ums <dev> [<interface>] <devnum[:partnum]>
Use the USB Mass Storage class (also known as UMS) to make accessible an U-Boot block device (fully or with U-Boot’s partition syntax) to a USB host and to enable file transfers. U-Boot, the USB device, acts as a simple external hard drive plugged on the host USB port.
This command “ums” stays in the USB’s treatment loop until user enters Ctrl-C.
USB gadget device number
interface for accessing the block device (mmc, sata, scsi, usb, ….) defaults is “mmc”
device number for selected interface
partition number or 0 to expose all partitions, defaults to 0
=> ums 0 mmc 0 => ums 0 usb 1:2
The ums command is only available if CONFIG_CMD_USB_MASS_STORAGE=y and depends on CONFIG_USB_USB_GADGET and CONFIG_BLK.
The return value $? is set to 0 (true) when the USB stack was successfully started and interrupted, with Ctrl-C or after USB cable issue (detection timeout or cable removal).
If an error occurs, the return value $? is set to 1 (false).