Em 5/11/2011 20:36, Harold Hallikainen escreveu:
> I'm mostly doing PIC32 stuff now with C32, the linker, etc. I do a little
> assembly for it, but very little. I find linker scripts very cryptic. It'=
d
> sure be nice if they were commented a bit more. It'd also be nice to
> easily define the address where a function is to be placed. The new
> version of C32 has an attribute that allows this, but it appears there ar=
e
> various issues with this new version (especially in printf).
>
> In my bootloader, I'd like to have a jump table at a specific address tha=
t
> does not move as I make code changes. I see how I could do it in assembly
> (including use of org, which, it appears, is based on the section start,
> not the absolute address), but it'd be nice to be able to do it in C.
> Something like:
>
> org SomeAbsoluteVirtualAddress
> function1: goto LocalFunction1;
> Function2: goto LocalFunction2;
> Function3: goto LocalFunction3;
>
> The "LocalFunctions" would still do all the stack operations (getting
> parameters, allocating local variables, cleaning up the stack, etc.). The
> jump table would just provide a fixed address to access the function.
>
> I did this on the PIC24, building my own interrupt jump table since the
> PIC24 places the interrupt vector table in the boot section. I just had
> all those original interrupt vectors point into my jump table, which then
> pointed to the actual interrupt function. I THINK I did it in C (I'll hav=
e
> to look at the code), but MAY have done it in assembly.
>
> I tried the above stuff (
> function1: goto LocalFunction1;
> Function2: goto LocalFunction2;
> Function3: goto LocalFunction3;
> ), but the C32 compiler did not like it. I don't think it liked the label=
s
> (expecting a return value type instead). For now, I've put functions that
> call local functions at the top of the section, but that uses more stack
> space and is pretty inefficient.
>
> So... how do I do a jump table in C32? Or do I go back to assembly?
>
> THANKS!
>
> Harold


First, you have to deal with linker-scripts to be able to put your jump
table at the fixed and predefined position, creating a named section
with 'protected' attribute.
Then you have to use function-pointers, which is the C way of calling
functions by pointer.

Example:
int (*fp1)( int a, int b, int c );    // fp1 is a function-pointer
variable that may point to a function returning int and taking 3 ints as
arguments.
void (*fp2)( void );    // fp2 is a function-pointer that points to a
function returning void and taking no arguments.

fp1 =3D LocalFunction1;    // Please not the lack of parenthesis and
arguments. You are taking the address of the function.
fp2 =3D LocalFunction2;

x =3D fp1( 1, 2, 3 );
fp2();

fp1 =3D LocalFunction3;
y =3D fp1( 4, 5, 6 );


ALTERNATIVE ( build-time table creation):


typedef int (*functionpointer_t)( int a, int b, int c );

functionpointer_t    FunctionTable[NUMBER_OF_ENTRIES] =3D { lf1, lf2, lf3,
.... };

x =3D FunctionTable[i]( a, b, c );    // Call function number 'i' with
arguments 'a', 'b', 'c'.


Best regards,

Isaac

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