topic Why can't I allocate an array of function pointers into FLASH? in 8-bit Microcontrollers

Why can't I allocate an array of function pointers into FLASH?

wre — Sat, 15 Apr 2006 02:09:13 GMT

Hi, using CodWarrior 3.1 for HC(S)08, I am trying to get an array of function pointers allocated into FLASH (.rodata). Instead they are allocated into RAM (.data) and initialization code loads the array.

Here is what I am doing:

const void (*sapfnIPHandlers [])(void) =

{

func1,

func2,

func3,

...

funcn

}

void func1 (void)

{

...

}

etc.

I have tried the -Cc compiler option with no change in the output.

This code is simply a way of parsing some commands to get to the right function. What am I doing wrong (or what is the compiler doing wrong)?

Thanks

Re: Why can't I allocate an array of function pointers into FLASH?

tequila — Sat, 15 Apr 2006 03:09:18 GMT

Function pointers are normally stored in RAM, here is a workaround:

const unsigned int pFunction[]={(unsigned int)&SafePoint,(unsigned int)&BlackButton};

and you call it this way:

((void (*)(void))pFunction[0])();

Cheers

Re: Why can't I allocate an array of function pointers into FLASH?

CompilerGuru — Sat, 15 Apr 2006 07:40:22 GMT

The reason why the array ends up in RAM is a common error in C programming.
For pointers (including function pointers), qualifiers have to be after the *, hence this array:
>const void (*sapfnIPHandlers [2])(void);
if not constant. You can assign to it, try

>void test(void) { sapfnIPHandlers[0]= fun; }

The correct version is:
>void (*const sapfnIPHandlers [2])(void)= {fun0, fun1};

Well this works, but it is a bit hard to read in my point of view.
So for functions, I would use a typedef instead:

>typedef void (*FunctionType)(void);
>const FunctionType sapfnIPHandlers[2]= {fun0, fun1};

Bye
Daniel

Re: Why can't I allocate an array of function pointers into FLASH?

wre — Tue, 18 Apr 2006 22:42:40 GMT

Many thanks for both responses. The first one got me going without using RAM and the second simplifies things...although I will have to study it a bit more to see what it is actually doing...

typedef void (*FunctionType)(void);

OK, I see that it matches an example from K&R such that it is creating the type FunctionType which is a pointer to a function with no arguments and returns nothing.

Thanks

Message Edited by wre on 04-18-200611:54 AM