cgminer README:
Advanced USB options:
The --usb option can restrict how many Avalon, BFL ASIC, BitForce FPGAs,
Klondike ASIC, ModMiner FPGAs or Icarus bitstream FPGAs it finds:
--usb 1:2,1:3,1:4,1:*
or
--usb BAS:1,BFL:1,MMQ:0,ICA:0,KLN:0
or
--usb :10
You can only use one of the above 3
The first version
--usb 1:2,1:3,1:4,1:*
allows you to select which devices to mine on with a list of USB
bus_number:device_address
All other USB devices will be ignored