Re: Testing Sirius RAM card at 8MB?

[dempson@actrix.gen.nz (David Empson)]

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.

-- 
David Empson
dempson@actrix.gen.nz