在 AM335X TRM的26.7.1.5.2 对 板子的 MMC 启动做了如下说明：
Each interface has booting restrictions on which type of memory it supports:
-• 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.
Note that the above restrictions only apply to booting from each port. Drivers can be written for either port
to support any desired interface.
Note:
• The ROM Code does not handle the card detection feature on card cage.
• If MMC1 is used the GPMC interface is not usable, due to pin muxing options.
• MMC1 supports sector mode without querying the card.
按照文档的说明，我的理解是： MMC0 不支持 boot from 等于或大于4G的 eMMC/eSD/managed NAND memory，
是因为这些 eMMC/eSD/managed NAND memory 不兼容 eMMC v4.41 specification的缘故；那么如果我们使用的是支持
eMMC 4.41 规范的 eMMC芯片，是否就可以没有这个限制了？
还有一个疑问是 文档上说的 MMC/SD card cage 和 eMMC/eSD/managed NAND memory 是两种不同类型的芯片？
我的理解是 eMMC芯片=NAND falsh+控制器+MMC的标准封装接口 ，它对应于文档上说的哪一种？
望各位大侠不吝赐教。
