Linking with Variables in Program Memory

The compiler creates special sections in the output file for variables in program memory.

This is a description of all data in program memory sections:

.data.pmem (initialized program memory data)
.const.data.pmem (constant program memory data)
bss.pmem (uninitialized program memory data)

The following sections are also generated if you choose to generate separate sections for char data:

.data.char.pmem (initialized program memory chars)
.const.data.char.pmem (constant program memory chars)
.bss.char.pmem (uninitialized program memory chars)

These sections are used in the linker command file just like normal sections. A typical linker command file for a program that uses data in program memory looks like the following listing

Note: __pmem qualifier can be used only for global variable and is not available for local variable.

Listing: Typical Linker Command File

MEMORY

{

    .p_RAM              (RWX) : ORIGIN = 0x0082,   LENGTH = 0xFF3E

    .p_reserved_regs    (RWX) : ORIGIN = 0xFFC0,   LENGTH = 0x003F

    .p_RAM2             (RWX) : ORIGIN = 0xFFFF,   LENGTH = 0x0000

    .x_RAM              (RW)  : ORIGIN = 0x0001,   LENGTH = 0x7FFE   # SDM xRAM limit is 0x7FFF

}

SECTIONS

{

    .application_code :

    {v        # .text sections



        * (.text)

        * (rtlib.text)

        * (fp_engine.text)

        * (user.text)

        * (.data.pmem)            # program memory initalized data

        * (.const.data.pmem)      # program memory constant data

        * (.bss.pmem)             # program memory uninitialized data

    } > .p_RAM



    .data :

    {

        # .data sections



        * (.const.data.char)  # used if "Emit Separate Char Data Section" enabled

        * (.const.data)v        * (fp_state.data)

        * (rtlib.data)

        * (.data.char)        # used if "Emit Separate Char Data Section" enabled

        * (.data)



        # .bss sections



        * (rtlib.bss.lo)

        * (rtlib.bss)

        . = ALIGN(1);

        _START_BSS = .;

        * (.bss.char)         # used if "Emit Separate Char Data Section" enabled

        * (.bss)

        _END_BSS   = .;



        # setup the heap address



        . = ALIGN(4);

        _HEAP_ADDR = .;

        _HEAP_SIZE = 0x100;

        _HEAP_END = _HEAP_ADDR + _HEAP_SIZE;

        . = _HEAP_END;



        # setup the stack address



        _min_stack_size = 0x200;

        _stack_addr = _HEAP_END;

        _stack_end  = _stack_addr + _min_stack_size;

        . = _stack_end;



        # export heap and stack runtime to libraries



        F_heap_addr   = _HEAP_ADDR;

        F_heap_end    = _HEAP_END;

        F_Lstack_addr = _HEAP_END;

        F_start_bss   = _START_BSS;

        F_end_bss     = _END_BSS;

    } > .x_RAM

}