Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!snorkelwacker!bloom-beacon!eru!luth!sunic!mcsun!hp4nl!tuegate.tue.nl!tuewsd!wsinpdb
From: wsinpdb@lso.win.tue.nl (Paul de Bra)
Newsgroups: comp.unix.i386
Subject: Re: > 16MB on ISA bus, with aha1542a
Message-ID: <1297@tuewsd.win.tue.nl>
Date: 18 Jul 90 08:23:03 GMT
References: <654400008@cdp>
Sender: wsinpdb@win.tue.nl (Paul de Bra)
Organization: Eindhoven University of Technology, The Netherlands
Lines: 26

In article <654400008@cdp> steve@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@research.att.com)