On 10/16/2012 05:06 PM, x...@darksmile.net wrote:
My goal is to design a custom board for the Pi and mount a GPS receiver
on it. With this combination, I should be able to configure NTP for the
Pi and thus have the Pi act as a Stratum 1 NTP server.
The new RasberryPI has 512MB memory so it should be fine for running
just ntpd.
Question: What GPS timing module should I go with? No more Motorola
Oncore so what's best right now? Who sell modules? What are the price
ranges?
It's not a terrible idea, but the RPI has a USB ethernet transceiver so
in addition to the latency/jitter of the ethernet it also has the
latency/jitter of the USB. I've also heard of stability problems just
keeping it running for weeks to months so you should integrate some kind
of watchdog timer if you can. The actual GPS module doesn't matter much
since NTP will smooth out even the worst GPS jitter. I have heard
second-hand (or third-hand or fourth-...) that some have a significant
persistent delay and that could be more of a problem. If you want to go
for a timing-oriented receiver you can get a used Trimble Resolution T
from ebay but they have a 2mm pitch header.
You will want to house the RPI and GPS receiver in a box where it will
not be subject to wide temperature swings, insulated and shielded from
drafts. It would also be interesting to upgrade the main oscillator to a
temperature-compensated model so NTP doesn't have to work as hard to
keep the frequency locked.
Personally I would recommend getting a more robust single-board
computer, e.g. a PC Engines ALIX or Olimex olinuxino. RPI is cheap but
hard to source, not open-source, and does not have good long-term
prospects due to the microprocessor being used. Most of the attention is
due to deliberate publicity by the manufacturer and not novelty or
merit. If you must use the cheapest board then by all means do so, but
just know there is better available for not much more.
Happy ticking,
-- m. tharp
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
