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?
> 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. > Thanks, > André Marques. > _______________________________________________ > devel mailing list > devel@rtems.org > http://lists.rtems.org/mailman/listinfo/devel _______________________________________________ devel mailing list devel@rtems.org http://lists.rtems.org/mailman/listinfo/devel
