How to use USB mass storage in U-Boot

This page explains how to use the U-Boot command "ums" to update an SD card or eMMC on the device.

1. ums command[edit source]

In U-Boot, you can directly export the available block devices (sd/mmc/usb) as USB mass storage devices with ums command:

  help ums
 ums - Use the UMS [USB Mass Storage]
 
 Usage:
 ums <USB_controller> [<devtype>] <dev[:part]>  e.g. ums 0 mmc 0
     devtype defaults to mmc

This U-Boot command "ums" is infinite (a loop in USB treatments), and the U-Boot console is blocked until user enters a Ctrl-C.

2. Exporting a block device[edit source]

On ST boards, the OTG USB controller device index is 0, SD card = "mmc 0" and, when available, eMMC = "mmc 1".
You can check the device connected on an SDMMC with the U-Boot command "mmc info".

You can also export a USB device connected to the USB host controller (USBH) = "usb 0".

Then execute one of the following commands:

                                Comments
  ums 0 mmc 0 --> start ums on SD card
 Ctrl-C

                                Comments
  ums 0 mmc 1 --> start ums on eMMC
 Ctrl-C

                                Comments
  usb start   --> start USB host controller
  ums 0 usb 0 --> start ums on USB device 0 (USB key for example)
 Ctrl-C
  usb stop    --> stop USB host controller

After a delay (of up to 15 seconds), the host sees the exported block device and you can use any command on the PC to access the partitions of the exported memory (dd, mount, cp, rsync). A Ctrl-C is needed to stop the command.