Low Latency Ethernet 10G MAC Intel® FPGA IP User Guide

ID 683426
Date 3/01/2022
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4.10.2. TX Datapath

The IEEE 1588v2 feature supports 1-step and 2-step clock synchronizations on the TX datapath.

  • For 1-step clock synchronization,
    • Timestamp insertion depends on the PTP device and message type.
    • The MAC function inserts a timestamp in the PTP packet when the client specifies the Timestamp field offset and asserts Timestamp Insert Request.
    • Depending on the PTP device and message type, the MAC function updates the residence time in the correction field of the PTP packet when the client asserts tx_etstamp_ins_ctrl_residence_time_update and Correction Field Update. The residence time is the difference between the egress and ingress timestamps.
    • For PTP packets encapsulated using the UDP/IPv6 protocol, the MAC function performs UDP checksum correction using extended bytes in the PTP packet.
    • The MAC function recomputes and reinserts CRC-32 into PTP packets each time the timestamp or correction field is updated, even when CRC insertion is disabled using the tx_crc_control[1] register bit.
    • The format of timestamp supported includes 1588v1 and 1588v2.
    • The MAC function updates tx_egress_p2p_val[45:0] into correction field of PTP packet when the client asserts tx_egress_p2p_update.
    • The MAC function updates asymmetry value into correction field of PTP packet when the client asserts tx_egress_asymmetry_update. The asymmetry value is retrieved from configuration registers.
  • For 2-step clock synchronization, the MAC function returns the timestamp and the associated fingerprint for all TX frames when the client asserts tx_egress_timestamp_request_valid.

The following table summarizes the timestamp and correction field insertions for various PTP messages in different PTP clocks.

Table 19.  Timestamp and Correction Insertion for 1-Step Clock Synchronization
PTP Message Ordinary Clock Boundary Clock E2E Transparent Clock P2P Transparent Clock
Insert Time stamp Insert Correction Insert Time stamp Insert Correction Insert Time stamp Insert Correction Insert Time stamp Insert Correction
Sync Yes 5 No Yes5 No No Yes 6 No Yes 6
Delay_Req No No No No No Yes 6 No No
Pdelay_Req No No No No No Yes 6 No No
Pdelay_Resp No Yes 5 6 No Yes 5 6 No Yes 6 No Yes 5 6
Delay_Resp No No No No No No No No
Follow_Up No No No No No No No No
Pdelay_Resp_

Follow_Up

No No No No No No No No
Announce No No No No No No No No
Signaling No No No No No No No No
Management No No No No No No No No
5 Applicable only when 2-step flag in flagField of the PTP packet is 0.
6 Applicable when you assert the tx_etstamp_ins_ctrl_residence_time_update signal.