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From: Filipe Araujo <filipius@mercurio.uc.pt>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: DMA
Date: Thu, 21 Nov 1996 15:58:20 +0100
Organization: Lab. Redes de Alta Velocidade - DEE - FCTUC
Lines: 45
Message-ID: <32946E0C.EF5@mercurio.uc.pt>
References: <328C8861.48A3@mercurio.uc.pt> <56mjnr$b4a@uriah.heep.sax.de>
<329083AC.7048@mercurio.uc.pt> <56vtd6$1mo@anorak.coverform.lan>
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Hello,
Brian Somers wrote:
> In article <329083AC.7048@mercurio.uc.pt>,
> Filipe Araujo <filipius@mercurio.uc.pt> writes:
> : ...
> : - 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?
> 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 PCI local bus has 32 bits for addressing. The PCI local bus
specification also defines a transparent extension to 64 bits. The same
thing for data, because data and address lines are shared.
>
> 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.
I didn't find the function kvm_alloc()...
I found a function with a very interesting name: vm_page_alloc_contig().
Does anyone know if it can be used to allocate contiguous memory? If so, do
I still need to lock it in memory?
>
> Of course, I've never hacked in places like this, so I apologise if
> I send you on a wild-goose-chase :-()
No problem. All kinds of help are wellcome.
Regards,
Filipe Machado de Araujo
Departamento de Engenharia de Informatica
Faculdade de Ciencias e Tecnologia
Universidade de Coimbra
Portugal