On the RQ interface, the user application delivers each TLP as an AXI4-Stream packet. The packet starts with a 128-bit descriptor, followed by data in the case of TLPs with a payload. The following figure shows the signals associated with the requester request interface.
The RQ interface supports two distinct data alignment modes for transferring
payloads. In the Dword-aligned mode, the user logic must provide the first Dword of the
payload immediately after the last Dword of the descriptor. It must also set the bits in
first_be[3:0] to indicate the valid bytes in the
first Dword and the bits in last_be[3:0] (both part of
the bus s_axis_rq_tuser) to indicate the valid bytes in
the last Dword of the payload. In the address-aligned mode, the user application must
start the payload transfer in the beat following the last Dword of the descriptor, and
its first Dword can be in any of the possible Dword positions on the datapath. The user
application communicates the offset of the first Dword on the datapath using the addr_offset[2:0] signals in s_axis_rq_tuser. As in the case of the Dword-aligned mode, the user
application must also set the bits in first_be[3:0] to indicate the
valid bytes in the first Dword and the bits in last_be[3:0] to indicate the valid bytes in the last Dword of the
payload.