Raspberry Pi SD card support

[Joel Sherrill]

On 4/4/2014 1:15 PM, Gedare Bloom wrote:
> The license looked fine to me.
+1

As always, we just need to be careful on a file per file basis just in case
something else in rpi-boot has a different license.
> On Thu, Apr 3, 2014 at 10:06 PM, Alan Cudmore <alan.cudmore at gmail.com> wrote:
>> From my limited research, it looks like the emmc controller in the Raspberry
>> Pi BCM2835 may be the way to go.
>> It looks like it is a high level controller for the SD/MMC card slot on the
>> Pi.
>>
>> Since this is a custom controller, I don't think there would be an existing
>> driver in RTEMS.
>>
>> It seems that this emmc controller in the Pi may handle different types of
>> cards, and at a higher level than just using the SPI bus to access the card.
>> ( This is based on some searches of conversations on the raspberry pi forums
>> , not my experience )
>>
>> You would have to write a driver for this emmc controller and provide the
>> interface to libblock for the file system interface on RTEMS. The code you
>> have linked above for rpi-boot looks like it has a permissive license, so it
>> *may* be possible to use this code in the RTEMS driver. There is some other
>> potentially useful code in there too.
>>
>> I'll have to try the serial bootloader, I am also close to ordering an
>> inexpensive JTAG adapter to try loading and debugging through JTAG. uboot is
>> another possibility, using a TFTP server.
>>
>> Alan
>>
>>
>>
>>
>> On Wed, Apr 2, 2014 at 12:02 PM, Andre Marques
>> <andre.lousa.marques at gmail.com> wrote:
>>> Hello,
>>>
>>> I'm intending to work in the SD card support for the Raspberry Pi BSP,
>>> using the SD mode instead of the SPI mode.
>>>
>>> The references I have gathered so far for this are as follows:
>>>
>>> The Raspberry Pi SOC guide: Broadcom BCM2835 Peripherals Guide (Chapter 5
>>> - EMMC)
>>>
>>> The simplified SD standard -
>>> https://www.sdcard.org/downloads/pls/simplified_specs/
>>>
>>> And the following github code -
>>> https://github.com/jncronin/rpi-boot/blob/master/emmc.c
>>>
>>> There is also the libchip/i2c/spi-sd-card libi2c driver, which can also be
>>> a reference (even though it uses SPI).
>>>
>>> Now, the questions:
>>>
>>> Should I use the Generic Disk Device driver, as the
>>> libchip/i2c/spi-sd-card ?
>>>
>>> Is there any driver using the SD mode for sd card access, or using an emmc
>>> interface currently in the RTEMS code base? I haven't found any.
>>>
>>> On a side note, I managed to send RTEMS applications to the RPi though the
>>> UART interface using the xmodem protocol.
>>>
>>> For that I used the following bootloader
>>>
>>> https://github.com/dwelch67/raspberrypi/tree/master/bootloader05
>>>
>>> It takes me 2 minutes to send 1 MB of data to the RPi, but this could be
>>> improved if it used 1024 byte block transfer instead of the default of 128.
>>> The bootloader loads the transfered program to memory and runs it. Then the
>>> RPi must be rebooted so a new program can be sent.
>>>
>>> It may not be the best way, but only requires an usb-to-uart cable, and
>>> avoids the current SD card "dance" to run programs on the Pi.
>>>
>>> Thank you for your time.
>>>
>>> --André Marques
>>>
>>>
>>
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>>
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-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
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