Sat Jun 6 11:24:36 CEST 2009

bitbanged serial

So it looks like daisy-chaining should be feasible.  However, I'm
actually more interested right now in getting bitbanged serial to
work.  Both for debugging and for MIDI apps.

It doesn't seem to hard to have a single channel going, but how do you
do multiple?  Looks like busy-looping + oversampling is the best
approach.  This way each channel can have its own phase counter.

Now since I'm just playing anyway, maybe the E2 protocol should be
revived?  A low-bandwidth single channel 4-phase protocol:


3     provides power
3->4  is the sync edge
1     write time
2     read time

I did have some trouble to get this to work though.. What might be
better indeed is a simple modulated serial line.  This would allow
standard receiver hardware to work with just a modification to receive
and transmit to (de)modulate the signal.  The idle signal should be
encoded such that frame errors can be detected when you plug into an
active line.  Luckily idle=1 so this should be no problem.  Simply
using the odd / even bits should work.