Intel® Agilex™ Hard Processor System Technical Reference Manual

ID 683567
Date 2/14/2023
Public

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17.6.4.5. Timestamp Error Margin

According to the IEEE1588 specifications, a timestamp must be captured at the SFD of the transmitted and received frames at the PHY interface. Because the PHY interface receive and transmit clocks are not synchronous to the reference timestamp clock (clk_ptp_ref) a small amount of drift is introduced when a timestamp is moved between asynchronous clock domains. In the transmit path, the captured and reported timestamp has a maximum error margin of two PTP clocks, meaning that the captured timestamp has a reference timing source value that is occurred within two clocks after the SFD is transmitted on the PHY interface.

Similarly, in the receive path, the error margin is three PHY interface clocks, plus up to two PTP clocks. You can ignore the error margin due to the PHY interface clock by assuming that this constant delay is present in the system (or link) before the SFD data reaches the PHY interface of the MAC.