You can do this easily by referencing `/dev/disk/by-id/usb-manufacturername_*serialnumber*`. These appear as symbolic links which you can dereference using `readlink -e` to determine the associated block device. These links are however created by `udev` which might not be present in your embedded environment.

Or.. Look at the `dmesg` after connecting the USB device. It should give you the `/dev` node.