[gpsd-dev] RFC 2783

[Gary E. Miller]

Yo Eric!

I have been looking at the ntpd RFC 2783 enabled drivers hoping to learn
something from them.  I found the opposite.  gpsd does a much better
job with RFC 2783 than ntpd.  Except for one thing ntpd does better.

Gpsd auomatically configures the GPS serial port for PPS, then
automatically detects the resulting /dev/ppsX device. gpsd then passes PPS
data to ntpd for all offsets from system clock to PPS clock.

ntpd does none of that.  In the configuration file you tell ntpd which of
/dev/pps[0-3] to use.  Before ntpd will use the PPS input the ntpd time and
system time must be within +/- 400 mSec.  That may be hard to do for 
a GPS and gpsd does not require that.

We are getting a lot of pull from the embedded community to support
manually configuring the /dev/ppsX.  For example, there are many GPS for
RasPi that put PPS on GPIO pin 4.  Adafruit claims to have sold 10,000
plus GPS for RasPi configure this way.  There is no way for the kernel
or for gpsd to know the association between GPIO 4 and the serial GPS.

For those Adafruit, and other, users we need a way to specify a
/dev/ppsX manually.  This also solves the problem on other OS that
do not allow Linux like determination of serial device to PPS device
mapping.

How about something like this:

        gpsd -n /dev/ttyUSB0 -p /dev/pps0

Ideas?

I have an adafruit on order so I can test:

http://www.adafruit.com/products/2324

RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
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