Altera® AXI4 Bus Functional Model User Guides

ID 838773
Date 5/19/2025
Public
Document Table of Contents

2.2.2. AXI4 Streaming Data Transfer

Data transfers occur on the AXI4 streaming bus by use of the TVALID and TREADY handshaking signals between the transmitter and receiver.

TVALID, driven by the transmitter, lets the receiver know that data is ready to send. TREADY, driven by the receiver, lets the transmitter know that the receiver is ready to receive the data from the transmitter.

For a transfer of data to occur, both TVALID and TREADY must assert during a clock cycle on the bus. Each clock cycle on the bus is a beat. There may be only one beat required to conclude a transfer, or there may be many beats required to conclude a transfer, depending on the amount of data the transmitter sends in a single transfer. The transmitter indicates the end of a transfer with the TLAST signal. The beat of data provided during TLAST is the last beat of the current transfer. The next time that TVALID asserts, this indicates the beginning of the next transfer.

AXI4 Streaming Single Beat Data Transfer with TVALID Asserted before TREADY shows a simple single-beat transfer handshake with TVALID asserted before TREADY.

Figure 9. AXI4 Streaming Single Beat Data Transfer with TVALID Asserted before TREADY
Note: The transmitter is not permitted to wait until TREADY is asserted before asserting TVALID. Once TVALID is asserted, it must remain asserted until the handshake occurs. The receiver is permitted to wait for TVALID to be asserted before asserting TREADY. The receiver is permitted to assert and deassert TREADY without TVALID being asserted.6

AXI4 Streaming Single Beat Data Transfer with TREADY Asserted before TVALID shows how TREADY is asserted before TVALID during a single beat transfer.

Figure 10. AXI4 Streaming Single Beat Data Transfer with TREADY Asserted before TVALID

Neither transmitters nor receivers need to wait for each other to initiate a data transfer. AXI4 Streaming Single Beat Data Transfer with TREADY and TVALID Asserted Simultaneously shows that TVALID and TREADY are asserted simultaneously to create a single-beat transfer.

Figure 11. AXI4 Streaming Single Beat Data Transfer with TREADY and TVALID Asserted Simultaneously
6 From Section 2.2, AMBA AXI-Stream Protocol Specification, ARM IHI 0051B ID040921