Low Latency 100-Gbps Ethernet IP Core User Guide

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ID 683160
Date 4/15/2021
Public
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3.2.14.5. PTP Timestamp and TOD Formats

The LL 100GbE core supports a 96-bit timestamp (V2 format) or a 64-bit timestamp (correction-field format) in PTP packets. The 64-bit timestamp and TOD signals of the IP core are in an Intel-defined 64-bit format that is distinct from the V1 format, for improved efficiency in one-step processing correction mode. Therefore, if your system need not handle any packets in one-step processing correction mode, you should turn off the Enable 64b Time of Day Format parameter .

You control the format or formats the IP core supports with the Enable 64b Time of Day Format and Enable 96b Time of Day Format parameters . If you turn on Enable 96b Time of Day Format , your IP core can support two-step processing mode, one-step processing insertion mode, and one-step processing correction mode, and can support both V1 and V2 formats. You can turn on Enable 64b Time of Day Format and turn off Enable 96b Time of Day Format to support one-step processing correction mode more efficiently. However, if you do so, your IP core variation cannot support two-step processing mode and cannot support one-step processing insertion mode. If you turn on both of these parameters, the value you drive on the tx_estamp_ins_ctrl_timestamp_format or tx_etstamp_ins_ctrl_residence_time_calc_format signal determines the format the IP core supports for the current packet.

The IP core completes all internal processing in the V2 format. However, if you specify V1 format for a particular PTP packet in one-step insertion mode, the IP core inserts the appropriate V1-format timestamp in the outgoing packet on the Ethernet link.

V2 Format

The IP core maintains the time-of-day (TOD) in V2 format according to the IEEE specification:

  • Bits [95:48]: Seconds (48 bits).
  • Bits [47:16]: Nanoseconds (32 bits). This field overflows at 1 billion.
  • Bits [15:0]: Fractions of nanosecond (16 bits). This field is a true fraction; it overflows at 0xFFFF.

The IP core can receive time-of-day information from the TOD module in V2 format or in 64-bit TOD format, or both, depending on your settings for the Enable 64b Time of Day Format and Enable 96b Time of Day Format parameters .

V1 Format

V1 timestamp format is specified in the IEEE specification:

  • Bits [63:32]: Seconds (32 bits).
  • Bits [31:0]: Nanoseconds (32 bits). This field overflows at 1 billion.

Intel 64-Bit TOD Format

The Intel 64-bit TOD format is distinct from the V1 format and supports a longer time delay. It is intended for use in transparent clock systems, in which each node adds its own residence time to a running total latency through the system. This format matches the format of the correction field in the packet, as used in transparent clock mode.

  • Bits [63:16]: Nanoseconds (48 bits). This field can specify a value greater than 4 seconds.
  • Bits [15:0]: Fractions of nanosecond (16 bits). This field is a true fraction; it overflows at 0xFFFF.

The TOD module provides 64-bit TOD information to the IP core in this 64-bit TOD format. The expected format of all 64-bit input timestamp and TOD signals to the IP core is the Intel 64-bit TOD format. The format of all 64-bit output timestamp and TOD signals from the IP core is the Intel 64-bit TOD format. If you build your own TOD module that provides 64-bit TOD information to the IP core, you must ensure it provides TOD information in the Intel 64-bit TOD format.

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