LAN9313 datasheet(134/398 Pages) SMSC

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Three Port 10/100 Managed Ethernet Switch with MII

Datasheet

Revision 1.2 (04-08-08)

134

SMSC LAN9313/LAN9313i

DATASHEET

Chapter 10 IEEE 1588 Hardware Time Stamp Unit

10.1

Functional Overview

The LAN9313/LAN9313i provides hardware support for the IEEE 1588 Precision Time Protocol (PTP),

allowing clock synchronization with remote Ethernet devices, packet time stamping, and time driven

event generation. Time stamping is supported on all ports, with an individual IEEE 1588 Time Stamp

module connected to each port via the MII bus. Any port may function as a master or a slave clock

per the IEEE 1588 specification, and the LAN9313/LAN9313i as a whole may function as a boundary

clock.

A 64-bit tunable clock is provided that is used as the time source for all IEEE 1588 time stamp related

functions. An IEEE 1588 Clock/Events block provides IEEE 1588 clock comparison based interrupt

generation and time stamp related GPIO event generation. Two LAN9313/LAN9313i GPIO pins

(GPIO[8:9]) can be used to trigger a time stamp capture when configured as an input, or output a

signal from the GPIO based on an IEEE 1588 clock target compare event when configured as an

output. Section 10.1.2, "Block Diagram" describes the various IEEE 1588 related blocks and how they

interface to other LAN9313/LAN9313i functions.

All features of the IEEE 1588 hardware time stamp unit can be monitored and configured via their

respective configuration and status registers. A detailed description of all IEEE 1588 CSRs is included

in Section 13.1.4, "IEEE 1588," on page 164.

10.1.1

IEEE 1588

IEEE 1588 specifies a Precision Time Protocol (PTP) used by master and slave clock devices to pass

time information in order to achieve clock synchronization. Five network message types are defined:

Sync

Delay_Req

Follow_Up

Delay_Resp

Management

Only the first four message types (Sync, Delay_Req, Follow_Up, Delay_Resp) are used for clock

synchronization. Using these messages, the protocol software may calculate the offset and network

delay between time stamps, adjusting the slave clock frequency as needed. Refer to the IEEE 1588

protocol for message definitions and proper usage.

A PTP domain is segmented into PTP sub-domains, which are then segmented into PTP

communication paths. Within each PTP communication path there is a maximum of one master clock,

which is the source of time for each slave clock. The determination of which clock is the master and

which clock(s) is(are) the slave(s) is not fixed, but determined by the IEEE 1588 protocol. Similarly,

each PTP sub-domain may have only one master clock, referred to as the Grand Master Clock.

PTP communication paths are conceptually equivalent to Ethernet collision domains and may contain

devices which extend the network. However, unlike Ethernet collision domains, the PTP

communication path does not stop at a network switch, bridge, or router. This leads to a loss of

precision when the network switch/bridge/router introduces a variable delay. Boundary clocks are

defined which conceptually bypass the switch/bridge/router (either physically or via device integration).

Essentially, a boundary clock acts as a slave to an upstream master, and as a master to a down stream

slave. A boundary clock may contain multiple ports, but a maximum of one slave port is permitted.

For more information on the IEEE 1588 protocol, refer to the National Institute of Standards and

Technology IEEE 1588 website:

http://ieee1588.nist.gov/

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