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Linux Time Syncrhronization

Many applications in factory automation, test and measurement, and telecommunications require very close time synchronization. The usage case for this is often scenarios where they have multiple boards transmitting on the same RF channel and they want to synchronize the system clocks to a precision that allows the boards to Time Division Multiplex (TDM) the use of the transmitters so they are not producing collisions and thus maximizing RF throughput as this is the most efficient way of utilizing available bandwidth.

There are two common solutions to this problem:

Time synchronization via IEEE 1588 Precision Time Protocol (PTP) (Ethernet)

The purpose of the IEEE 1588 Precision Time Protocol (PTP) is to synchronize the time between different nodes on an Ethernet network.

The Linux kernel has IEEE 1588 PTP support for a handful of ethernet devices that offer this feature including the Freescale IMX6 FEC which is used as eth0 on the majority of the Gateworks Ventana boards including the GW51xx, GW52xx, GW53xx, and GW54xx (Note GW5520 does not use the IMX6 FEC and instead provides 2x full GigE capable PCIe based MAC/PHY devices so it lacks IEEE 1588 hardware support).

In hardware PTP the ethernet MAC is responsible for getting and setting the timestamps to remove latency of the queuing and network stack which provides the best accuracy.

The Linux PTP project is an implementation of the IEEE 1588 for Linux featuring:

The linuxptp package is install on the Gateworks Ventana Yocto v1.8 BSP.

Example usage on a GW54xx:

References:

Time synchronization via PPS (Pulse-Per-Second) (GPS)

One handy feature of an on-board GPS is that it can deliver Pulse-Per-Second (PPS) signal. This signal can be used to get a high-precision time reference that an application can use to adjust system clock time. Common use is to configure the Network Time Protocol Daemon (NTPD) with a PPS source to obtain a wallclock-time with sub-millisecond synchronization to UTC.

See the GPS page for more info

Last modified 2 years ago Last modified on 08/27/15 16:41:56
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