[time] GPS sensor for time synchronization

Hal Murray hmurray
Thu Jun 1 08:06:41 UTC 2006


> I'm wondering if anybody on this list can suggest any commercial GPS
> sensor that can meet the following requirement

> - waterproof
> - support linux
> - support ntp
> - usb interface (the serialport on our router board has been
>      used for other purpose)
> - have at least 1ms accuracy (it will be great if it supports PPS)
> - can be use in Australia 

I don't think you will get good GPS timing over USB.  I've never heard of any 
success stories.

They make inexpensive serial to USB adapters.  Can you run your current 
serial port over one of them to free up the real serial port?

You might be able to feed the PPS signal in via the printer port.  I don't 
know of any Linux support for that.  It shouldn't be too hard to add if you 
copy the PPS-over-serial code. (That assumes you have somebody good at kernel 
hacking.)


> I saw something from deluo. But not sure how would it support the 1us
> accuracy they claim. Does anybody here happen to have any experience
> with this device?

That web page didn't mention PPS or anything timing related, so I doubt if 
you will get good timing from it.  It seems reasonable for the unit to know 
the time internally to 1 usec, but without a few more words I don't see how 
they are planning to pass that on to your system.


One of the GPS manufacturers has a backwards PPS type signaling.  You flap a 
signal and it tells you when it saw the transition.  You could use that by 
flapping a printer port bit.  That might let you get the serial connection 
over a serial to USB adapter.  Unfortunately, I don't remember who does that. 
 You can probably find it with a linear search of documentation for the 
drivers in the NTP package.


You might get more ideas on comp.protocols.time.ntp (usenet) and/or at 
http://ntp.isc.org/



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