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functions

 
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Guest
functions
PostPosted: Tue Mar 02, 2010 3:40 am     Reply with quote
hi there,

i have a code which get data from a rs232 gps devices in side it's own function, this all works fine.

Code:

void get_gps(){
do{
   cget = fgetc(GPS);
 fprintf(PC,"%s\n",cget);
}}


but i have another code in the main, which has a constant while loop:

Code:

main() {
 while (True)
  {
(if statements); - this is the other code
void get_gps();
delay_ms(500);
}
}


only thing that works is the void get_gps(); the if statements in the while loop doesnt work.

i there a way of making both work with out using a interrupt?

thanks

Jonny b
Eddy71ua



Joined: 23 Sep 2009
Posts: 55
Location: Ukraine

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Re: functions
PostPosted: Tue Mar 02, 2010 3:47 am     Reply with quote
Anonymous wrote:
hi there,

Code:

main() {
 while (True)
  {
(if statements); - this is the other code
get_gps();
delay_ms(500);
}
}




Try this code Smile
Wayne_



Joined: 10 Oct 2007
Posts: 681

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PostPosted: Tue Mar 02, 2010 4:00 am     Reply with quote
Code:

void get_gps(){
  do{
     cget = fgetc(GPS);
     fprintf(PC,"%s\n",cget);
  }
}


This also has an infinite loop in it. Once you enter this routine it WILL NOT exit. Actually it will probably not compile without the while statement!

You can fix this several ways and it all depends on what else your code is doing.

If you know how much data you will receive :-
Code:

void get_gps(){
  int i = 10; // Receive 10 chars
  for (; i > 0; i--)
  {
    cget = fgetc(GPS);
    fprintf(PC,"%s\n",cget);
  }
}

I would not use this, if you miss a char or the number of chars is different to what you expect your code will either wait indefinitely or get out of sync.

If you know what the termination char is for your data (usually '\r' or '\n') for modems then keep reading until you get this.

Code:

void get_gps(){
  do{
     cget = fgetc(GPS);
     fprintf(PC,"%s\n",cget);
  } while (cget != '\r');
}


or just use gets instead:-
Code:

void get_gps(){
     cget = fgets(GPS);
     fprintf(PC,"%s\n",cget);
}


What is cget defined as ?
Your printf is expecting a string but you use fgetc to read a single char!

Last edited by Wayne_ on Tue Mar 02, 2010 4:02 am; edited 1 time in total
Ttelmah
Guest
PostPosted: Tue Mar 02, 2010 4:02 am     Reply with quote
A number of separate problems:
First, if you do get to the outside loop, because of the long delay (500mSec), you _will_ miss RS232 data, and possibly hang the UART....
Second, the get_gps function, will sit _waiting_ for data to arrive from the GPS. While doing so, nothing in the external loop will be executed...
Now, whether this can be done without interrupts, depends on how long the 'if' statements will take. If the total is more than one character time, you will risk missing serial data. But the basic approach would need to be something like:
Code:

#define LOOPSPERTEST (255)
main() {
  int8 loopcount=LOOPSPERTEST;
  while (True)  {
    if (loopcount) --loopcount;
    else {
       loopcount=LOOPSPERTEST;
       //other code here;
       }
    get_gps();
    }
}

//You adjust 'LOOPSPERTEST' to adjust how frequently the 'other code'
//is executed

void get_gps(void) {
   if (kbhit(GPS)) {
      cget = fgetc(GPS); //Only read the GPS if a character is waiting
      fprintf(PC,"%c",cget);
   }
}


There is another problem in your code, which actually suggests that 'get_gps', is _not_ working. 'cget', is a character, not a string. When you print it as a string, the code will print everything from memory, till it happens to hit a '\0' character.
The void declaration in calling the funstion from main, is redundant.
The GPS stream, needs to be using a hardware UART, for this to work.

Best Wishes
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