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.marq...@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.
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