[ts-7000] Re: Help connecting to GPS on com2

["Phil" <>]

Hi Rob,

Apart from any issues that you may have with "getty" processes 
running on the COM that you are trying to talk to the GPS with, 
there are problems with your code.



In the function below...

> int read_port(int file_id)
> {
>       char            buffer[512];
>       int             count=0;
>       int             lines = 0;
>       
>       while(lines < 50)
>       {
>               read(file_id, buffer, count);
>               lines++;
>               /* Add terminator and print if non-zero */
>               if(count > 0)
>               {
>                       buffer[count] = '\0';
>                       printf("Line %d has %d characters\n", lines, 
count);
>                       printf("%s\n", buffer);
>               }
>               else
>               {
>                       printf("Zero characters read\n");
>               }
>       }
> }

You are using the "read()" function incorrectly. What you would 
probably be after is more this...
>               count = read(file_id, buffer, 512);

In your code you were actually asking for 0 (the value in 'count') 
bytes to be read from the com port so that was what it was giving 
you. Plus the value in count would never have changed anyway, 
because that 3rd parameter to read() is just an input.



Also, you probably need to make some changes to your port 
initialisation code below...

> void port_configuration(int file_id)
> {
>       struct termios options;
>       int            x;
>       
>       tcgetattr (file_id, &options);
>       printf("speed in %d out %d\n", options.c_ispeed, 
options.c_ospeed);
>       printf("mode in %d out %d\n", options.c_iflag, 
options.c_oflag);
>       printf("control flag %d\n", options.c_cflag);
>       printf("local flag %d\n", options.c_lflag);
>       
>       cfsetispeed(&options, B4800);
>       cfsetospeed(&options, B4800);
>       options.c_cflag = 2096;
>       options.c_lflag = 4;
>       options.c_oflag = 0;
>       options.c_cflag |= (CLOCAL | CREAD);
>       options.c_cflag &= ~PARENB;
>       options.c_cflag &= ~CSTOPB;
>       options.c_cflag &= ~CSIZE;
>       options.c_cflag |= CS8; 
>       options.c_cflag &= ~CRTSCTS;
>       tcsetattr (file_id, TCSANOW, &options);
> }

Most implementations, including the TS boards as far as I know, 
store the baud rate setting in the 'cflag' member. So in your code 
above, the baud rate setting gets wiped straight away by setting 
cflag. Also, with setting the flags to values (like 2096 and 4) and 
then doing & and | operations makes it a bit hard to understand. And 
it appears that the port would be in 'non-canonical' mode, which 
means you wont get the input in a line-by-line form. Maybe try 
something like the following.

>       options.c_cflag = CLOCAL | CREAD | CS8;
>       options.c_lflag = ICANON;
>       options.c_iflag = 0;
>       options.c_oflag = 0;
>       cfsetispeed(&options, B4800);
>       cfsetospeed(&options, B4800);
>       tcsetattr (file_id, TCSANOW, &options);

Depending on the actual output of the GPS (eg. whether it terminates 
lines with CR or LF) you may need to adjust the above or some other 
members of the termios structure.

Google for 'man termios' (if you haven't already) for information on 
the above functions and structures.

Hope this helps!!

Cheers
Phil






 
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