Embedded NTP client/NTP interleaved mode
NTP client with hardware timestamps
Topic
stm32
A collection of 23 issues
GPS module measurements, part 2
After the previous tests [https://blog.dan.drown.org/gps-module-measurements/], I ordered
another GPS antenna to improve the signal conditions.
They're just the cheap puck style antennas with SMA connectors ($10 on Amazon),
and I've put them on my windowsill.
There's something wrong with
GPS module measurements
Starting point
I got a u-blox NEO-6M and I wanted to compare it to my NS-T. Since I don't have
a frequency counter, I decided to try creating one myself.
The hardware I have on hand is a 72MHz STM32 devboard. I used the input capture
hardware on
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 to get that timing
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 been letting these boards run to
GNUK: Open Source GPG/SSH hardware key storage
I noticed the GNUK [https://www.fsij.org/category/gnuk.html] project had support
for the STM32 Blue Pill [http://wiki.stm32duino.com/index.php?title=Blue_Pill].
I've been looking for an open source hardware key storage for GPG/SSH keys, so I
tried it out.
GNUK
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 module on
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.
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. The
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/en/technical-documentation/data-sheets/TMP35_36_