Figure 20-8. Networked Time Synchronization
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
As shown in Figure 20-8 on page 1441, 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
1441
June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller