Re: [Gumstix-users] Working DMA example?

[Dave H. <dhy...@gm...>]

Hi Mark,

On 7/18/06, Heilpern, Mark <mar...@au...> wrote:
> Does anyone have an example of working DMA code for the PXA255 / Linux?
> I've been trying to get this working but every time I start the DMA I
> receive a bus error; I'm sure I'm not getting a valid physical address
> in somewhere but I'm not sure how to fix it.
>
> I'm trying to set the NSSP (FIFO located at physical 0x41400010) as the
> data source, and RAM as the target. I'm trying to set this up using DMA
> descriptors. Relevant snippets of DMA-related code I'm using are below.
> Thanks for any advice!

Hmmm. You can find DMA samples for SPI in drivers/spi/pxa2xx_spi.c

You'd be better off to use the infratructure that's already present
since it supports DMA to/from the NSSP channel.

The USB driver also supports DMA.

Personally, I wouldn't build the descriptors myself. DMA memory is
tricky because it has to also be uncached.

There are a bunch of routines in the kernel for dealing with DMA
(you'll see them in the sample mentioned above).

I also see some documentation in Documentation/DMA-mapping.txt

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/