Dan's notes (Page 8)

More issues

TCXO aging part 2

The previous data I have on aging [https://blog.dan.drown.org/tcxo-rtc-hats-aging-rtc-frequency/] covered 10 days, and now I want to come back to this now that more time has passed. This data is from the same Pi Hat hardware as that post. The datasheet

PPS over USB

Goal For keeping your system clock on time, you can't beat the Pulse Per Second (PPS) signals available from $10 GPS modules. They typically have better than 100 nanosecond accuracy [https://blog.dan.drown.org/gps-module-measurements-part-3/]. GPIO PPS is one of the best ways

TCXO RTC Hats: aging & RTC frequency

I'm focusing on oscillator aging and RTC frequency in this post. See also: initial data [https://blog.dan.drown.org/tcxo-rtc-hats-initial-data/], picture [https://blog.dan.drown.org/tcxo-rtc-hats/], other stratum 2 posts [https://blog.dan.drown.org/tag/stratum2/] I've

GNUK: Open Source GPG/SSH hardware key storage

I noticed the GNUK project had support for the STM32 Blue Pill. I've been looking for an open source hardware key storage for GPG/SSH keys, so I tried it out. GNUK supports the OpenPGP smartcard protocol, and has space for 3 keys. The keys are named: "

TCXO RTC Hats: Initial data

The TCXO RTC hats [https://blog.dan.drown.org/tcxo-rtc-hats/] are collecting data. I'm focusing on the RTC part in this post. See also: other stratum 2 posts [https://blog.dan.drown.org/tag/stratum2/] Required picture This hat is on an Odroid C2. The GPS

TCXO RTC Hats

My new stratum 2 NTP server hats arrived from Macrofab today! I have a few hand soldering things to do (32khz crystal and headers), and then I can start calibrating them.

NIC interrupt coalesce impact on NTP

I noticed that my Odroid C2 system had a much higher round-trip time than I had expected. It has a gigabit ethernet built into the CPU, so it should be decent. rtt min/avg/max/mdev = 0.577/0.605/0.627/0.020 ms (10x ICMP pings) To

Temperature compensation, part 2

In the last part [https://blog.dan.drown.org/temperature-compensation/], I measured the TCXO to fit a frequency vs temperature curve. Frequency vs Temperature curve Below are the final curves that I went with for the two systems, and a comparison of the median frequency at each temperature point.

Temperature compensation

Temperature effects are usually the largest source of frequency changes in clocks. So I have three temperature sensors on my test system [https://blog.dan.drown.org/frequency-synchronization-without-phase-in-ntp/]. The sensors are: one built into the stm32 chip, a TMP36 sensor [http://www.analog.com/media/

Frequency synchronization without phase in NTP

I've been working on my high accuracy RTC project [https://blog.dan.drown.org/stm32f030-devboard-with-tcxo/]. Here's a picture of one of the two systems: Connections The TCXO devboard, BME280, and PCF RTC are all on the i2c bus. The TMP36 sensor is hidden