Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!ukc!axion!delluk!tim
From: tim@delluk.uucp (Tim Wright)
Newsgroups: comp.unix.i386
Subject: Re: > 16MB on ISA bus, with aha1542a
Message-ID: <tim.648722527@holly>
Date: 23 Jul 90 08:42:07 GMT
References: <654400008@cdp>
Sender: usenet@delluk.uucp (Usenet posting login)
Organization: Dell Computer Corp., Bracknell, UK
Lines: 33

In <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.

>I heard in this group of some parameters in the AT&T
>UNIX kernel "3.2...", that allocate kernel buffers
>to be used for DMA, when there is a request to DMA
>into memory in certain ranges.  Presumably, any
>3.2.* UNIX that has these parameters, is capable of
>disallowing DMA to memory over 16MB.  The parameters
>are called DMAEXCL and DMAABLEBUF.

>I am running Interactive 2.0.2, and it doesn't have
>DMAABLEBUF.  I wonder if the new release (2.0.2)
>does.

DMAABLEBUF and DMAEXCL are in the kernel. However the most important
thing is to change /etc/default/boot and alter/add the line
MEMRANGE=0-640KL0,1M-16128K:0,16M-128M:1
which I believe tells the kernel where DMAABLE memory is located - the
buffers parameter merely allocates some buffers to do DMA into if you
go outside this range. That at least is the way I understand it.
As you can see - we block out 640K to 1MB. I think MEMRANGE only
refers to whether or not the memory is DMAABLE but I'm sure someone
will correct me if I'm wrong :-)

Tim
--
Tim Wright, Unix Support               | Email: ...!ukc!delluk!tim
Dell Computer Corp. (UK), Bracknell    | (pending domain registration).