Non-Posted Transactions with a Payload - 3.4 English

Versal Adaptive SoC CPM Mode for PCI Express Product Guide (PG346)

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3.4 English

The transfer of a Non-Posted request with a payload (an I/O write request, Configuration write request, or Atomic Operation request) is similar to the transfer of a memory write 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 128-bit address aligned mode, the payload must start in the second 128-bit quarter of the first beat, following the descriptor. The payload are start at any of four Dword positions in this quarter. The offset of its first Dword must be specified in the field addr_offset[15:0] of the s_axis_rq_tuser bus.

In the case of I/O and Configuration write requests, the valid bytes in the one-Dword payload must be indicated using first_be[15:0]. For Atomic Operation requests, all bytes in the first and last Dwords are assumed valid.