Chapter 5
IEEE 1588/802.1AS
IEEE 1588 is the IEEE standard for a precision clock synchronization protocol for networked measurement and control systems.
IEEE 802.1AS is the IEEE standard for local and metropolitan area networks – timing and synchronization for time-sensitive
applications in bridged local area networks. It specifies the use of IEEE 1588 specifications where applicable in the context of
IEEE Std 802.1D-2004 and IEEE Std 802.1Q-2005.
5.1 Introduction
NXP’s QorIQ platform provides hardware assist for 1588 compliant time stamping with the 1588 timer module. The software
components required to run IEEE 1588/802.1AS protocol utilizing the hardware feature are listed below:
1. Linux PTP Hardware Clock (PHC) driver
2. Linux Ethernet controller driver with hardware timestamping support
3. A software stack application for IEEE 1588/802.1AS
In this document, IEEE 1588 mentioned is IEEE 1588-2008, and IEEE 802.1AS mentioned is IEEE 802.1AS-2011.
NOTE
5.2 Device types
There are five basic types of PTP devices in IEEE 1588.
• Ordinary clock
A clock that has a single Precision Time Protocol (PTP) port in a domain and maintains the timescale used in the domain. It may
serve as a source of time (be a master clock) or may synchronize to another clock (be a slave clock).
• Boundary clock
A clock that has multiple Precision Time Protocol (PTP) ports in a domain and maintains the timescale used in the domain. It
may serve as a source of time (be a master clock) or may synchronize to another clock (be a slave clock).
• End-to-end transparent clock
A transparent clock that supports the use of the end-to-end delay measurement mechanism between slave clocks and the master
clock.
• Peer-to-peer transparent clock
A transparent clock that, in addition to providing Precision Time Protocol (PTP) event transit time information, also provides
corrections for the propagation delay of the link connected to the port receiving the PTP event message. In the presence of peer-
to-peer transparent clocks, delay measurements between slave clocks and the master clock are performed using the peer-to-
peer delay measurement mechanism.
• Management node
A device that configures and monitors clocks.
(Note: Transparent clock, is a device that measures the time taken for a Precision Time Protocol (PTP) event message to transit
the device and provides this information to clocks receiving this PTP event message.)
5.3 Two types of time-aware systems in IEEE 802.1AS
In gPTP, there are only two types of time-aware systems: end stations and Bridges, while IEEE 1588 has ordinary clocks,
boundary clocks, end-to-end transparent clocks, and P2P transparent clocks. A time-aware end station corresponds to an IEEE
1588 ordinary clock, and a time-aware Bridge is a type of IEEE 1588 boundary clock where its operation is very tightly defined,
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