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
In U-Boot, you can directly export the available block devices (sd/mmc/usb) as USB mass storage devices with ums command:
Board $> 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
You can also export a USB device connected to the USB host controller (USBH) = "usb 0".
Then execute one of the following commands:
Comments Board $> ums 0 mmc 0 --> start ums on SD card Ctrl-C
Comments Board $> ums 0 mmc 1 --> start ums on eMMC Ctrl-C
Comments Board $> usb start --> start USB host controller Board $> ums 0 usb 0 --> start ums on USB device 0 (USB key for example) Ctrl-C Board $> 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.
See also How to update U-Boot on an SD card.
former spelling for e•MMC ('e' in italic)
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