Re: [gpsd-dev] RFC 2783

[Frank Nicholas]

I have this adafruit GPS (https://www.adafruit.com/product/746), and had it connected to a RaspberryPi for a year or two.  I used NTPd directly.  Nifty piece of hardware and is extremely reliable.  It has an external antenna connector that I'm using.  It came with a battery holder that I never used.  It locks quick, even with a long off, cold start.

The adafruit GPS is currently attached to my BSD based pfSense router as an NTP server (no GPSd).  I'll probably move it back to a Pi and put one of the USB GPS's I just received on the pfSense box (less wires in that area).  I'll then have 2 x PPS enabled GPS NTP servers at home.  Any advantages to 2 x on the same LAN?  What should I look for to dial them in, or should I just let NTP on the clients figure it out?

On Tue, Mar 10, 2015 at 2:45 PM, Gary E. Miller <address@hidden> wrote:

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
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588