Ptp Link Delay Measurement; Ptp Time Synchronization Messaging; Table 43: Ptp Link Delay Measure Roles - Broadcom NetXtreme/NetLink BCM5718 Series Programmer's Manual

BCM5718 Programmer's Guide

PTP Link Delay Measurement

At the completion of the Delay Request/Response exchange, the delay requester uses four timestamps (t1, t2,
t3, t4) to compute the link delay. The link delay is computed as the average of the two one-way delays using the
following formula:
T delay = [(t2 – t1) + (t4 – t3)] / 4
Assume that both nodes contain a NetXtreme Time-Synch Capable NIC.
software component and the Time-Synch capable NIC hardware play during the above exchange.
Delay Requester
Host Software
1 TX PTP Delay Request
packet- mark capture →
2 –
3a –
4 ← Receive Packet, Read
RX Time Stamp Reg
3b Receive packet
5 Collect t1, t2, t3, and t4 to
compute T delay.

PTP Time Synchronization Messaging

The slave device then uses the link delay (Tdelay) and the Sync Message timestamps (t1, t2) to calculate the
time offset it needs to compensate its local clock by using the following equation:
Tslave-offset = t2 – t1 – Tdelay
Assume that both nodes contain a NetXtreme Time-Synch Capable NIC.
roles the PTP software component and Time-Synch capable NIC hardware play during above exchange.
Broadcom
®
January 29, 2016 • 5718-PG108-R

Table 43: PTP Link Delay Measure Roles

NIC Hardware
Capture TX stamp (t1) → –
–
–
Receive and identify PTP
Delay Response packet,
then capture RX Time
Stamp (t4) ←
–
–
Table 43
Delay Responder
NIC Hardware
→ Receive and identify
PTP delay request
packet, then capture RX
Time Stamp (t2)
Capture TX Time Stamp
(t3) ←
–
← (pass through)
–
Table 44 on page 154
NetXtreme Time Sync Assist
describes the roles the PTP
Host Software
–
→ Receive packet, Read
RX Time Stamp Reg.
TX PTP Delay Response
packet with embedded
(t2) value — mark
capture ←
–
TX PTP Delay Response
Follow-up packet with
embedded (t3) value
–
describes the
Page 153