Loads the firmware-filename into the currently selected firmware location. See VM/CCUSB Firmware loaders for the full load procedure.
If serial-string is provided it must be a serial number string for a powered up device attached to the system. The VM-USB with that serial number will be used.
The format of firmware files does not match the documentation available. For .bit files it is necessary to skip headers to get to the load data. If you have bit files that are not loadable report this problem and use the corresponding .bin file instead.