[Xastir] HSP Problem

[Stephen West-Fisher]

Stephen West-Fisher wrote:
> There are two problems, but I haven't come up with a fix yet. The minor 
> one is that you are correct, timings are a problem. I have found that 
> setting the GPS timing at 20 seconds will cause DTR to switch back and 
> forth, but 60 seconds will hold DTR low all the time.
> 
> Now for the major problem, I'm trying to come up with something that 
> will work for me until you can properly correct it. The problem is in
> interface.c in channel_data:
>         switch(port_data[port].device_type) {
> 
>             case DEVICE_SERIAL_GPS:
>             case DEVICE_SERIAL_TNC_HSP_GPS:
>             case DEVICE_NET_GPSD:
> 
>                 // One of the three types of interfaces that might
>                 // send in a lot of GPS data constantly.  Save only
>                 // GPRMC and GPGGA strings into global variables.
>                 // Drop other GPS strings on the floor.
>                 //
>                 if ( (length > 7) && (strncmp(string,"$GPRMC,",7) == 0) ) {
>                     strncpy(gprmc_save_string,string,MAX_LINE_SIZE);
>                     gps_port_save = port;
>                 }
>                 else if ( (length > 7) && (strncmp(string,"$GPGGA,",7) 
> == 0) ) {
>                     strncpy(gpgga_save_string,string,MAX_LINE_SIZE);
>                     gps_port_save = port;
>                 }
>                 else {  // Else drop the string on the floor.
>                 }
>                 break;
> // We need to make sure that the variables stating that a string is
> // available are reset in any case.  Look at how/where data_avail is
> // reset.  We may not care if we just wait for data_avail to be
> // cleared before writing to the string again.
> 
>             default:    // Not one of the above three types, decode
>                         // the string normally.
>                 incoming_data = string;
>                 incoming_data_length = length;
>                 data_port = port;
>                 data_avail = 1;
>                 //fprintf(stderr,"data_avail\n");
>                 break;
>         }
> 
> Since DEVICE_SERIAL_TNC_HSP_GPS is true, all data is considered GPS 
> data. So the needed GPS strings are OK, but all other data received on 
> the port goes into the bit bucket, including received packets!
> 
> Packets are never moved to incomming_data and data_avail is never true, 
> so they are never parsed in main.c.
My quick and dirty solution, which also speeds up getting the valid GPS fix:
         switch(port_data[port].device_type) {

             case DEVICE_SERIAL_GPS:
             case DEVICE_NET_GPSD:

                 // One of the three types of interfaces that might
                 // send in a lot of GPS data constantly.  Save only
                 // GPRMC and GPGGA strings into global variables.
                 // Drop other GPS strings on the floor.
                 //
                 if ( (length > 7) && (strncmp(string,"$GPRMC,",7) == 0) ) {
                     strncpy(gprmc_save_string,string,MAX_LINE_SIZE);
                     gps_port_save = port;
                 }
                 else if ( (length > 7) && (strncmp(string,"$GPGGA,",7) 
== 0) ) {
                     strncpy(gpgga_save_string,string,MAX_LINE_SIZE);
                     gps_port_save = port;
                 }
                 else {  // Else drop the string on the floor.
                 }
                 break;
	case DEVICE_SERIAL_TNC_HSP_GPS:

                 // One of the three types of interfaces that might
                 // send in a lot of GPS data constantly.  Save only
                 // GPRMC and GPGGA strings into global variables.
                 // Drop other GPS strings on the floor.
                 //
	  if ((length > 3) && (strncmp(string,"$GP",3) == 0)) {
                 if ( (length > 7) && (strncmp(string,"$GPRMC,",7) == 0) ) {
                     strncpy(gprmc_save_string,string,MAX_LINE_SIZE);
                     gps_port_save = port;
                 }
                 else if ( (length > 7) && (strncmp(string,"$GPGGA,",7) 
== 0) ) {
                     strncpy(gpgga_save_string,string,MAX_LINE_SIZE);
                     gps_port_save = port;
                 }
                 else {  // Else drop the string on the floor.
                 }
	  }

// We need to make sure that the variables stating that a string is
// available are reset in any case.  Look at how/where data_avail is
// reset.  We may not care if we just wait for data_avail to be
// cleared before writing to the string again.

             default:    // Not one of the above three types, decode
                         // the string normally.
                 incoming_data = string;
                 incoming_data_length = length;
                 data_port = port;
                 data_avail = 1;
                 //fprintf(stderr,"data_avail\n");
                 break;
         }

I'm sure some developer who knows more about the GPS strings can do a 
better job :-) I tried to just add the additional if statment to the 
previous code, but I couldn't get the break to do what I want. The 
system kept trying to parse invalid strings. It's been a number of years 
since I did much work in C.

-- 
Stephen West-Fisher
Coastal Data Systems
727.418.9774
http://www.coastaldatasystems.com/