Human interface on SAM4S-EK:
- Led 0 (D2) is on when USB line is in IDLE mode, and off in SUSPEND mode
- Led 1 blinks when USB host has checked and enabled PHDC interface
- Led 2 is on when PHDC has validated association
- USRPB1 (BP2) and USRPB2 (BP3) are used to send a measure