I did do a lot of simulation of the logic. I built models of the hardware in software (C++).
But I didn't do any analog simulation, which was a mistake. I was aware of SPICE and had a look around but the tools I found seemed expensive. It was only after I'd started that someone pointed me at some free versions, LTSPICE in particular.
Why is analog simulation needed? Is it mostly for timing issues? Did you have to use any passive components in your design (like resistors or capacitors)?
A couple of reasons. Firstly its dynamic behaviour, If I'd known about the 1us gate propagation time earlier I may have tweaked the componentry a bit. The second reason is that it may have picked up some of my mistakes such as transposing the outputs or missing off some pullup resistors.
