04-29-2020, 12:54 PM
The PBP uses (a modified, I believe) Das U-Boot. The SoC doesn't require anything to boot from SD, but it's last in the boot order. One of the modifications to U-Boot for the PBP is placing the SD before the eMMC in boot priority. There are a few images using an older mainline U-Boot, that does not prioritize the SD. However, most don't use that U-Boot version, and will boot an image from SD so long as you insert it before booting. No changes to conf files necessary.
I believe the only way currently to enable and view to the U-Boot menu would be through UART. (Be sure to search the forums and read carefully on this, as the UART cable in the store will cause problems with the PBP. You'll need a cable that's 3.3v not 5v.)
IIRC, video drivers would have to be added to U-Boot to see the boot menu. It might be worth waiting for cyrstalgamma's levinboot (a replacement bootloader.)
I believe the only way currently to enable and view to the U-Boot menu would be through UART. (Be sure to search the forums and read carefully on this, as the UART cable in the store will cause problems with the PBP. You'll need a cable that's 3.3v not 5v.)
IIRC, video drivers would have to be added to U-Boot to see the boot menu. It might be worth waiting for cyrstalgamma's levinboot (a replacement bootloader.)