED drivers with PWM pulses. It only runs when the edges need to change and takes very little time. But it is crucial that its timing is 100% spot on. b) LED driver enable signal produced by the ISR. c) pin-change interrupt that reads incoming serial data @9600. d) pulses indicate when the bit are sampled, which is tuned by inserting fixed delays. e) incoming serial data. f) status LED showing something I can't remember right now.