The transfer of an I/O read request on the CQ interface is similar to that of a
memory read request, and involves only the descriptor. The length of the requested data
is always one Dword, and the First Byte Enable bits on m_axis_cq_tuser
indicate the valid bytes to be read.
The user logic must respond to an I/O read request with a one-Dword Completion (or a Completion with no data in the case of an error). Completions for two distinct I/O read requests can be sent in any order. The integrated block signals errors associated with an I/O read transaction by setting the Completion Status field in the completion descriptor to CA (Completer Abort) or UR (Unsupported Request), as appropriate. The operation of the Completer Completion interface is described in Completer Completion Interface Operation.