> 16MB on ISA bus, with aha1542a

[Paul de Bra]

In article <654400008 at cdp> steve at cdp.UUCP writes:
>I am trying to run over 16MB on an ISA bus machine
>(that holds 24MB).  We use an adaptek aha1542a SCSI
>controller, and realize that it cannot DMA into
>memory over 16MB.
>
>...3.2.* UNIX that has these parameters, is capable of
>disallowing DMA to memory over 16MB.  The parameters
>are called DMAEXCL and DMAABLEBUF.

DMAEXCL is for a different kind of brain-damage (not being able
to handle more than one dma operation at the same time)

DMAABLEBUF already exists in AT&T Unix sVr3.2 (the docs i have are
for 3.2 release 2.0, so preceding 3.2.1 and 3.2.2). I don't know
about sVr3.1 anymore.

It is not surprising that AT&T added something for DMA to memory
above 16M early on because the AT&T 6386 (the original olivetti ones)
can hold 48 Mbytes of ram.

I have no idea why any of the other Unix vendors would omit this
capability.

Paul.
(debra at research.att.com)