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From: garyj@neptun.pcs.com (Gary Jennejohn)
Newsgroups: comp.sys.nsc.32k
Subject: MMU and disk
Message-ID: <9011080938.AA14922@neptun.pcs.com>
Date: 9 Nov 90 13:45:53 GMT
Sender: news@daver.bungi.com
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Approved: news@daver.bungi.com


Hi, Group!

Not having anything better to do, I decided to change the debugger so
that memory is mapped thru the MMU. I mapped the I/O regions with the
CI (cache inhibit) bit turned on.

All well and good, but I see strange behavior when I access the disk the
first 2 times. At the first access I always see a REQ timeout, at the
second access I see "can't initialize the disk" immediately. The third
and subsequent accesses work.

When the MMU is turned off I don't see any access problems. The disk
works first time every time.

Accesses to the duarts do not exhibit any strangenesses.

So, the question is, what's going on here? Why do I see this behavior only
when address translation is enabled? Does it maybe have something to do with
the fact that the ICU is already in a special memory region and is also being
cache inhibit-ed by the MMU? I haven't tried turning off the CI-bit for
the ICU yet.

Do any of you more experienced 32532-ers have any ideas? Is anyone else
using the MMU?

Gary