Matthew Carpenter <superpsycho@comcast.net> wrote:
I've got an 8MB RAM sirius RAM card installed and I'm beginning to think
that something isn't quite right... My iigs seems to puke on read if I
try to copy larger files or a lot of files at once.
What SCSI card are you using? An Apple High-speed SCSI card can only
support DMA within the first 4 MB of a memory expansion card, due to a
design limitation of the FPI/CYA chip on the IIgs motherboard: it only
supplies two row select signals to the memory expansion slot, and
doesn't supply the bank address during a DMA cycle.
If you have a memory card with more than four rows (4 MB) then a DMA
cycle might access the first or second block of rows on the card,
resulting in DMA cycles randomly accessing the wrong memory locations.
Not good.
The third-party RAMFast SCSI card got around this limit.