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I think that FW352 is the working "original" version and FW523 is the working "optimised" version
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Yes, that's right
The initial release version worked quite well but Karen found a bug in the 'inverse' feature which is fixed in FW352. At this point the code worked equally well with both 877 and 877A, although it did slow down the host system to a very significant extent.
FW523 is the first 'optimised' one after Karen had spotted and fixed that Port-A problem, after which all memory locations started to be rendered correctly to the screen, however, from the first optimised version onwards there was a new 'shudder' problem in graphics mode only and with the 877A chip only.
All subsequent versions after FW523 were aimed at either fixing the graphics shudder problem (for 877A chip only) or fixing the occasional memory corruption problem, but were unfortunately unsuccessful, although of course we were grateful to Karen for trying.
I would suggest that FW523 would be the best one to work on if you are thinking of extensively commenting the code because later versions have bits added in which Karen hoped would solve problems - leaving these in will just make it more complicated than it needs to be.
The graphics shudder problem has, we all seem to agree, been solved by specifying that only the plain 877 can be used. Trying to solve it for the 877A was taking up too much of Karen's time and energy.
This leaves the 'occasional memory corruption' problem which we are now hopeful can be 'solved' at least initially by adding 47pF capacitors to the high address lines. It may be possible to fix it 'properly' by making timing adjustments or changing the order of certain events in firmware.
I think that by posting the code -and- the source here Karen implicitly expected that we would take it and run with it as long as she is credited with the firmware and hardware design, of course.
Karen has not posted here herself since the last day of October, although I hope she has been able to follow what we have been trying to do. If Tim / Mark's little hardware bodge works for me as well, then we will be able to say that Karen's VDU works even better - produces a cleaner, nicer image than the SOC VDU and slows down the host system even less than the SOC VDU.