Operational Rules - 3.1 English - PG369

Segment Ordering

The 128-bit segments are ordered 0 to N; the first of the 128-bit transfers occurs on segment 0, the second on segment 1, and so forth. During each clock cycle that data is valid (tvalid asserted), an idle cycle (no data) is indicated with inactive segment 0 (tuser_ena0 == 0). If the cycle is not a full IDLE and some data is present, segment 0 must be active (tuser_ena0 == 1). The segmented bus is aligned such that the first byte of data is placed in bits 7:0 of segment 0.

Active Segments

Data is transferred in a segment on the interface when the corresponding tuser_ena bit is asserted. Segments must be filled in sequence with no gaps between active segments.

Gaps Subsequent to EOP

Segments must be filled in sequence with no gaps between active segments. However, if a segment has an eop, the subsequent segments might be inactive. Furthermore, if the segment after the eop is inactive, all subsequent segments in that cycle must be inactive.

Channel Correlation

Because the DCMAC Subsystem implements pre-indication of channel using the id_req_vld and id_req signals, there must be a guaranteed correlation between those indicated signals and the response tvalid and tid pair wherein the two signal sets are identical but tvalid and tid are time shifted by a fixed and static number of clocks.

The DCMAC Subsystem guarantees correlation between valid tid signals presented by the transmit AXI4-Stream client and valid ch_status_id signals presented on the ch_status interface. In this case, however, it is not an exact mirroring because ch_status_vld is only asserted when ch_status_skip_req is asserted. Regardless, it is guaranteed that the DCMAC Subsystem will not provide channel status information any more frequently than the channel’s tid is presented by the AXI4-Stream client.

Preambles

The DCMAC Subsystem's channelized AXI4-Stream bus can support up to three sop signals per cycle; the corresponding preambles are provided on tx_axis_preamblein_{0,2,4}. The tx_axis_preamblein_0 is used for sop signals in segments 0–3, tx_axis_preamblein_2 is used for sop signals in segments 4–7, and tx_axis_preamblein_4 is used for sop signals in segments 8–11.