Hi
According to Android user guide.pdf
Boot from SD card
Change the board boot switch to MMC2 (SD3) boot: (SW6) 01000010 (from 1-8 bit). To clear the bootargs env and set up
the booting from SD card in SD slot 3, you can use the following command:
U-Boot > setenv fastboot_dev mmc2 [eMMC as fastboot deivce]
U-Boot > setenv bootcmd booti mmc2 [Load the boot.img from SD card]
U-Boot > setenv bootargs console=ttymxc0,115200 init=/init video=mxcfb0:dev=ldb,bpp=32
video=mxcfb1:off video=mxcfb2:off fbmem=10M fb0base=0x27b00000 vmalloc=400M
androidboot.console=ttymxc0 androidboot.hardware=freescale #[Optional]
U-Boot > saveenv #[Save the environments]