Example

A simple example illustrates placing data in the extended memory, reading a data from the extended memory and storing the data address to a linear pointer.

Listing: Placing Data in the Linear Memory



...
#include <mmu_lda.h>

#pragma CONST_SEG __LINEAR_SEG DATA_LINEAR

const int x=2;

#pragma CONST_SEG DEFAULT

int y;

void f() { 

  /* y = x; */

  __LOAD_LAP_ADDRESS(x);

  __LOAD_WORD_INC(y);

}

In PRM file, place segment DATA_LINEAR at the correct address.

Note: Objects that are accessed using linear addressing can still be placed in paged segments, but this addressing should be used when objects (for example. variables, arrays) span multiple pages.

Note: Make sure not to define the same memory area both as paged and linear.

  //PRM file

  SEGMENTS

...

  //PPAGE_5     =  READ_ONLY    0x058000 TO 0x05BFFF;

...

  ROM_LINEAR  =  READ_ONLY    0x014000'F TO 0x017FFF'F

...

END

  PLACEMENT

...

  DEFAULT_ROM, PAGED_ROM

     INTO PPAGE_0,PPAGE_2,PPAGE_4,/*PPAGE_5,*/
  PPAGE_6,PPAGE_7,ROM1;

...

  DATA_LINEAR     INTO    ROM_LINEAR;

...

END

Note: When use linear address, a single quote ' (in C '\'') character and a F ('F') character should be added to the end of address to let the linker know it is a linear reference.