Testing...

[Hal Murray]

Am I the only one actually running this code?

If you are, how is it going and what systems are you running it on?

If you aren't already running it, what's keeping you from running it on your 
home PC and/or laptop?

Anybody testing refclocks?

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How many of you have good refclocks to test with?  There is a lot of testing 
that gets more interesting if you have a known-good place to stand while 
looking around.  It also helps to test the refclock code. Disclaimer:  It can 
also be a time sink.

Modern GPS chips are pretty good.  They will probably work inside a house.  
They won't work in a machine room (too much EMI) and probably not down in a 
basement (not enough signal).  A window sill probably helps.  A steel frame 
probably hurts.  Reflective metalized windows are deadly.


For many years, I've been searching for a good low cost GPS unit with no 
assembly required.  I still haven't found one.

My cutoff for low cost is $50.  YMMV  [1]

"Common knowledge" is that for a "good" setup, you need PPS on a real serial 
port.  That eliminates a some modern PCs and laptops which have switched to 
USB.

There are lots of low cost GPS units available.  Most of the ones that pass 
the no assembly test use USB.  All but one of those don't even come close to 
passing the "good" test because they don't have PPS.  (You should be able to 
get almost as good timing from the serial data stream, but most of the 
firmware on GPS units is crappy for timing.)

Eric got one vendor to wire up the PPS signal from the GPS chip to the 
appropriate modem control pin on the serial-USB chip.  I'd call it better 
rather than good.  USB is polled at the hardware level.  Timing isn't good.  
Low speed gear like serial ports use old/slow USB.  There is about a 1/2 ms 
peak-to-peak of jitter.

There are several options for low cost units that require some soldering.  
The Garmin GPS-LVC-18x is popular.  Ahh.  This looks like a no-soldering 
option.  $105
  http://psn.quake.net/gps/gps18.html

My favorite at this time is the Sure demo board.  Poke SKG16A into eBay.  
It's under $40 from China.  If you would use one but don't have a soldering 
iron (or neighbor, friend, nephew...), I'm willing to wire up the PPS signal 
to the serial port on a few of them.  My eyes may not be good enough for the 
USB version.


There is another not-quite-low cost option that doesn't require any 
soldering.  You can get a Raspberry Pi with GPS hat and everything for a bit 
over $100.  I'll say more if anybody is interested.

I'll do the assembly and setup on a few if you don't like that stuff.  After 
that, you just SSH in.

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1) Several years ago, I went to a fun talk by the guy who designed the 
Roomba.  Part of their market research was to ask people how much they could 
spend on something without consulting their spouse/partner.  The answer was 
$200 which is how much the first ones cost.

-- 
These are my opinions.  I hate spam.