[U-Boot] uboot read usb usb mass storage device

Board:AT91SAM9G20 OS:Linux Soft Version:uboot 1.3.4 In u-boot/include/configs/at91sam9g20ek.h ,it had add #define CONFIG_CMD_USB and #define CONFIG_CMD_FAT but I use "usb start"cmd when my board run in uboot,it can not scan the usb storage,and print ERROR:CTL TIMEOUT how to solute.