Flex Interface Timestamping - 1.3 English

Versal Devices Integrated 100G Multirate Ethernet MAC Subsystem Product Guide (PG314)

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1.3 English

The 1588 timestamping is available when the MRMAC is in the flexible interface mode. Only 2-step timestamping is available and 1-step timestamping (insertion) is not supported. To enable the feature and associated ports, set the control bit ctl_pcs_ts_en to 1.

Note: In both RX and TX Flex I/F timestamping, Clause 49/82 conversion causes inaccurate timestamps. If conversion is required with 1588, it should be done external to the MRMAC. Also, timestamping is not supported in FEC only or FC32 modes.

The RX Flex I/F timestamps use the same output port as the normal ingress timestamps (rx_ptp_tstamp_out_<N>). Enabling Flex I/F timestamps switches these ports over to the flexif clock. As decoding is not performed on the packet, the timestamp corresponds to the first word on the datapath and not the first word of the frame. For high accuracy, user logic can add block offsets to the timestamp value if the start of packet is not on the first word of the datapath.

In the egress direction, the Flex I/F timestamping feature uses a different set of signals to request a timestamp and provide a tag (tx_ptp_flex_*_<N>). However, the usual egress timestamp interface is used to produce the results.

Note: The egress timestamp output uses the AXI4-Stream clock regardless of the chosen timestamp mode.

An additional signal is present on the Flex I/F in the egress direction: tx_ptp_flex_1588loc_in_<N>[1:0]. In the egress direction, the user logic is required to explicitly identify the lane containing the start of the packet (that is, the lane in which data following SFD is present) by asserting Bit[0] of the per-lane (<N>) signal. If the Flex I/F is in Clause 74 (KR-FEC) mode, Bit[1] of the relevant signal should be set to 1 if the start is offset by 32 bits (if the Flex I/F is in Clause 74 KR-FEC) mode. In this method, the TX timestamp accurately reflects the position of the start of packet.