fallback pps source

[Hal Murray]

>> You could make your primary PPS as "prefer".  Then other sources only
>> get uses when it is down or obviously crazy.

> Oh indeed! That will work of course. Thanks! 

There are 2 ways to get PPS data into ntpd.  One is via gpsd.  The other 
is via the PPS driver.

The PPS driver needs another driver to tell it which second a pulse goes 
with.  It does that by stealing the prefer command.

So Gary's suggestion will probably work if you are using gpsd.  I expect 
troubles if you try it without gpsd.

If you do try it, please let us know if it works.  You can make the 
primary GPS signal go away by unplugging the cable or unplugging the 
antenna.  Putting the antenna in a crappy location so the signal fades in 
and out might be a more interesting test.  Adjust crappyness for 
interesting results.


-- 
These are my opinions.  I hate spam.