What is the relationship between sop, pvalid, hvalid and dvalid signal in RTile IP?

[myrfy001]

Regarding the specific behavior of the sop, eop, hvalid, and dvalid signals in the RTile, the design differs from the previous PTile interface. The single valid signal in the PTile interface has been split into hvalid and dvalid in the RTile. According to Section 4.3.1.1 in the "ug20316 R-Tile Avalon® Streaming Intel® FPGA IP for PCI Express* User Guide" (referred to as the manual):

This is defined to enable pipelined Header/Prefix and Data transfers to meet the bandwidth target. For example, while transferring the Data for one TLP, the Header and Prefix for the next TLP can also be transferred.

 The exact meaning of the sop signal is not explicitly explained in the manual, and there are even contradictory statements. Thus, there are two hypotheses:

A. sop marks the start of a new TLP, meaning sop and hvalid always occur simultaneously.

B. sop marks the start of the data portion within a TLP, meaning sop and the first dvalid signal of a TLP always occur together.

Conflicting Points:

• In Table 56 of the manual, sop is described in relation to pX_rx_stN_eop_o and rx_stN_valid_o, but it's unclear whether rx_stN_valid_o refers to hvalid or dvalid. However, the example given ("For example, when asserted, rx_st2_sop_o signals the start of a TLP on rx_st2_data_o[255:0]") implies that sop is associated with dvalid, supporting Hypothesis B. This also suggests that if a TLP doesn't contain a payload, there would be no sop signal but an eop signal.
• In Table 58, sop is said to be asserted for one clock cycle per TLP and qualifies the corresponding tx_stN_hdr_i and tx_stN_tlp_prfx_i signals. This description indicates that sop should be high simultaneously with hvalid to ensure correct transmission of the TLP header, supporting Hypothesis A.
• If both Hypotheses A and B are true, the only scenario is that if sop, hvalid, and dvalid signals appear for a TLP, they must do so synchronously. This contradicts the description in Section 4.3.1.1, which allows the header to be transferred ahead of the data.

In summary, the manual's descriptions create ambiguity regarding the sop signal's behavior. Clarification from the manual's context or additional information is needed.