... but (afaik) chipset limitations put the real life maximum performance to about 25MB/s. Typical real life performance is somewhere around ~20MB/s.
For 20MB/s you will need to break some timings, especially on the /DTACK signal to get fast. This may work with many CPU card, or not. Write accesses are no problem with today's logic, but reads are, especially if you go for synchronous designs (see below).
I would not expect more than 15MB/s from a real life Zorro III card. With old chipsets and logic you can reliably do asynchronous designs, yielding in high speed (and the danger of spikes, too).
With modern high speed logic and I/O chips you will have to go for synchronous designs. Simply as new chips will accept even small spikes as /RD or /WR signals, so you will need quite some amount of synchronization logic (which Dave Haynie did mention already in the BigRAM documentation - "metastability").
Which means that synchronisation will cost extra time, but this can't be avoided if you want a stable system.
Next problem is that almost no CPU card (> 030 CPU) does support burst accesses on Zorro III. I have seen only 030 CPUs doing burst accesses up to now on Zorro III.
So you can't utilize the Zorro III burst mode which may give you extra performance.
Michael
