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Char Stars not passing to functions

 
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jmann



Joined: 27 Dec 2004
Posts: 21

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Char Stars not passing to functions
PostPosted: Wed Apr 13, 2005 7:01 pm     Reply with quote
I cannot get a variable to pass to a function as a pointer.

for example, I call:
Code:
JeffSend(SomeString, 100);

in which the function is:
Code:
int16 JeffSend(char *data, int16 len)
{
//some code
}


but in the function, data is 0x0000, it is not the location of SomeString

Any idea why? SomeString is a gobally decleared array of char, i.e.: a string (and is not a constant).
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Wed Apr 13, 2005 7:30 pm     Reply with quote
This has always worked, so likely the problem is in your code. There are several things that can be wrong therefor please post a small but complete working program showing your problem.

Also mention the compiler version you are using.
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Thu Apr 14, 2005 1:06 pm     Reply with quote
Here is a test program that shows how to do it. This was tested with
PCM vs. 3.222. The output on the terminal window is:

Hello World
Code:

#include <16F877.H>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

void display_string(char *ptr)
{
printf("%s", ptr);
}

//===================
void main()
{
char array[20];

strcpy(array, "Hello World \n\r");
display_string(array);

while(1);
}
jmann



Joined: 27 Dec 2004
Posts: 21

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PostPosted: Fri Apr 15, 2005 4:09 am     Reply with quote
when send-in calls writenetwork, data should have the value of 0x015F (the location of wr_ptr), however it gets the value 0x0020.

compiler Version 3.207 target chip 18F452

(also, I know that endian is reversed between the two devices I am trying to use, so void endian(int32) reverses endian after and before writing, but that is not important to this problem)


Code:
//-----------------------------------
//Preform a sequential write
//-----------------------------------
int1 WriteNetwork(int16 Addr, char* Data, int16 len)
{
   int16 i;
   char Err = NOERROR;

   I2CInterrupts(DisableI2C);// Disable Interrupt
   i2c_start();            // START Signal Of Address
   if(i2c_write(W3100Awrite)==NoError   &&
      i2c_write(make8(addr,1))==NoError && //address MSD
      i2c_write(make8(addr,0))==NoError )  //address LSD
   {
      for(i = 0 ; i < len ; i++)
         if(i2c_Write(*Data++)==ERROR)
         {
            err=ERROR;
            break;
         }
   }
   else //error occured
   {
      err=ERROR;
   }
   i2c_stop();                   // STOP Signal Of Address
   I2CInterrupts(EnableI2C);// Enable Interrupt
   return Err;
}

Code:
int16 send_in(char* data, int16 len)
{
   char k;
   signed int16 size;
   int32 wr_ptr, ack_ptr;
   int16 address;

S_START:
//   I2CInterrupts(DisableI2C);

   ReadNetwork(SHADOW_TXWR_PTR(0), wr_ptr, 3);   // Must read the shadow register for reading 4byte pointer registers
   delay_us(2);                    // wait for reading 4byte pointer registers safely
   ReadNetwork(TX_WR_PTR(0), wr_ptr, 4);
   endian(wr_ptr);

   ReadNetwork(SHADOW_TXACK_PTR(0), ack_ptr, 3);  // Must read the shadow register for reading 4byte pointer registers
   delay_us(2);                    // wait for reading 4byte pointer registers safely
   ReadNetwork(TX_ACK_PTR(0), ack_ptr, 4);
   endian(ack_ptr);

//   I2CInterrupts(EnableI2C);

   // Calculate send free buffer size
   if ((wr_ptr&SMASK) >= (ack_ptr&SMASK))
      size = SSIZE - ((wr_ptr&SMASK) - (ack_ptr&SMASK));
   else
      size = SSIZE - (0 - (ack_ptr&SMASK) + (wr_ptr&SMASK));

   if (size > SSIZE)                                                            // Recalulate after some delay because of error in pointer caluation
   {
      if (ReadNetworkRegister(SOCK_STATUS(0)) != SOCK_ESTABLISHED) return 0;              // Error

      delay_ms(1);

      goto S_START;
   }

   if (size == 0)                                                                  // Wait when previous sending has not finished yet and there's no free buffer
   {
      if (ReadNetworkRegister(SOCK_STATUS(0)) != SOCK_ESTABLISHED) return 0;              // Error
      delay_ms(1);
      goto S_START;
   }
   else if (size < len)   len = size;

   address = (int16)( SEND_DATA_BUF + ((int16)(wr_ptr)) & SMASK);    // Calculate pointer to data copy
   WriteNetwork(address, data, len);                                               // data copy

   while (WriteNetworkRegister(COMMAND(0), CSEND))                                       // Confirm send command
      if (ReadNetworkRegister(SOCK_STATUS(0)) != SOCK_ESTABLISHED) return 0;              // Error

   wr_ptr = wr_ptr + len;   
   endian( wr_ptr);                                            // tx_wr_ptr update
   WriteNetwork(TX_WR_PTR(0), wr_ptr, 4);

   WriteNetworkRegister(COMMAND(0),CSEND);                                               // SEND

    return   (len);
}
Mark



Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA

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PostPosted: Fri Apr 15, 2005 6:12 am     Reply with quote
Take a look at these three statements. Data is defined as a pointer to a char. wr_ptr is defined as int32 and you are not even calling the function with the address of wr_ptr but using the value. I can see why you are having problems.
Code:

int1 WriteNetwork(int16 Addr, char* Data, int16 len)
int32 wr_ptr, ack_ptr;
WriteNetwork(TX_WR_PTR(0), wr_ptr, 4);
jmann



Joined: 27 Dec 2004
Posts: 21

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PostPosted: Sat Apr 16, 2005 9:27 am     Reply with quote
but a pointer is a pointer, right?

then wouild this work?:

Code:
int16 send_in(char* data, int16 len)
{
   char k;
   signed int16 size;
   int32 wr_ptr, ack_ptr;
   int16 address;
   char* pointer;

   pointer = (&wr_ptr);                                   //make pointer point to the location of wr_ptr
   WriteNetwork(TX_WR_PTR(0), pointer, 4); //now call function with a pointer pointing of the same type



I know it is little endian, and would have to deal with that.
Mark



Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA

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PostPosted: Sat Apr 16, 2005 12:35 pm     Reply with quote
All you need is
Code:

WriteNetwork(TX_WR_PTR(0), &wr_ptr, 4);


but
Code:

WriteNetwork(TX_WR_PTR(0), (char*)&wr_ptr, 4);
is more correct
Guest
PostPosted: Sat Apr 16, 2005 4:04 pm     Reply with quote
thank you, I am making those changes.
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