The transfer of a Non-Posted request with payload (an I/O write request, Configuration write request, or Atomic Operation request) is similar to the transfer of a memory request, with the following changes in how the payload is aligned on the datapath:
• In the Dword-aligned mode, the first Dword of the payload follows the last Dword of the descriptor, with no gaps between them.
• In the address-aligned mode, the payload must start in the beat following the last Dword of the descriptor. The payload can start at any Dword position on the datapath. The offset of its first Dword must be specified using the addr_offset[2:0] signal.
For I/O and Configuration write requests, the valid bytes in the one-Dword payload must be indicated using first_be[3:0] . For Atomic Operation requests, all bytes in the first and last Dwords are assumed valid.