Receive AXI4-Stream Interface - 7.2 English

Unlike the transmit AXI4-Stream Control interface, the receive AXI4-Stream Status interface has only one format type (TAG/FLAG).

The receive interface has been designed to allow throttling on both the AXI4-Stream Status bus and the AXI4-Stream Data bus. After receiving the Ethernet data, the receive channel initiates transfer on the AXI4-Stream Status Interface before starting the transfer on AXI4-Stream Data Interface. The completion of the transfers on these interfaces depends on their throttling. See Figure 2 for a receive waveform diagram. This diagram shows what signals are required when connected to a core such as AXI_DMA. When connecting to a core such as AXI_FIFO_MM_S, a signal minimization can be made because the receive status bus information is not required.

In this case, the external core must actively drive the signals axi_str_rxs_aclk and axi_str_rxs_aresetn, axi_str_rxs_tready must be tied High, and all of the axi_str_rxs* inputs to the external core can be left open.

For the loopback of the receive AXI4-Stream to transmit AXI4-Stream to work, the receive AXI4-Stream Data bus is throttled by the transmit AXI4-Stream Data bus until the receive AXI4-Stream Status has been received by the transmit channel.

The receive AXI4-Stream Status frame always contains six 32-bit status words (words 0 to 5). The following figure and tables show the definitions of these words. Reserve fields do not have defined values. If the parameter C_RXCSUM is 0, the receive checksum offload function is not included in the build and receive AXI4-Stream Status word 4, bits 15-0 are always zero. If C_RXCSUM is 1, the raw checksum is calculated for every frame received and is placed in the receive AXI4-Stream Status word 4. For more information about using the receive raw checksum value, see Partial TCP/UDP Checksum Offload in Hardware .

Receive AXI4-Stream Status word 5, bits 15-0 always contains the number of bytes in length of the frame being sent across the receive AXI4-Stream Status interface.

The axi_str_rxd_strb(3:0) bus is used to indicate how many bytes in the last 32-bit word of the AXI4-Stream Data bus. A 1 is used to indicate valid bytes. For example, axi_str_rxd_strb(3:0) = “0001” indicates that only the first byte of the last word of the AXI4-Stream Data bus [axi_str_rxd_data(7:0) ] is valid and the remaining three bytes are unused. axi_str_rxd_strb(3:0) = “0011” would indicate that the first two bytes of the last word of the payload [axi_str_rxd_data(15:0)] are valid and the remaining two bytes are unused.