Raspberry Pi SD card support

[Andre Marques]

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