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Re: How to the the physical addresses under linux (au1500)

Subject: Re: How to the the physical addresses under linux (au1500)
From: Sergio Ruiz <>
Date: Tue, 3 May 2005 23:04:41 +0200
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Reply-to: Sergio Ruiz <>
On 5/3/05, Dan Malek <> wrote:
> On May 3, 2005, at 3:56 PM, Sergio Ruiz wrote:
> > I am trying to program  the DMA (with the ac97) in assembler using a
> > linux kernel module for mips teaching purposes.
> I think you want to choose a more simple teaching example :-)

Well, in fact we are two the students, the teacher gave us a xxs1500
and invited us to go as far as we could. It is a computer arquitecture
subject, so we wanted to use some periferic under linux and
assembler(requiered) to promote GNU stuff with other students.

The other alternative was to use YAMON, but we like linux and look
around YOUR source code ;-)

> > Looking at the kernel source code, I found that I can get the physical
> > address subtracting 0x8000000, but It doesnt seem to work.
> Not always.  On systems like this one that are not cache coherent,
> we play games with mapped addresses to get uncached spaces
> or you need to apply various macros/functions to keep the space
> coherent.

We got the ac97 working, so we would make it much cooler if we get the
DMA working with the ac97. If there is no way, no problem.

So, If there is a way to get it I would appreciate it a lot. We use a
char device so I have to make an external program to pass the buffer.
Using this way, is there any easy way to solve the problem??

> > Any idea?
> Use a more simple example.  Maybe just update one of the
> LED displays on the board.
>         -- Dan

Thanks a lot! If there is no solution, dont worry,

Thanks again,


If anyone is interested, we are documenting what we are doing, but it
is in spanish :(

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