3.5. Config Slave (CS)
This interface is applicable only in Root Port mode. The Config Slave (CS) is an AVMM non-bursting interface and essentially converts single-cycle, Avalon-MM read and write transactions into AVST reads and writes for the PCIe configuration TLPs to be sent to PCIe Hard IP (to be sent over the PCIe link). This module also processes the completion TLPs (Cpl and CplD) it receives in return.
CS module converts the AVMM request into a configuration TLP with a fixed TAG value (decimal 255) assigned to it and sends it to scheduler. One unique TAG is enough as it doesn’t support more than one outstanding transaction. This unique TAG helps in rerouting the completions to CS module.
Re-routing the completion is handled at the top level and since only 1 NP outstanding is needed, the TLP RX scheduler parses the completion field to decode the completion on a fixed TAG and route the transaction over to CS.