Hardware：Beagleble white A6 Kernel：linux-3.2-2013.01.01-psp06.00.00.00 U-boot：u-boot-2013.01.01-psp06.00.00.00
AM335X支持从MMC0/1接口启动，但是有个很不爽的限制（AM335x Version K，注意！只有最新的K版本文档才有这个限制的描述， Section 26.1.7.5.2）：
26.1.7.5.2 System Interconnection
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.
手头上只有一个8G的eMMC卡，所以我试图从UART启动。 UART启动方式可参考文档：AM335x_U-Boot_Users_Guide.很多朋友问u-boot-spl.bin这个文件从哪里来，这个文件其实在uboot编译过程中就会产生，主要作用时spl初始化（板级基本初始化）。一个方法时可以find查找一下，二是可以看看uboot源码的Makefile就知道了，在编译文件目录的spl目录下面。
使用minicom上电，第一次用xmodem传输uboot-spl.bin,第二次传输uboot.img，稍等片刻即可进入uboot模式，然后扫描SD卡、eMMC、网络启动都不在话下了。