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AR# 60135

AXI Interconnect - Why is the AXI Interconnect ID width 0? How is ID width calculated?


When using an AXI Interconnect and other AXI infrastructure modules such as the crossbar, data width converter, or protocol converter, I notice that the AWID/WID/BID/ARID/RID signal widths change, sometimes disappearing completely.

Why does this occur?


The ID widths of AXI transactions can be changed by the AXI Interconnect, usually for protocol conversion or area savings.

As additional AXI Masters (slave interfaces on the Interconnect/Crossbar) are added in crossbar Maximum Performance SAMD mode, additional ID bits are added in order to route potentially reordered responses back to the proper master.

The following configurations will lead to the single-threaded operation, resulting in removed ID from the AXI infrastructure IP:
  • AXI4-Lite Configurations: AXI4-Lite does not support multiple threads, and thus no ID signals are provided.
  • Protocol Conversion: Conversion to AXI3 can potentially split IDs.
  • Crossbar SASD: Configuring the AXI Interconnect to be in Minimize Area mode will enforce ordering to reduce area.

When necessary in these modes, incoming ID values may be internally stored by the core to satisfy protocol ID reflection.

AR# 60135
Date 04/28/2014
Status Active
Type General Article
  • AXI Interconnect
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