On 6/6/2013 8:59 AM, Gerald Coley wrote:
> You can force a boot by removing the MLO from the eMMC card, erasing it, or
> holding the Boot button down. However, shorting the Boot button also shorts
> the LCD pin causing the HDMI image to be affected. If you do not want he
> UBoot to enable the eMMC, then simply change the code to enable eMMC,
> activate the RESET pin, and activate the reset pin and then move on.
I've now crawled through the docs, and it looks like holding the boot
button down at power-on will work for the BeBoPr board, but this doesn't
fully replicate the 'White behavior as now the SPI0 pins are twiddled by
the ROM code which the 'White doesn't do. It's also not likely users
will remember to hold the button down every time they boot.
Since the BeBoPr board doesn't use any of the SPI pins, it would be
enough to swap one resistor (move R68 to R93) which will make the board
behave like the boot button is always pressed (but not short the
LCD_DATA2 line to ground). This would work for any capes that don't
mind the SPI0 lines twiddling while the ROM code tries to boot before it
falls back to the SD card (MMC0).
To fully mimic the 'White is a bit more complex:
Move R67 to R92 (SYS_BOOT3 = 0)
Leave R68 alone (SYS_BOOT2 = 1)
Move R94 to R69 (SYS_BOOT1 = 1)
Move R95 to R70 (SYS_BOOT0 = 1)
This will boot from the SD card slot first, without trying to boot from
any other source (the same boot mode used on the BeagleBone white), but
software somewhere will need to insure the eMMC reset line for the
'Black is asserted before anything tries to talk to the pins connected
to the eMMC interface.