Reference the "AM335x Sitara Processors Technical Reference Manual", Page 4392.
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• MMC0 supports booting from the MMC/SD card cage and also supports booting from
eMMC/eSD/managed NAND memory devices with less than 4GB capacity.
• MMC1 supports booting from eMMC/eSD/managed NAND memory device with 4GB capacity or
greater.
The restriction is a result of many eMMC devices not being compliant with the eMMC v4.41 specification.
If you have the need to boot from two different card cages, many MMC/SD cards will boot from MMC1, but
for maximum compatibility only MMC0 should be used to boot from the card cage. Similarly for maximum compatibility, booting from eMMC/eSD/managed NAND should only be performed on MMC1.
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