GTS AXI Streaming Intel® FPGA IP for PCI Express* User Guide

ID 813754
Date 5/15/2024
Public

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6.3.1. AXI4-Stream Receive (RX) Interface

The packet received from the link is presented to application logic on this interface. The interface supports data width of 16 bytes (128 bits), 32 bytes (256 bits), and 64 bytes (512 bits). The TLP header, BAR, function number of TLP, and prefix signals are sent in line with data.

Table 36.   AXI4-Stream RX Interface
Signal Name Direction Clock Domain Description
p0_ss_app_st_rx_tvalid Output p0_axi_st_clk Indicates that the remote transmit interface is driving a valid transfer.
p0_app_ss_st_rx_tready Input p0_axi_st_clk Indicates that the receive interface can accept a transfer in the current cycle.
p0_ss_app_st_rx_tdata[(a-1):0] 1 Output p0_axi_st_clk

Data bus used to provide the data that is passing across the interface.

p0_ss_app_st_rx_tkeep[(a/8-1):0] 1 Output p0_axi_st_clk

A byte qualifier used to indicate whether the content of the associated byte is valid.

The invalid bytes are allowed only during ss_app_st_tx_tlast cycle.

The sparse ss_app_st_tx_tkeep is not allowed.

p0_ss_app_st_rx_tlast Output p0_axi_st_clk Indicates end of data/command transmission.
p0_app_ss_st_rx_tuser_halt[2:0] Input p0_axi_st_clk

Indicates that the user logic wants to temporarily halt reception of a particular type of packet.

  • bit[0]: Halt Posted TLP
  • bit[1]: Halt Non Posted TLP
  • bit[2]: Halt Completion TLP

The timing diagrams in the following sections are for the simple packing scheme.

The following figure shows a timing diagram for command with data. The completion, memory write, messages, and the configuration write commands fall under the command with data category.

The first command transfers a payload of 64 Bytes. The receive interface is ready to accept a command at clock cycle 1 but the transmit interface does not have any command to transfer in that same cycle. The transmit interface starts the transfer in the next cycle.

The second command transfers a payload of 128 Bytes. Here, the receive interface is not ready to accept a command when the transmit interface has asserted valid. The transmit interface holds the information on the bus until it observes ready from the receive interface.

Figure 41.  AXI4-Stream RX Interface—Simple Packing Scheme Timing Diagram (Command With Data)

The following figure shows a timing diagram for command with data followed by command without data. The completion, memory write, messages, and the configuration write commands fall under command with data category. The memory read, configuration read, messages without data, and completion without data fall under command without data category.

The first command transfers a payload of 64 Bytes. The receive interface is ready to accept a command at clock cycle 1 but the transmit interface does not have any command to transfer in that same cycle. The transmit interface starts the transfer in the next cycle.

The second command is a command without data. Here, the receive interface is not ready to accept a command when the transmit interface has asserted valid. The transmit interface holds the information on the bus until it observes ready from the receive interface.

Figure 42.  AXI4-Stream RX Interface—Simple Packing Scheme Timing Diagram (Command With Data Followed by Command Without Data)

The first command transfers the payload of 67 Bytes.

Note: tkeep during tlast has partial ones, but these ones are contiguous, sparse tkeep is not allowed. The partial tkeep is allowed only on tlast cycle.

The second command is a command without data.

Figure 43.  AXI4-Stream RX Interface—Simple Packing Scheme Timing Diagram (Back-to-Back Commands With Data and Without Data)
1 For the recommended a value, refer to the Variables Used in the Bus Indice table.