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Sanity Check: Pointers

 
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bkamen



Joined: 07 Jan 2004
Posts: 1615
Location: Central Illinois, USA

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Sanity Check: Pointers
PostPosted: Wed Sep 16, 2009 4:09 pm     Reply with quote
Ok, this isn't working and from so many other examples, I can't seem to fish out why (other than a bug)


I have a function:

Code:
unsigned int rx_fifo_access (unsigned int *mode, char *c, unsigned int channel=0, unsigned int len=1 ) {

and inside, I set c with:

Code:
c = uart_rx_fifo[channel].buffer[out];


I've run the debugger and see this is fetching and assigning c with the right value.

upon exit of the function, the value of C is not passed back.

I'm calling it like this:

Code:
rx_fifo_access(READ, c, addr);


(I've also tried rx_fifo_access(READ, &c, addr) )

where c is declared as unsigned int c;


Now, I've determined that it's because I'm set in the code to

#device *=16

when I debug I notice that my pointer switches from an 8bit char to a 16bit int and then just dies on the return.

If I make my passed parm a 16bit variable, then it works.

So is this a bug?

I'm using PCH 4.099
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PCM programmer



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Posts: 21708

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PostPosted: Wed Sep 16, 2009 4:22 pm     Reply with quote
Post a short, complete, compilable example program so we can test it.
bkamen



Joined: 07 Jan 2004
Posts: 1615
Location: Central Illinois, USA

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PostPosted: Wed Sep 16, 2009 4:37 pm     Reply with quote
Here's what I'm running it on.. .adjust to your own as you like except to stay in the 18F family (to keep using PCH)

Code:
#include <18F97J60.h>

#device *=16 ICD=TRUE

#use delay(clock=41666700)
#fuses H4_SW
#fuses NOWDT,NOPROTECT,NODEBUG,NOIESO,WDT32768
#fuses NOFCMEN   // change this eventually to FCMEN

#opt 10

#use rs232(UART1, STREAM=USER, baud=115200, ERRORS)


void pointer_test ( char * c ) {

     c = 32;

}

void main (void) {
  char c;

  pointer_test(c);
  fprintf(USER, "%c", c);


  while (1);

}


I'm feel I'm just not doing this right...
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Dazed and confused? I don't think so. Just "plain lost" will do. :D
bkamen



Joined: 07 Jan 2004
Posts: 1615
Location: Central Illinois, USA

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PostPosted: Wed Sep 16, 2009 4:55 pm     Reply with quote
Nevermind, I think I got it.


This works:
Code:

#include <18F97J60.h>

#device *=16

#use delay(clock=41666700)
#fuses H4_SW
#fuses NOWDT,NOPROTECT,NODEBUG,NOIESO,WDT32768
#fuses NOFCMEN   // change this eventually to FCMEN

#opt 10

#use rs232(UART1, STREAM=USER, baud=115200, ERRORS)


void pointer_test ( char *c ) {
   int x=0;

    *c = 32;
   x = 1;  // this is just so I can step through MPLAB's Debug mode.
}

void main (void) {
  char c=0;

  pointer_test(&c);
  fprintf(USER, "%c", c);


  while (1);

}


If you're not used to passing around pointers... and don't do it for a while... it gets messy.

-ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D
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