Back-Pressure - 2022.2 English

Vitis Networking P4 User Guide (UG1308)

Document ID
UG1308
Version
2022.2 English
Revision

Vitis Networking P4 could issue back-pressure on the S_AXIS interface by bringing the TREADY signal Low. This can happen in the following scenarios:

  • TREADY is Low at the M_AXIS interface.
  • Back-pressure is generated within the Deparser because of header insertions extending a packet's length.
  • Back-pressure is generated by the CAMs if they are using TDM and if the specified Packet Rate is exceeded and causing excessive table lookup requests (refer to the description of the Packet Rate field in Chapter 3, Vitis Networking P4 Tool Flows).
  • Back-pressure is generated for a few clock cycles post s_axis_aresetn.

When there are CAMs present in the design, it takes a few clock cycles to stop back-pressure after it has been applied. If CAMs are not present, back-pressure will stop instantly.