topic Re: far to near pointer conversion. (MC9S12DP512) in S12 / MagniV Microcontrollers

far to near pointer conversion. (MC9S12DP512)

ssinfod — Wed, 18 Oct 2006 20:41:02 GMT

Hi,

I want to display a char[] from a banked page without using the -CpPPAGE=RUNTIME compiler option.

I think I can use the lower 2 bytes of the address of the char[] since I will display the data from the same page.

So my goal is to convert a char *far to a char *near.

*far is on 3 bytes : Page, High address, Low address

*near is on 2 byers : High address, Low address.

The code below works but I have a compiler warning. What is exact way to convert a *far to a *near without a compiler warning.

Note : The data and the code are in page 3D.

Thanks..

#pragma CONST_SEG __PPAGE_SEG BANKED_DATA_3D

static const char my_string[] = "This is a string"; // Located in page 3D

#pragma CODE_SEG ROM_3D
#pragma CONST_SEG CONST_3D

void far_pstr(const sc *far ptr)
{
while (*ptr) { putchar(*ptr++); }
}

void near_pstr(const sc *ptr)
{
while (*ptr) { putchar(*ptr++); }
}

void print_test(void)

{

char *ptr = my_string; // This gives : Warning : C1860: Pointer conversion: possible loss of data

char *near ptr2 = (char *near) my_string; // This gives : Warning : C1860: Pointer conversion: possible loss of data

near_pstr(my_string); // This gives : Warning : C1860: Pointer conversion: possible loss of data

far_pstr(my_string); // This gives : Warning : C12002: Use DPAGE, PPAGE, EPAGE to specify the page register. Assumed DPAGE

}

Re: far to near pointer conversion. (MC9S12DP512)

ssinfod — Wed, 18 Oct 2006 21:53:46 GMT

FYI,

I found this solution...

  char* temp;
   asm
   {
       LDD   #my_string
       STD   temp
   }
   pstr(temp);

Re: far to near pointer conversion. (MC9S12DP512)

CompilerGuru — Thu, 19 Oct 2006 03:04:19 GMT

You could:
- not tell the compiler that those constants are far.
- use a cast to int, probably hidden by some macro (#define TO_16_BIT_CHAR_PTR(x) ((const char*)(int)(x))

The compiler on its own does not know that the code and the constants end up at the same page,
so by default the warning is justified.

Daniel

#pragma CONST_SEG __PPAGE_SEG BANKED_DATA_3D                                  
static const char my_string[] = "This is a string";                         // Located in page 3D
#pragma CONST_SEG BANKED_DATA_3D_TOO
static const char another_my_string[] = "This is a string";                 // Located in page 3D

#pragma CODE_SEG ROM_3D

void putchar(char s) {
  s++;
}

void near_pstr(const char* ptr) {
   while (*ptr) { putchar(*ptr++); }
}
void t(void) {
  near_pstr((char*)(int)my_string);
  near_pstr(another_my_string);
}

Re: far to near pointer conversion. (MC9S12DP512)

ssinfod — Fri, 20 Oct 2006 07:54:00 GMT

Thanks, your solution works fine