Better keep to the specifications. ISA is 5 V in all cases, even thoe 3,3 V logic is accepted at input. Any FPGA must tolerate 5 V from ISA cards. And PCI is nice but it is timing tricky and I/O heavy.
5V is not that big of a deal.
http://users.ece.gatech.edu/~hamblen/UP3/IDTQS3384AN.pdfhttp://www.xilinx.com/support/documentation/application_notes/xapp646.pdfhttp://www.altera.com/literature/an/an330.pdfIf the person designing the board can't get PCI timing right, then I wouldn't be very optimistic about the other things either... This would require someone that knows how to do this stuff properly with or without PCI.
And in the big-boxes, consider at least one slot having a PCI to PCI-Express bridge to a x16 plastic slot to hold a modern graphics card, even if it's only a x1 slot electronically running at PCI bus speed. (yes, that bridge chip adds cost)
Though I guess some people might want to continue using brigeboards or Goldengate ISA bridges and their collection of ISA cards. Did they do PCI to allow the user's option of a rear bracket holding EITHER an IDA card or a PCI card? Maybe do both, FPGA pins permitting of course.
http://www.kids-online.net/learn/click/details/sharedpi.htmlBy loading the correct image you can downgrade at will.
I was thinking more along the lines of putting an A3000/4000 style CPU slot on the A2000 replacement motherboard instead of an A2000 style CPU slot. (or if you're crazy enough and have enough FPGA pins, both) Then it could have a CSPPC card and run OS4 as well as get AGA etc.
This will likely increase cost in a non-benefitial way. Better to use plain junk PC for such uses.
A slot and some wires, should FPGA pins allow? OK, depending on version of MMX slot it'd require a PCI-Express IO capable FPGA. And someone to make a PCI-Express logic to drive it. Or perhaps a PCI to PCI-Express bridge chip from PLX etc. But leave the slot empty and leave it to user to choose to put something there... If I was the designer, I'd consider the possibility of modern graphics card in A500, A600, A1200, A1000 even, as a desirable possibility.
What we really need is a proper production run of Amiga keyboards that plug into USB or ps2.
It'd be easier/cheaper to make the reverse of the adapters allowing standard PC keyboards to work in Classic Amiga motherboards. Then use an existing Classic Amiga keyboard.
Speaking of keyboards/mice, I'd try to design things so that these replacement motherboards can take at least PS/2 with a direct pin adaptor, not to need the special Amiga protocol adapters. Not sure if there is a direct mouse pin adapter that would fit an Amiga mouse port to design toward, may need the special Amiga adaptor to PS/2 mouse, or perhaps a not done before direct pin adaptor can be done and move protocol part into FPGA, cheaper than special protocol adapters we have now? Someone else already provides PS/2 port to USB keyboard/mouse adaptors.
Also, if not an Amiga style accelerator slot, then consider making the motherboard a Com-Express carrier and mux outputs of that with FPGA outputs. (And FPGAs still on their own standard modules to the new motherboards) There's modern PowerPC modules for that standard. While they are not supported in OS4 now, maybe we can get there, and have as modern stuff in our Classic cases as we can get. And motherboard is still a relatively simple PCB doing little more than connections and close-to-port electronics (serial port level shifters, video D/As, analog D/As, etc.)
I just think that if you're going to the trouble to make a replacement for a Classic motherboard, then give it some modern update options where it makes sense to do so. I think that going to this effort and leaving out PCI would be an odd choice.
