[ntp:questions] Re. Sure GPS - PPS not working

Richard Steedman richard.steedman at btinternet.com
Fri Jan 23 20:09:35 UTC 2015

Back in Dec 2013, Chris North wrote:

>I have managed to fix it, and it was a bit unexpected. When I first 
>installed the Sure, I used a USB connection and got it working OK. I then 
>used a Serial-USB adapter and was pleased to find that it passed DCD and 
>that PPS was working. The jitter was rather high, though - about 0.3 mS. I 
>bought a 2-port serial PCI card and a serial cable, and immediately had a 
>massive improvement in performance. Recently, however, I found that PPS had

>stopped working, as you have seen above.
>What I think happened was this: when I plugged in the new card it used the 
>standard Windows serial.sys, which I replaced with serialpps.sys. Now this 
>card is part of a range of multifunction cards that offer various I/O 
>interfaces. At some time Windows Update probably found the manufacturer's 
>drivers and installed them (automatically, or as an option that I just 
>accepted). The new driver ignores serial.sys and has its own software. So I

>poked around in the registry and changed the ImagePath for one of the
>new services to point to serialpps.sys. This seems to have fixed it. As I 
>don't use the COMn ports for anything else, I won't worry about possible 

I am trying to get PPS working with a Sure GPS board connected to a laptop
running Win7.  I'm not getting very far and I'm guessing it's because
neither of the interface options available to me use the serial.sys driver:
- Direct connection of the Sure's USB port to the laptop means using the
  Silicon Labs 2102 chip on the Sure board and it uses drivers called
  silabenm.sys and silabser.sys
- Connecting the Sure board's RS-232 output to the laptop via a Prolific
  USB to serial adaptor means using the Prolific driver ser2pl.sys

Chris, if you still follow this listserv, could you tell me which
serial-to-USB adaptor you were using which successfully passed PPS to ntp?
I am not expecting the jitter to be any better than of the order of 1ms
since the USB interface samples the DCD line at 1024Hz but would still like
to try to get my setup working.

Thanks, Richard.

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