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Slave Clock Time
Master Clock Time
t
1
t
4
t
2m
t
2
t
2
t , t
1
2
t , t
1
2
3
, t
t , t
1
2
3
4
, t , t
t
3
t
3m
time
Delay Resp message
containing value of t
4
Follow_Up message
containing value of t
1
Sync message
Delay_Req message
Data at
Slave Clock
Functional Description
916
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Ethernet Controller
Figure 15-10. Networked Time Synchronization
As shown in
, the PTP uses the following process:
1. The master broadcasts the PTP Sync messages to all its nodes. The Sync message contains the
master's reference time information. The time at which this message leaves the master's system is t1.
This time is captured at the MII interface.
2. The slave receives the Sync message and also captures the exact time, t2, using its timing reference.
3. The master sends a Follow_Up message to the slave, which contains t1 information for later use.
4. The slave sends a Delay_Req message to the master, noting the exact time, t3, at which this frame
leaves the MAC.
5. The master receives the message, capturing the exact time, t4, at which it enters its system.
6. The master sends the t4 information to the slave in the Delay_Resp message.
7. The slave uses the four values of t1, t2, t3, and t4 to synchronize its local timing reference to the
master's timing reference.
Most of the PTP implementation is done in the software above the UDP layer. However, the hardware
support is required to capture the exact time when specific PTP packets enter or leave the Ethernet MAC.
This timing information is captured and returned to the software for the proper implementation of PTP with
high accuracy.