We are developing custom board with i.MXRT1051 uC. It is supposed to boot from eMMC (but it fails). At this point it's set to boot in internal boot mode (ROM bootloader) with GPIO BOOT_CFG disabled (BT_FUE_SEL=1) & BOOT_CFG1(7:6)=0x10 (MMC/eMMC boot). Rest of fuses is untouched. What fuses shall be set to boot in such mode ? eMMC is Kingston EMM04G-M627-x02U and supports:
Legacy MMC: SDR; 3,3/1,8V; 1,4,8-bit
High Speed SDR: SDR; 3,3/1,8V; 4,8-bit
High Speed DDR: DDR; 3,3/1,8V; 4,8-bit
HS200: SDR; 1,8V; 4,8-bit
HS400: DDR; 1,8V; 8-bit
What I understand from i.MXRT1050 RM it shall boot in 4-bit SDR mode with BOOT_CFG2(2:1)=00.
Is it possible that uC doesn't support particular eMMC boot mode even if it's mentioned in RM ?
How to debug ROM bootloader to find out what's wrong ?