Hi Isaac,

    Thanks for the ideas and for taking the time to elaborate.  If I =

can't implement them here (mainly because of the complexity of the =

microchip fat library with so many callable functions and concerns about =

fixed RAM allocations to make the two compatible), the concepts will =

come in handy later.

Tony

Isaac Marino Bavaresco wrote:
> 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
> __________________________________________________
> Fa=E7a liga=E7=F5es para outros computadores com o novo Yahoo! Messenger =

> http://br.beta.messenger.yahoo.com/ =

>
>   =

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