After an Easter weekend spent mostly debugging circuits and sleeping, I finally have blinking LEDs - about three hour shifts after I probably should have gone to bed...

Anyway, the biggest problem I faced was the PIO not working. In the end, I used a CPLD dev board I had handy to make a simple latch, figuring it would be easier to debug the IO writes with that. After some playing around, I finally remembered that The high half of the address bus on IO reads/writes actually comes from other registers. I tweaked the address decoder to ignore the high bits on IO activity and it worked! Even better, when I went back to the PIO it was working too! 

I’m not sure I have input sorted yet but it’s certainly progress.

I already have a pile of small improvements (and some not so small) that I would like to make to the circuit so I’ll be exploring those ideas soon.