Each NMU, NPS, and NSU source needs to have credit before it can send data to the receiver. After a reset, every NoC component has its source-credit reset to zero. The source unit connects to the destination unit using a bi-directional ready signal that indicates credit exchange is ready. Components wait until both directions are ready before starting the credit exchange.
The destination unit can send up to one credit per cycle, per virtual channel, to the source unit. The source unit can send up to one data transaction per cycle to the destination unit.