Data Sheet

Ethernet Controller I210 —Inline Functions
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7.8 Time SYNC (IEEE1588 and IEEE 802.1AS)
7.8.1 Overview
IEEE 1588 addresses the clock synchronization requirements of measurement and control systems. The
protocol supports system-wide synchronization accuracy in the sub-microsecond range with minimal
network and local clock computing resources. The protocol is spatially localized and allows simple
systems to be installed and operate.
The IEEE802.1AS standard specifies the protocol used to ensure that synchronization requirements are
met for time sensitive applications, such as audio and video, across bridged and Virtual Bridged Local
Area Networks (VBLAN) consisting of LAN media where the transmission delays are almost fixed and
symmetrical. For example, IEEE 802.3 full duplex links. This includes the maintenance of synchronized
time during normal operation and following addition, removal, or failure of network components and
network re-configuration. It specifies the use of IEEE 1588 specifications where applicable.
Activation of the I210 Time Sync mechanism is possible in full duplex mode only. No limitations on wire
speed exist, although wire speed might affect the accuracy. Time Sync protocol is tolerant of dropping
packets as well as missing timestamps.
7.8.2 Flow and Hardware/Software Responsibilities
The operation of a PTP (Precision Time Protocol) enabled network is divided into two stages,
initialization and time synchronization. These stages are described in the sections that follow
emphasizing hardware and software roles.
7.8.2.1 Initialization Phase
At the initialization stage the software on every master enabled node starts by sending Sync packets
that include its clock parameters. Upon reception of a Sync packet a node, the software on any
potential master, compares the received clock parameters to its own parameters. If the received clock
parameters of a peer are better, the software transits to Slave state and stops sending Sync packets.
When in slave state, the software selects a particular master. It compares continuously the received
Sync packet to its selected master. If the received Sync packets belong to a different master with better
clock parameters, the software on the slave switches to the new master. Eventually only one master
(with the best clock parameters) remains active while all other nodes act as slaves listening to that
master. Every node has a defined Sync packet time-out interval. If no Sync packet is received from its
chosen master clock source during the interval the software on the master enabled nodes transit back
to master state at initialization phase. Note that there are more than one option for the above flow. For
example, one node could be set statically as the master while all other notes are set as slaves listening
to that master.
7.8.2.2 Time Synchronization Phase
There are two phases to the synchronization flow: At the beginning, the slave calibrates its clock to the
master and then it performs the complete synchronization.
7.8.2.2.1 2-step Clocks Calibration Procedure
The master send SYNC packets periodically (in the order of 10 packets per second). These packets are
followed by Follow_UP packets that indicate the transmission time. The slave captures the reception
time of these SYNC packets. Together with the Follow_UP packets the slave holds the SYNC packet