Re: FS: Apple HS SCSI card Utility Disks

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

<cshank@freenet.edmonton.ab.ca> wrote:

> On 26 Aug 1996, Will Baguhn wrote:
> 
> > Sorting through my stack of disks, I found the two High-speed
> > SCSI Card utility disks.  The first one has the various partitioning
> > and formatting and whatnot utilities; the second has GS/OS drivers
> > for Scanner and Tape Backup.  $5, I'll mail 'em to ya.
> > 
> > The disks seem to be OK, just useless to me since I have a RamFast.
> > Someone had been looking for them, I believe.
> 
> I gather the High Speed SCSI Card's DMA feature is not supported by the
> RamFAST card.

I don't understand what you mean.  Are you wondering whether the RamFAST
supports DMA?  (It does, and it can be turned off if your system is not
DMA-compatible for some reason.)

The two main reasons for DMA not working are:

1. Your memory card doesn't support it.  What card do you have?

2. There is another card in the system which uses DMA, and the two are
conflicting.

The IIgs cannot support "background" DMA and another DMA device
simultaneously.  It is possible to use multiple devices that perform DMA
transfers synchronously (e.g. during an I/O call to the operating
system).  For example, you can have more than one Apple High-Speed SCSI
card installed in the same machine, with DMA enabled on all cards.

> I always wondered why my GS would crash when booting with 
> DMA enabled. IF I am correct in this, which RAM cards do support DMA?

All cards with a "standard" configuration: one, two or four rows of
256KB or 1MB (256KB, 512KB or 1MB using 256KB chips; 1MB, 2MB or 4MB
using 1MB chips) should support DMA.

Some cards with unusual configurations are able to support DMA, but
there are notable exceptions, particularly with earlier cards.  I think
the original Applied Engineering GS-RAM and GS-RAM Plus are not DMA
compatible (possibly only in some configurations).

The MDIdeas OctoRAM is an interesting case.  If you set it up for one,
two or four SIMMs, then it is DMA compatible.  It is not DMA compatible
if you set it up for eight SIMMs (but it probably works as long as all
DMA accesses are limited to the lower 4 MB).

Also note that the RamFAST claims to be able to support DMA with any
IIgs memory card, even ones that are not compatible with other DMA
devices.

-- 
David Empson
dempson@actrix.gen.nz
Snail Mail: P.O. Box 27-103, Wellington, New Zealand