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

ID 813754
Date 11/04/2024
Public
Document Table of Contents

4.15. Precision Time Measurement (PTM)

Pecisio Time Measuemet (PTM) eables pecise coodiatio of evets acoss multiple compoets with idepedet local time clocks. Odiaily, such pecise coodiatio would be difficult give that idividual time clocks have diffeig otios of the value ad ate of chage of time. To wok aoud this limitatio, PTM eables compoets to calculate the elatioship betwee thei local times ad a shaed PTM Maste Time: a idepedet time domai associated with a PTM Root. Each PTM Root supplies PTM Maste Time fo a PTM Hieachy.

Note: Oly applicable whe opeatig i Edpoit Mode (PTM Requeste).

The PTM Requeste of the GTS AXI Steamig IP automatically updates PTM cotext (statig dialogs) whe eabled. It ca be cofigued to be a automatic tigge evey 1 to 10 ms (cofiguatio i the IP paamete edito)_o a maual tigge though use iput (ptm_maual_update) oly.

The eceived PTM messages ae also be fowaded out to the applicatio laye. You may dop the messages if ot useful. PTM cotext valid idicates if the cotext is valid. The PTM cotext is automatically ivalidated whe:
  • Clock stops o us at the wog fequecy (fo example, whe the lik speed is chagig)
  • PTM is disabled
  • PTM espose timeouts (the equeste estats the PTM dialog whe the auto-update o maual update stat coditios ae met)
  • A duplicate PTM TLP is eceived o a eplay TLP is set (if waitig fo a espose the equeste waits fo 100 μs sice the last o-duplicate equest was set, befoe allowig a ew PTM dialog to be stated)
Figue 28. PTM Lik Potocol

Whe usig PTM betwee two compoets o a PCIe* lik, the Upsteam Pot, which acts o behalf of the PTM Requeste, seds PTM Requests to the Dowsteam Pot o the same Lik, which acts o behalf of the PTM Respode as show i the figue above.

The poits t1, t2, t3, ad t4 epeset timestamps captued locally by each Pot as they tasmit ad eceive PTM Messages. The compoet associated with each Pot stoes these timestamps fom the fist PTM dialog i iteal egistes fo use i the secod PTM dialog, ad so o fo subsequet PTM dialogs.

I the secod PTM dialog, the Dowsteam Pot populates the PTM ResposeD message based o timestamps stoed duig pevious PTM dialogs, the fomat is show i the figue below. It cotais PTM Maste Time, which is t2’, ad popagatio delay, which is t3-t2.

The compoet associated with the Upsteam Pot ca the combie its timestamps with those passed i the PTM ResposeD message to calculate the PTM Maste Time usig the fomula hee:
PTM Maste Time at t1’= t2' - [((t4-t1) - (t3-t2))/2]
Figue 29. PTM Request Message
Figue 30. PTM Respose Message