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From: michaelv@MindBender.HeadCandy.com (Michael L. VanLoon)
Newsgroups: comp.unix.bsd.netbsd.misc
Subject: Re: sd0: DMA beyond ISA whazzat?
Date: 23 Nov 1995 05:19:45 GMT
Organization: HeadCandy Associates... Sweets for the lobes.
Lines: 41
Message-ID: <MICHAELV.95Nov22211945@MindBender.HeadCandy.com>
References: <48snme$1p1g@info4.rus.uni-stuttgart.de> <48uqpa$j5j@serpens.rhein.de>
NNTP-Posting-Host: mindbender.seanet.com
In-reply-to: mlelstv@serpens.rhein.de's message of 22 Nov 1995 10:33:30 +0100
In article <48uqpa$j5j@serpens.rhein.de> mlelstv@serpens.rhein.de (Michael van Elst) writes:
schweikh@zeiss.ito.uni-stuttgart.de (Jens Schweikhardt) writes:
>recently while compiling a new kernel (i386) I got the following
>messages:
> sd0: DMA beyond ISA
NetBSD 1.0 does not implement bounce buffers to fix hardware limits.
NetBSD 1.1 does implement bounce buffers for some (all ?) drivers
that need them.
This is incorrect. It only does this for devices that use the
motherboard DMA chips. DMA initiated on the far side of the ISA bus
(i. e. on a peripheral) is impossible above 16MB. NetBSD does not yet
have bounce-buffer support for this.
Once again, your options are to 1) take some memory out of the
machine, 2) build a kernel with a 16MB memory limit hard-wired, so you
don't have to physically remove RAM, 3) buy a SCSI card that uses a
real 32-bit bus (which has many substantial benefits besides this one,
not the least of which is vastly increased throughput), or 4) run a
different OS.
NetBSD *will* get ISA bounce-buffers some day. It is still being
debated exactly how such a thing would have to be implemented,
however. NetBSD runs on more architectures than any commercial
mainstream OS, and has to support all of them. ISA busses don't exist
only in PCs. For example, some DEC Alpha boxes are capable of
supporting multiple ISA busses (in addition to PCI and EISA), making
the picture even more contorted. The bottom line is that it's not as
simple a fix as the FreeBSD and Linux folks have been blessed with.
--
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Michael L. VanLoon michaelv@HeadCandy.com
--< Free your mind and your machine -- NetBSD free un*x >--
NetBSD working ports: 386+PC, Mac 68k, Amiga, HP300, Sun3, Sun4,
DEC PMAX (MIPS), DEC Alpha, PC532
NetBSD ports in progress: VAX, Atari 68k, others...
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