Transfer of Completions with No Data - 3.4 English

Versal Adaptive SoC CPM Mode for PCI Express Product Guide (PG346)

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3.4 English

The following figure illustrates the transfer of a Completion TLP received from the link with no associated payload across the requester completion interface. The timing diagrams in this section assume that the Completions are not straddled on the interface. The straddle feature is described in Straddle Option for RC Interface.

Figure 1. Transfer of a Completion with No Data on the Requester Completion Interface

The entire transfer of the Completion TLP takes only a single beat on the interface. The core keeps the signal m_axis_rc_tvalid asserted over the duration of the packet. The user logic can prolong a beat at any time by pulling down m_axis_rc_tready. The AXI4-Stream interface signals m_axis_rc_tkeep (one per Dword position) indicate the valid descriptor Dwords in the packet. That is, the m_axis_rc_tkeep bits are set to 1 contiguously from the first Dword of the descriptor until its last Dword. The signal m_axis_rc_tlast is always asserted, indicating that the packet ends in its current beat.

The m_axi_rc_tuser bus also includes a signal is_sop[0], which is asserted in the first beat of every packet. The user logic are optionally use this signal to qualify the start of the descriptor on the interface. When the straddle option is not in use, none of the other sop and eop indications within m_axi_rc_tuser are relevant to the transfer of Completions.