[ntp:questions] Sure Electronics GPS board: Amazing performance. :-)

David J Taylor david-taylor at blueyonder.co.uk.invalid
Wed Mar 16 09:45:48 UTC 2011

"Terje Mathisen" <"terje.mathisen at tmsw.no"> wrote in message 
news:l4c158-21f.ln1 at ntp6.tmsw.no...
> Terje Mathisen wrote:
>> b) Since both the PPS and NMEA drivers have fudge flags to use a 
>> falling
>> instead of the default rising edge of the DCD signal, I can use the
>> first version of David's hack, i.e. from the official PPS header via 
>> the
>> free RS232 level driver (U6 - pin 11->14). This should avoid the need 
>> to
>> solder anything to U5 pin 8.
> This worked perfectly, my (Windows) ntp.conf has the following lines:
> # Sure Electronics GPS board: COM1, 18=(16+2)9600 baud GPGGA
> server mode 18 minpoll 4 maxpoll 4 iburst prefer
> # Enable PPS, enable falling edge (inverted PPS), disable kernel PPS,
> # 0 ms PPS offset -100 ms NMEA offset
> fudge flag1 1 flag2 1 flag3 0 time1 0.0 time2 0.100 refid 
> "SURE"
>> Terje
>> PS. I've sent off emails to SkyNet, manufactor of the SkyLab gps 
>> chipset
>> used, asking for documentation on how to manually determine both baud
>> rate and which NMEA sentences should be sent each second.
>> I got one test reply from admin at honestar.com, but no other response so 
>> far.
> Still no reply, but I discovered by accident that if you leave the GPS 
> board unplugged for some hours, it will revert to 9600 baud from 
> whatever other speed setting you had previously selected.(I ran mine at 
> 38400)
> I assume this also means that any command to turn on/off specific NMEA 
> messages must be repeated.
> Terje


I have discovered, rather to my surprise, that the NMEA driver by default 
uses the /last/ sent sentence, rather than the first, so telling the 
driver to use the $GPGGA sentence is critical as (at least on the Windows 
port), only the /first/ sentence is timestamped with the PPS edge time. 
This means that there is no need to alter any of the settings for the 
board, and it works "out-of-the-box" with just the simple wiring addition. 
As I use Dave Hart's serialPPS.sys 32-bit device driver for kernel-mode 
timestamps, and I have the correct PPS signal polarity, this is what I 
have for the configuration:

  server minpoll 4
  server minpoll 4 mode 18 prefer

I've updated my Web page about using this delightful board here:


I also found the "forgets settings after some hours" issue (which I didn't 
see on the first board), so it's fortunate that out-of-the-box settings 

I would be most interested in a copy of the programming manual should you 
get one.


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