AXI Streaming Intel® FPGA IP for PCI Express* User Guide

ID 790711
Date 2/12/2024
Public

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4.20. Precision Time Measurement (PTM) [F/R-Tiles Only]

Note: This feature is planned for a future release.

Precision Time Measurement (PTM) enables precise coordination of events across multiple components with independent local time clocks. Ordinarily, such precise coordination would be difficult given that individual time clocks have differing notions of the value and rate of change of time. To work around this limitation, PTM enables components to calculate the relationship between their local times and a shared PTM Master Time, which is an independent time domain associated with a PTM Root. Each PTM Root supplies the PTM Master Time for a PTM Hierarchy.

Note: Only applicable when operating in Endpoint Mode (PTM Requester).
The endpoint generates a PTM request message that goes to the Root Complex. The PTM requester updates the time stamp t1 when generating a request. It updates the time stamp t4 when it receives the response. Refers to the PCIe Base Specification for t1/t4 definitions. Requester automatically updates the PTM context (starting dialogues) when enabled using all or any of the following:
  • Automatic trigger every 10ms - always enabled
  • Manual trigger through user input (ptm_manual_update)
The received PTM messages are also forwarded to the application layer. You may drop the messages if not useful. The PTM context valid indicates if the context is valid. The PTM context is automatically invalidated when:
  • Clock stops or runs at the wrong frequency (for example, when the link speed is changing), or
  • PTM is disabled, or
  • PTM response times out (the requester restarts the PTM dialogue when the auto-update or manual update start conditions are met), or
  • A duplicate PTM TLP is received or a replay TLP is sent (if waiting for a response, the requester waits for 100µs since the last non-duplicate request was sent before allowing a new PTM dialogue to be started).
The committed PTM accuracy targets for F/R-Tile are:
  • +/-50ns for the common clock scheme.
  • +/100ns for the separate clock scheme.