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

Terje Mathisen "terje.mathisen at tmsw.no" at ntp.org
Fri Apr 1 22:03:48 UTC 2011

Terje Mathisen wrote:
> unruh wrote:
>> On 2011-03-31, Terje Mathisen<"terje.mathisen at tmsw.no"> wrote:
>>> Based on this I tried to use HyperTrm to send the pdf sample command to
>>> turn on WAAS capability:
>> I think WAAS is turned on by default. My sure lists that it is using
>> DGPS but no DGPS station ID or time since source. It gives about a 1.5m
>> standard deviation error, which is what you get with WAAS.
> Probably not: It does report which sats it is currently tracking and I
> have not seen any EGNOS sats listed.
>>> $PMTK513,1*28<CR><LF>
>>> but it didn't seem to work. It is possible that the EOL sequence needs
>>> to be transmitted without any time gap, so I'll write tiny program to
>>> send custom commands.
>> Use minicom with the Y command to send a file. On garmin they do not
>> care that the checksum is sent.
> OK, I've realized that HyperTrm can also send files.
> OTOH, my first serious piece of programming ever was a terminal emulator
> and file transfer program, so hacking together a q&d NMEA sender would
> be fun.

I've done some more careful inspection of the Sure GPS comms trace:

It really looks like the GPS does _not_ listen to commands by default, 
instead the controlling program sends a solitary '0' char to ask for 
"permission to talk".

About 200 ms later the GPS boards drop the CD (Carrier Detect) line, and 
then the gps.exe program sends the private NMEA message.

As soon as the ending <CR><LF> arrives the GPS turns CD back on and 
restarts the configured NMEA messages.

If this sequence is required by default, then it must also be possible 
to turn off such very non-standard GPS behavior, right?


- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

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