Completion Data Ordering

AXI specifications mandate that if there are outstanding read requests with same MASTER_AXI_ARID, read data should be returned by the AXI slave interface in order. However, because each of these outstanding read requests are assigned unique tags on the PCIe side, the PCIe ordering rules permit the read completions to come back in any order. The PCIe Controller re-orders the out-of-order completions and issues them out on the AXI slave read data channel in the correct order. If the client issues read requests with unique MASTER_AXI_ARID, the AXI ordering rules permit the read data to come back out of order and the PCIe Controller issues the read data in the order it comes back from the PCIe link.