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Re: Getting timeout error while reading data.

From: Gary E. Miller
Subject: Re: Getting timeout error while reading data.
Date: Fri, 15 Jul 2022 10:06:59 -0700

Yo Bhavna!

On Fri, 15 Jul 2022 11:50:31 +0530
Bhavna Harani <> wrote:

> I am giving data dynamically to gpsd over udp by the below command.
> gpsd -D 1 -n udp://

You skipped over some important lot of details.  What version of gpsd?  What is
the source for "udp://"

> every 1 second I am feeding data to udp socket.

How?  What sort of data?

> When I tried to read
> the data
> using gpslib I got a timeout error.

Getting way ahead of yourself.  Don't bother to touch libgps until
 the "-D 4" log from gpsd looks good.  Then move on to cgps, befoure
looking at libgps.

> Below is a snippet to feed data at 1 second frequency.
> while(fgets(buffer, bufferLength, filePointer))
> {
>     printf("%s\n", buffer);
>     sleep(1);
> sendto(sockfd, buffer, strlen(buffer),MSG_CONFIRM, (const struct
> sockaddr *) &servaddr,sizeof(servaddr));
> }

Way too small a snippet.  Also, never use strlen(), use strnlen()

> Below is a snippet for reading the data.

Way to small a snippet, and very premature.  Look at the -D4" first,
then cgps, then libgps.

> if (0 != gps_open("localhost", "2947", &gpsd_gps_data))
> {
> printf( "LC79D_GNSS open error");
> exit(-1);
> }
> /*enable watch enable from gpsd demon*/
> (void)gps_stream(&gpsd_gps_data, WATCH_ENABLE | WATCH_JSON, NULL);

Failed to check the return code.

> // Wait for data available.
> #define GNSS_DATA_TIME_OUT  5000000
> while (gps_waiting(&gpsd_gps_data, GNSS_DATA_TIME_OUT))
> {
> if (-1 == gps_read(&gpsd_gps_data, NULL, 0))
> {printf ( "GNSS Read ERROR");
> ....
> }
> printf ( "timeout");
> }

Might work, can;t tell without working code.  No ouput that ever says
you got data...

>  I have tried with "gpspipe -r" ,I was able to get a raw string which
> I parsed dynamically.

Your C code asks for JSON, but you compare to psuedo NMEA.  Apples and

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

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