Robert Boucher wrote:
I have used a IIe with an 8 meg Zip Chip for many years. The slot assignments are: slot 7 CFFA cardslot 6 1 meg Ramfactor card slot 5 high speed SCSI card to a Zip drive slot 4 Timemaster HO clock card slot 2 parallel printer cardI thought I had always had all slot speeds set for "fast". Several days ago I could no longer write to the SCSI card although Copy II+ could catalog and format the disk. I swapped cards around, etc with no luck. I finally set the SCSI card slot speed to normal and everything is working again.Has something happened to my computer, or is my memory wrong and this slot speed has always been normal?
Doesn't the Apple "High-Speed" SCSI card use DMA transfers by default? If it ever worked with a caching accelerator like the ZipChip, then there must be an alternative mode based on a software loop. Perhaps something is preventing the card firmware from properly switching over?
I'm certain that the Ramfast SCSI adapter (for example) probed for the presence of a ZipChip at startup and dropped back to polled I/O if one was found. Years ago, following a suggestion from Drew Vogan (RF designer), I hacked the RF firmware to dynamically inject a small transfer loop into the stack page prior to each IO operation. Turns out that the ZipChip always accesses the stack page at a faster rate than it does main memory - even with the RF slot set at "fast". IIRC, the controller benchmarked about 15-20% faster with the updated firmware.
I'll take a look and see if I can find a binary or hex image of the updated ROM.
Steve