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Note The 802.1AS time synchronization protocol is supported only on Linux RT targets. |
The IEEE 802.1AS generalized precision time protocol (gPTP) is a standard based on IEEE 1588 that is better optimized for time-sensitive applications. Like 1588, 802.1AS controls synchronization across a series of nodes connected by Ethernet cables, switches, and bridges by automatically designating a grandmaster clock using the Best Master Clock algorithm (BMCA). The grandmaster clock then serves as the source of time to slave devices (devices not elected as the 1588 grandmaster) across the network.
Each distributed device runs the BMCA to determine the highest ranking, most accurate device clock on the network, which automatically becomes the grandmaster. If the grandmaster clock leaves the network or is no longer the most accurate clock on the network, the BMCA selects a new grandmaster. The BMCA defines a standard set of clock characteristics—such as the origin of a clock's time source and the stability of the clock's frequency—and then assigns a value to each clock in order to determine the grandmaster. The BMCA also takes into account user-defined priority values, which you can set using the 802.1AS Priority1 and 802.1AS Priority2 properties.
One of the main differences between 802.1AS and 1588 is that 802.1AS requires 802.1AS-capable network switches and network interfaces providing hardware-assisted timestamping in order to operate. You can determine whether or not a device is capable of running 802.1AS using the AS Capable property.