Hi, I have studied the booting sequence and boot modes of the OMAP5.
Basically we can simply use the standard order (0x1010) as set on the eval board:
1. SD 2. eMMC 3. USB
So I think there is no need for a trick as on the Beagle Board to press some AUX button to modify the boot order to get SD first if X-Loader in NAND is damaged.
What we *could* do is to add a 32 byte eeprom to I2C1 and then we can define the boot order ourselves. E.g. SD -> eMMC (boot partition) -> eMMC -> SATA -> UART3 -> USB
But I think this is overkill.
So my proposal is to have it simply as in the EVM: boot from SD (only one slot is boot capable!) and if no SD, boot from eMMC.
This means people can either have their full bootable system on SD. They can still boot from eMMC if they don't insert the SD. Or they always boot from eMMC because they use non-bootable SD card.
Unbricking is simply by booting from any bootable SD and restoring eMMC.
I think TI was able to change that from OMAP3 booting because the SD slot on the OMAP5 has an explicit card detect input. So the boot sequence is not slower if the SD card is not present but in the first position. This was probably the reason to boot from NAND by default and the need for the AUX button trick.
BTW: it appears that it is not possible to switch the sys_boot pins to GPIO mode and therefore read some AUX button.
BR, Nikolaus