Tony Vandiver escreveu:
> I'm trying to write a custom bootstrap to load in my application code =

> from an SD card.  I want to call file I/O routines located in my =

> bootstrap from my application rather than duplicating the file I/O =

> library functions in the application because it represents about 10% of =

> my code space.  Typically when I compile, I compile and link everything =

> that pertains to a project at the same time, but in this instance, do I =

> need to reference an object file from the bootstrap compilation without =

> compiling it into the application project, and if so, how do I keep it =

> from being relocated by the linker without expressly setting the address =

> of each function?  I'll start reading the compiler reference material =

> now and see how long it will take me to start drooling.
>
> Thanks for the help,
>
> Tony
>   =


You could put a 'jump table' at a fixed location in your bootstrap's
program space, with each entry jumping to one routine that you may call
from your application.

The reason for the 'jump table' is to make the entry points fixed, even
if you change your bootstrap code.

Assuming you are using MPLAB C18 (other Cs may have a slightly different
syntax, but not much even for other MCUs).

In the bootstrap:

#pragma code JUMPTABLE =3D 0x1f000

void JumpTable( void )
    {
    _asm
    goto mount;
    goto remove;
    goto ...
    _endasm;
    }

#pragma code

In your application you call the functions this way:

typedef void (*func_type1)( void );   // Pointer to a function that take
void and return void;
typedef int (*func_type2)( const char rom * );   // Pointer to a
function that take a string and return int;
....

#define mount() ((func_type1)0x1f000)() /* mount entry point is at
0x1f000 */
#define remove(name) ((func_type2)0x1f004)(name) /* remove entry point
is at 0x1f004 */
....

void main( void )
    {
    mount();
    remove( "backup.bin" );
    }

Best regards,

Isaac
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