How to set time in nanoseconds?

Question

I have a Raspberry Pi with a GPS module connected to it. Since all GPS satellites have very precise atomic clocks on them, I would like to synchronize the Pi's clock to the satellites' clocks. I know how to get the date and time from the satellites, and set my Pi's time with:

sudo date -s "MAR 14 2016 14:53:09"

But that is only accurate to the seconds, I would like to at least get milliseconds, but I would prefer nanoseconds.

I know that date +%s%N returns time in nanoseconds.

How do I set the time in nanoseconds?

Too slow, no better resolution than getting it via NTP. The capability of doing that is also dependent on the brand, please post it to see if someone answers. — Rui F Ribeiro, Mar 14 '16 at 20:16
@RuiFRibeiro the converter or the GPS module? All I know is that the module runs at a baudrate of 9600. — Patrick Cook, Mar 14 '16 at 20:17
If it's accurate time you're after, suggest you look into PTP - http://linuxptp.sourceforge.net/ — steve, Sep 24 '16 at 21:42

score 6 · Accepted Answer · edited Mar 01 '18 at 12:01

By the time the data reaches your PC via the USB/RS232 interface, the resolution and accuracy won't be any good. At the end of the day, without dedicated equipment, it is better to stay with NTP.

From this GPS synchronization tutorial

There are many cheap GPS receivers available in the market. Most of them use either an RS232, or USB connection to send their information to the attached computer. Although the clock inside the receiver itself runs with an accuracy of some nanoseconds, the transfer of the data to the computer causes such a large delay, that in practice it is not possible to synchronize the clock of the local computer with that signal with an accuracy of better than a handful of milliseconds. That kind of accuracy can also be obtained by connecting to a freely available NTP time server over the internet. Only GPS devices which have a special fast and accurate synchronization method with the computer can be used as a time synchronization device. The most expensive and accurate way to do this is to use a GPS receiver which fits in a local PCI or PCIex slot of the computer. But these cards are very expensive and not widely available. The other solution is to use the slow and inaccurate RS232 or USB interface to send general data and do the time synchronization with a pulse.

As @dfc correctly points out, RS232 with PPS does the job. However, the device has to support it.

On most GPS devices with pulse capability, the pulse is sent once every second, starting at the beginning of every new second. This is why these GPS devices are often referred to as GPS with PPS, for pulse per second.

Unfortunately there are not a large number of GPS receivers which have the extra PPS output. I am using Garmin GPS receivers in Kazakhstan for my tourism activities and I have therefore first looked at the available devices from this manufacturer. Currently there are two Garmin GPS receivers which may be used with a direct connection with a computer: the Garmin GPS 16x LVS and the Garmin GPS 18x LVC. They both work on a supply voltage of +5 Volt which is directly available from a computer, they both send the general data in NMEA protocol over an RS232 interface and they both have a PPS output.

RS232 with PPS is not slow and innacurate. – dfc Mar 15 '16 at 18:14 — dfc, Mar 15 '16 at 18:14
Indeed, I had not added it for the answer. thanks. – Rui F Ribeiro Mar 15 '16 at 18:37 — Rui F Ribeiro, Mar 15 '16 at 18:37

How to set time in nanoseconds?

1 Answers1