S2MM Descriptor Settings and AXI Status Stream - 7.1 English

The relationship between descriptor RXSOF/RXEOF settings and the AXI Status Stream are illustrated in This Figure . The descriptor with RXSOF=1 describes the buffer containing the first part of the receive packet. The Descriptor with RXEOF=1 describes the buffer containing the last part of the receive packet.

For proper operation, the software must specify enough buffer space (the sum of the buffer lengths in each descriptor of the descriptor chain) to be greater than or equal to the maximum sized packet that is received.

Figure 2-38: Detail of Descriptor Relationship to S2MM Stream and Status Stream

X-Ref Target - Figure 2-38

If the Status/Control Stream is included, the status received is stored in the User Application fields (APP0 to APP4) of the descriptor with RXEOF set.

The actual byte count of received and stored data for a particular buffer is updated to the Transferred Bytes field in the associated descriptor. The software can determine how many bytes were received by walking the descriptors from RXSOF to RXEOF and adding the Bytes Transferred fields to get a total byte count. For applications where you provide the total length in the status stream, this value is stored in the user-defined application location in the descriptor with RXEOF=1.