- Fit in a footprint that will allow the keyboard and PSU to be fitted and the case closed;
- Switch to 4 layer board;
- Work reliably at 50MHz (ideally driving the RAM at 100MHz, like the TF536).
One XC95288XL 144-pin CPLD (currently in use on my first, heavily modified, rev3 board which runs at 50MHz) currently costs around £20. I've managed to squeeze a cut-down firmware into an XC95144XL (£10) for my second rev3 (unmodified & can only handle 40MHz -- poor clock lines?). But this is extremely restricted.
To me one £10 144 CPLD to handle SDRAM and address decoding and one £5 72 CPLD to handle the bus and perhaps service a register or two seems like better value in terms of capability and risk (blowing any one up is cheaper!) but it does add complexity.
What do you guys think? Is keeping the two playing nicely together harder than I imagine?