Dan's notes (Page 10)

More issues

TCXO + Beaglebone Black

I've added support for an external clock (TCLKIN) to the Beaglebone Black timer driver [https://blog.dan.drown.org/beaglebone-black-timer-capture-driver/]. Setup I used what I had on hand to test it. I setup a Navspark microcontroller to send a ~1MHz PWM (code here [http://dan.drown.org/bbb/

Beaglebone Black timer capture driver

More info on: Hardware [https://blog.dan.drown.org/beaglebone-black-gpstemperature-cape/], Kernel Driver software [https://github.com/ddrown/pps-gmtimer] The Beaglebone Black has a hardware timer capture. This means it can save the couter value at the time an input edge happens. Since it has a 24MHz clock, the timer has

Beaglebone Black GPS+Temperature cape

I moved my Beaglebone Black GPS+Temperature [https://blog.dan.drown.org/beaglebone-black-ntpgps-server/] setup from a breadboard to a proto cape. The soldering isn't great, and the wire I had on had was much too thick for this. The back, with the DS18B20 sensor (ends up near the

SB6183 vs DG1670A latency

See also: SB6183 dropping IPv6 traffic [https://blog.dan.drown.org/sb6183-dropping-ipv6-traffic/] Comparing latency in cable modems: SB6183 (16 channel DOCSIS 3 modem only) vs DG1670A (16 channel DOCSIS 3 modem+router combo, in bridge mode) Arris DG1670A Average latency of 100 ICMP echo replies to the default gateway: 20.

Beaglebone Black NTP/GPS Server, Temperature Compensation part 2

See the Part 1 of Temperature Compensation [https://blog.dan.drown.org/beaglebone-black-ntpgps-server-temperature-compensation/] or the hardware setup [https://blog.dan.drown.org/beaglebone-black-ntpgps-server/] Overview In part 1, I did a trial run of chrony's temperature compensation and got a pretty good result. In this part, I collected more

Beaglebone Black NTP/GPS Server, Temperature Compensation part 1

See also: The hardware/software setup [https://blog.dan.drown.org/beaglebone-black-ntpgps-server/] or part 2 [https://blog.dan.drown.org/beaglebone-black-ntpgps-server-temperature-compensation-part-2/] Overview Chrony (the NTP server software) has temperature compensation built in, using a quadratic forumla to estimate the effect of temperature changes have on the speed of the local

Beaglebone Black NTP/GPS server

Goals I wanted to experiment with using temperature measurement to augment a NTP stratum 1 server. I started with a very similiar setup to this one [https://web.archive.org/web/20131209092059/http://the8thlayerof.net/2013/12/08/adafruit-ultimate-gps-cape-creating-custom-beaglebone-black-device-tree-overlay-file/] . [Edit: the8thlayerof.net is gone, link changed to archive.org]. This

Stratum 2 NTP over a Cable Modem

Goals I have a Stratum 1 NTP server at home, and ideally I'd like to join the ntp pool as a server. The problem is, my home connection isn't up to this task. My IP is dynamic, there's an asymmetric latency built in, and

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.