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From: brian@anorak.coverform.lan (Brian Somers)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: DMA
Date: 20 Nov 1996 21:32:22 -0000
Organization: Coverform Ltd.
Lines: 32
Sender: brian@awfulhak.demon.co.uk
Message-ID: <56vtd6$1mo@anorak.coverform.lan>
References: <328C8861.48A3@mercurio.uc.pt> <56mjnr$b4a@uriah.heep.sax.de>
<329083AC.7048@mercurio.uc.pt>
Reply-To: brian%anorak.coverform.lan@awfulhak.demon.co.uk
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In article <329083AC.7048@mercurio.uc.pt>,
Filipe Araujo <filipius@mercurio.uc.pt> writes:
:
: I believe I must follow these steps:
:
: - allocate contiguous memory under 16 MB;
: - give the physical addresses (and sizes) to the adapter;
: - lock the corresponding pages in central memory (how?);
:
: The adapter is now able to perform DMA.
: Is this correct?
:
: Thank you very much.
As J"org already said, there's no 16Mb limit on a PCI bus - btw, does
anyone know how many usable address lines a PCI bus has ?
The second point, I'm fairly sure, is correct and I assume that the
third point (question) is saying "how do I make sure that physical
memory isn't used for anything else". I *think* you should use
kvm_alloc(). I'm no kernel hacker, but it seems that this allocates
the memory (returning a virtual pointer) and you can then use the
KVTOPHYS() macro to get a physical address to give to the hardware.
Of course, I've never hacked in places like this, so I apologise if
I send you on a wild-goose-chase :-()
--
Brian <brian%anorak.coverform.lan@awfulhak.demon.co.uk>
<http://www.awfulhak.demon.co.uk/>
Don't _EVER_ lose your sense of humour....
.