NoC Packet Switch - NoC Packet Switch - 1.1 English - PG313

NoC Packet Switches (NPSs) connect NMU and NSU interfaces in the NoC as shown in the following figure. The NPS features are as follows:

• Each NPS is a full-duplex 4x4 switch.
• Each port supports eight virtual channels in each direction.
• Each port is fully buffered and contains eight FIFOs (one per virtual channel).
• The switching system uses a credit-based flow control.
• A minimum of two latency cycles through the switch.
• Configurable QoS.
• Programmable routing table per input-port / per virtual channel:
  • The routing table is programmed through the NPI at boot-time.
  • The routing table can be re-programmed if the NoC is on hold (quiesced).

Figure 1. NoC Packet Switch

The switch receives incoming packets. The receiving switch sends flow control credits back to the transmitter switch. The flow control credits are the guarantee that the switch accepts the data transaction, and are therefore important for switch-to-switch communication.

When data arrives at a switch, it checks the destination ID in the packet header. It then determines the output port of the switch to route the packet to. The destination ID is checked to flag any fatal error conditions if a packet is mis-routed. A routing table uses the buffered destination address to select the required switch output port.

Output arbitration uses an incoming data transaction when the corresponding virtual channel buffer is empty. Otherwise the data is stored in the virtual channel buffer for subsequent virtual channel arbitration. Each cycle arbitration candidate from each input port is presented at each output port of a switch.