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From: Peter Dufault <dufault@hda.com>
Message-Id: <199710271303.IAA24466@hda.hda.com>
Subject: Re: mmap/mlock problem
In-Reply-To: <199710271231.NAA03303@gil.physik.rwth-aachen.de> from Christoph Kukulies at "Oct 27, 97 01:31:56 pm"
To: kuku@gilberto.physik.RWTH-Aachen.DE (Christoph Kukulies)
Date: Mon, 27 Oct 1997 08:02:59 -0500 (EST)
Cc: freebsd-hackers@freefall.FreeBSD.org
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> The ISA mapped memory is a dual ported RAM which is 
> controlled by the on board CPU on one end and the
> user process on the other end. Writing something
> into the ISA memory should not result in reading
> the same back from it. But the fact of the matter is
> that I read back what I'v written into it and this
> seems to me as if the memory is cached.
> 
> I tried a mlock call on the mmapped region but this
> seems to fail in the user process.

You shouldn't have to lock the region - the page tables for that
virtual section of your process are set up to map to those physical
addresses.  Unplug the board and verify that you now can't write
to it so you know you're accessing the board - I think the map
will still succeed.

Do you have to do some sort of hand shake with the CPU on the
I/O board?

Peter

-- 
Peter Dufault (dufault@hda.com)   Realtime development, Machine control,
HD Associates, Inc.               Safety critical systems, Agency approval