Topic

gps

A collection of 27 issues

Measuring Asymmetric latency via NTP, part 3

Part 1 [https://blog.dan.drown.org/measuring-asymmetric-latency-via-ntp/], Part 2 [https://blog.dan.drown.org/measuring-asymmetric-latency-via-ntp-part-2/] Varying round trip times Asymmetric latency changes NTP's calculated clock offsets. What do the offsets look like when two clocks are in sync (or always within ~200us) and the latency varies? SMQ

Measuring Asymmetric latency via NTP, part 2

See the first part for the math [https://blog.dan.drown.org/measuring-asymmetric-latency-via-ntp/] Let's use a third party (stratum 2) observer to compare the stratum 1 NTP clocks. Round trip times First, a graph of the $rtt times from the third party to various stratum 1 NTP clocks.

Measuring Asymmetric latency via NTP

Goal Learn more about the latency characteristics of my cable connection. Starting point I have a stratum 1 NTP server at home. Below is a graph of its performance. The offset between the GPS clock and the server's clock is in red. The two clocks are within +/-

Navspark NTP stratum 0 clock

Project Goal I want to create a stratum 0 NTP clock that does not require soldering or any special hardware. It should only require a USB port and software. It should have at least 125 microsecond accuracy. How? I created a Navspark firmware to print a timestamp on the serial

Navspark UART/USB bridge

I created a program on the Navspark to send characters at 150 microsecond intervals and then received them on a PC. Below is a histogram of how long it took between characters: The red boxes are how long it took for the UART/USB bridge to send one character in

Navspark timer drift, #2

Second run, this time comparing the Navspark's internal CPU clock against the GPS time. Samples of both clocks are taken once per second, and the amount of time that has passed is calculated for both. The ideal CPU clock would be a perfectly horizontal line at 0.000

Navspark timer drift

The Navspark is a microcontroller with a GPS peripheral. It runs the GPS navigation/timing code as a binary-only library, and uses the Arduino IDE/environment. I have custom code printing timestamp markers on the Navspark, and I'm measuring the timestamp of the first byte of each line