GSOC 2015: Raspberry Pi Low Level Peripherals and SD Card

[Joel Sherrill]

On 03/25/2015 05:41 PM, André Marques wrote:
> On 25-03-2015 14:17, Gedare Bloom wrote:
>> On Wed, Mar 25, 2015 at 4:49 AM, André Marques
>> <andre.lousa.marques at gmail.com>  wrote:
>>> Hello everyone,
>>>
>>> My GSoC proposal entitled "Raspberry Pi Low Level Peripherals and SD Card"
>>> can be found for review at:
>>>
>>> https://docs.google.com/document/d/11K0qU3OsbSMhNYkTTWt4kitAbd6uuJBcMfA_07Lg6j8
>>>
>>> One issue I would like to discuss here is related to the SD card support,
>>> which as exposed on the proposal the GPIOs to which the SD card is connected
>>> internally do not have SPI hardware capabilities, meaning that to access the
>>> card via SPI mode it would have to be bit-banged on those GPIOs (a problem
>>> on performance). This is more detailed on the proposal, but another
>>> alternative would be to use the SD mode instead, with the help of the PI's
>>> EMMC module, and the SD simplified specifications as documentation for the
>>> SD protocol. I have already used this setup with success in the past, and it
>>> should have better performance. In this setup the FreeBSD SD/MMC stack may
>>> be used (such as the one Sebastian Huber ported last year ->
>>> https://git.rtems.org/sebh/rtems-libusb.git/tree/rtems/freebsd/dev/mmc?id=3c82a1500da3192de2504a1360e065fd84a1f3a0)
>> Is this code in the libbsd.git now?
> It is not, only on Sebastian's repository. It was anounced here along
> with an USB host stack:
>
> https://lists.rtems.org/pipermail/devel/2014-August/007873.html
>
Hmm.. the libbsd code was updated to FreeBSD 9.x as a base.
Maybe he merged this code at that point.

>>> which implements the SD protocol also based on the simplified specs. This
>>> would help avoiding implementing the protocol from scratch (which is sort of
>>> what I did in my previous effort with the SD card and the PI) and would be
>>> better for maintenance probably.
>>>
>>> My issue is then on the feasibily (licence wise) of having the FreeBSD SD
>>> stack or having code based on the SD Simplified Specs on the RTEMS tree.
>>>
>> FreeBSD code should be fine. The complexity of getting libbsd working
>> could be the real stumbling block. But I think others will be working
>> on the same problem too, so there may be some ability to share
>> knowledge.
>>
>>> In SPI mode an implementation of the protocol can be found in
>>> libchip/i2c/spi-sd-card.*, which could in that case be used/improved further
>>> during the project, if it is decided it is best to use SPI mode. This uses
>>> the libi2c API, which is deprecated for I2C but, as I understand, still
>>> stands as the API for SPI (information about that would also be
>>> appreciated).
>>>
>> It's just the no one has replaced it yet! There seem to be multiple
>> efforts going on now to get more driver-like frameworks into RTEMS.
> If any actual effort is currently going or planned for a new SPI API it
> would be interesting to know so it can be taken into account, so it does
> not come as a surprise mid-GSoC.
>
>>> Thanks,
>>> André Marques.
>>> _______________________________________________
>>> devel mailing list
>>> devel at rtems.org
>>> http://lists.rtems.org/mailman/listinfo/devel
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