Time Stamp Reference Point; Priority Message Support; Follow_Up Message - Intel IXP45X Developer's Manual

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synchronization delays, the actual timestamp will be slightly later than the desired
reference point. However, allowing for 1 pclk synchronization jitter, this is a fixed delay,
easily nulled out in the software portion of the algorithm. This fixed delay is dependent
on the 10/100 MHz selection at the PHY and therefore software needs to be able to
access this information from each of the PHYs via the shared Management Data
Interface (MDI).
When a Sync or Delay_Req messages is detected, the timestamp that was captured at
the SFD in the snapshot register is frozen or "locked" until acknowledged by the
firmware.
Each message is detected by identifying key bytes in the packet. The byte offsets
identified below are numbered starting with the 1
numbering begins at 0. Therefore "byte 74" refers to the 75
Figure 189. Time Stamp Reference Point

Priority Message Support

19.3.1
Since there exists a wide variety of data on an industrial Ethernet network, including
both time-critical and non-time-critical data, it is desirable to support "Tagged MAC
Frames" from 802.3 which define priority based messages. A Tagged MAC Frames is
identified by the "length/type" field. If byte 12 = 0x81 and byte 13=0x00, then the
message is using the Tagged MAC Frame format, in which 4 additional bytes need to be
accounted for in the header. Therefore, if a Tagged MAC Frame is detected, all the byte
offsets mentioned below are incremented by 4.
19.3.2 Sync Message
Firmware in a time master transmits a multicast Sync message periodically over the
network at 1, 2, 8, 16, or 64 second intervals. A Sync message is defined as a value of
0x00 in byte 74 of the Ethernet frame after the start of frame delimiter.
The TSync logic will monitor the MII signals, detect when the channel has transmitted
or received a Sync message, and lock the timestamp. Furthermore, the TSync logic
captures the Sequence ID and Source UUID if a Sync message is received by a channel
configured as a time slave.

Follow_Up Message

19.3.3
Firmware in a time master transmits the timestamp, captured during a previously sent
Sync message, using a multicast Follow_Up message. No time stamping is done by the
master or slave with the Follow_Up message. A Follow_Up message is defined with a
value of 0x02 in byte 74 of the Ethernet frame after the start of frame delimiter.
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Intel IXP45X and Intel IXP46X Product Line of Network Processors
Developer's Manual
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IXP45X and Intel IXP46X Product Line of Network Processors—Time Synchronization
Preamble
Octet
1 1 1
0 0 0 0
st
byte after the SFD and the
Message Timestamp
Point
Ethernet
Start of Frame
Delimiter
1 1 1 1 1
0 0
bit time
Hardware Assist (TSYNC)
th
byte after the SFD.
First Octet
following
Start of Frame
0 0 0 0 0 0 0
B4320-01
August 2006
Order Number: 306262-004US