The following figure shows the transfer of data in an AXI4-Stream channel. TVALID is driven by the source (master) side of the channel and TREADY is driven by the receiver (slave). TVALID indicates that the value in the payload fields (TDATA, TUSER, and TLAST) is valid. TREADY indicates that the slave is ready to receive data. When both TVALID and TREADY are asserted in a cycle, a transfer occurs. The master and slave set TVALID and TREADY respectively for the next transfer appropriately.
The DDS Compiler datapath channels (all except the CONFIG channel) can be configured to have no TREADY.
This is equivalent to setting TREADY for each of these channels permanently asserted. This inability to indicate backpressure simplifies the interface behavior and allows resource savings to be made. This mode is recommended when the system can be designed to ensure that full throughput (one sample per cycle) can be assured.
The AXI4 handshake shown in the preceding figure forbids the output of data until the downstream circuitry is ready. This allows for easy synchronization of circuits following power-up or reset without complicated latency calculations.
For more information on AXI4-Stream interfaces, see the AMBA AXI4-Stream Protocol Specification (ARM IHI 0051A).