Ordering Between Posted and Non-Posted Writes
The PCIe Controller ensures strict ordering between posted and non-posted
writes on the AXI master write interface. All posted write requests are issued with the same
TARGET_AXI_AWID so that they complete in order in the AXI subsystem.
When a non-posted write follows a posted write, the PCIe Controller ensures
that all outstanding posted writes complete (i.e., TARGET_AXI_BVALID is
received for all outstanding write transactions) before issuing the non-posted write. This
process ensures that non-posted transactions are not processed before posted transactions.