UM10503
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User manual
Rev. 1.3 — 6 July 2012
729 of 1269
NXP Semiconductors
UM10503
Chapter 26: LPC43xx Ethernet
As shown in
, the propagation delay is calculated in the following way:
1. Port-1 issues a Pdelay_Req message and generates a timestamp, t1, for the
Pdelay_Req message .
2. Port-2 receives the Pdelay_Req message and generates a timestamp, t2, for this
message.
3. Port-2 returns a Pdelay_Resp message and generates a timestamp, t3, for this
message.
To minimize errors because of any frequency offset between the two ports, Port-2
returns the Pdelay_Resp message as quickly as possible after the receipt of the
Pdelay_Req message. The Port-2 returns any one of the following:
–
The difference between the timestamps t2 and t3 in the Pdelay_Resp message.
–
The difference between the timestamps t2 and t3 in the Pdelay_Resp_Follow_Up
message.
–
The timestamps t2 and t3 in the Pdelay_Resp and Pdelay_Resp_Follow_Up
messages respectively.
4. Port-1 generates a timestamp, t4, on receiving the Pdelay_Resp message.
5. Port-1 uses all four timestamps to compute the mean link delay.
Fig 70. Propagation Delay Calculation in Clocks Supporting Peer-to-Peer Path Correction
P2P TC A
Delay
Requester
Time
P2P TC B
Delay
Responder
Time
Pdelay_Req
Pdelay_Resp
t
1
t
4
t
3
t
2
Timestamps
known by Delay
Requester
t
1
t
1
,t
4
t
1
,
t
2
,
t
3
,
t
4
Pdelay_Resp_Follow_Up:
t
2
,
t
3
t
BA
t
AB