[time-nuts] raspberry pi, adafruit gps & ntp

folkert folkert at vanheusden.com
Mon Jun 17 05:15:30 EDT 2013


Hi David,

> That sounds good, Folkert - perhaps you might publish the details
> somewhere? I'd like to try it myself, but my Linux and C knowledge
> is limited.

Here it is:
http://vanheusden.com/time/rpi_gpio_ntp/

Please let me know if anything is unclear: I'll then enhance e.g. the
readme.txt and such.

> For comparison, on three RPi cards here with modified kernels to get
> PPS from a GPIO pin, using ntpq -pn I see jitter values of 0.002,
> 0.002 and 0.002/0.004.  The 0.002 seems to be near the sys_jitter
> limit as reported from ntpq -c rv.

That's indeed better. The results I see are probably also influenced by
the fact that this RPI also does other things (software defined radio,
camera and measuring the light intensity outside).

> Cards 1 and 2 are just doing NTP, the third card is running a data
> collector processing signals from a DVB receiver stick, and sending
> the derived data over a Wi-Fi link to a PC running Plane Plotter
> using the dump1090 program. This gives a CPU load around 35%.  It
> would be interesting to know how your version handles a busy RPi.

Hmmm, I'll see if I can setup an RPI which only does the time keeping
and see if that gives better results.


Folkert van Heusden

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