Re: PXA270 SPI + SD card

[Ned Forrester <nforrester-/d+BM93fTQY@public.gmane.org>]

On 11/04/2009 04:54 PM, Cliff Brake wrote:
> On Wed, Nov 4, 2009 at 4:53 PM, Cliff Brake <cliff.brake-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> Hello,
>>
>> I'm trying to get a PXA270 to talk to a SD card via SPI.  Has anyone
>> else done this?

I haven't used an SD card, but...

>> One of the requirements is the CS stay low for the entire transaction.
>>  Can this be done with the PXA270 controlling the frame (CS) signal,
>> or is GPIO control typically required?

A GPIO is typically used.  The PXA2xx processors lack a
multi-chip-select function for SPI devices, so one has to use a GPIO if
more than one device is on the bus.  Back in 2.6.20, there was a
cs_control() call back to allow the pxa2xx_spi.c driver to control a
separately allocated GPIO line.  I think there is now a more generalized
procedure in the kernel to specify the GPIO that is to be used for each
device on the bus.

> Also, what SPI mode is typically used for SD?  Looks like 0 and 3 are
> the closest (http://elm-chan.org/docs/spi_e.html).

Not sure on that one.  I think there was a lot of discussion about that
a couple of years ago when someone was getting SD cards to work.  You
might want to search the archives if no one answers you directly.

-- 
Ned Forrester                                       nforrester-/d+BM93fTQY@public.gmane.org
Oceanographic Systems Lab                                  508-289-2226
Applied Ocean Physics and Engineering Dept.
Woods Hole Oceanographic Institution          Woods Hole, MA 02543, USA
http://www.whoi.edu/
http://www.whoi.edu/sbl/liteSite.do?litesiteid=7212
http://www.whoi.edu/hpb/Site.do?id=1532
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