Subject: Re: Return of "D'oh"
To: Source Librarian <>
From: Chris G. Demetriou <>
List: current-users
Date: 08/01/1994 13:03:05
> Our little test -current machine is running pretty well -- it hasn't crashed
> once. However, we are getting some ominous messages in our syslog file
> (/var/log/messages). Once in a while, the aha driver tells us:
> Aug  1 08:45:19 news /netbsd: aha0: DMA beyond end of ISA
> We first thought it had to do with us having 20mb of RAM in the machine, so
> we pulled 4mb out to make it 16mb, but we're still getting the message. We
> then tried recompiling the kernel with other options, and it happened again
> this morning. Is this a serious problem?

When booting, what does the BIOS say for the amount of memory
you have in the system?  what do the boot blocks say?  what does
'dmesg' say?

my guess is that your bios/firmware is 'smart', and, if you aren't
using RAM to shadow the 384k I/O hole, it remaps it so that it's
at MEM+0 -> MEM+384k, where MEM is the amount of RAM you have in your
machine (i.e. 16M).

This means that you _do_ have usable memory above 16M, and since ISA
DMA only works in the first 16M, things might not work right...
(in particular, normal i/o should work fine, but all 'raw' i/o,
i.e. dump/restore from tape, fsck, etc., may not work.  note that the
fsck at boot (because of the way memory is allocated) will probably
work just fine, but later ones, e.g. in /etc/daily, may not work, and
may corrupt other blocks of memory.)

If you have a bios option to turn the remapping off, i suggest you try
it.  The generic solution is bounce buffers, but it's not going to
get done today.  8-)