Embedded C - Too many arguments to function (pointer)

Question

I am trying to invoke the following macro in my .cpp file:

#define IAP_ROM_LOCATION                0x1FFF1FF1UL
#define IAP_EXECUTE_CMD(a, b)           ((void (*)())(IAP_ROM_LOCATION))(a, b)

However, when I call said function like so:

IAP_EXECUTE_CMD(0, 0);

I get an error saying too many arguments specified? How is this? I would appreciate any pointers.

Development environment is GCC for Cortex-M3.

Answer 1

For readability, define a signature for the function to be called:

typedef void signature_t(int, int);

Then you can cast your ROM location

#define IAP_EXECUTE_CMD(a, b)  ((signature_t*)IAP_ROM_LOCATION) ((a),(b))

and with a recent GCC (current version of GCC is 4.6) I would make that an inline function

static inline void iap_execute_cmd(int a, int b) {
    ((signature_t*)IAP_ROM_LOCATION) ((a),(b));
}

Answer 2

(void (*)())(IAP_ROM_LOCATION)

This part casts IAP_ROM_LOCATION to a pointer to a function that takes no arguments and returns nothing (void (*)()). Hence you get an error when you want to pass any arguments to that function.

Answer 3

You can also do it with macros only:

#define IAP_ROM_LOCATION        0x1FFF1FF1UL
#define IAP_FUNC_SIGNATURE      void (*)(int, int)
#define IAP_EXECUTE_CMD(a, b)   ((IAP_FUNC_SIGNATURE)(IAP_ROM_LOCATION))((a), (b))

Answer 4

OK, my C is rather rusty, but it seems to me that your IAP_EXECUTE_CMD() macro is casting the unsigned long address as a pointer to a function which returns void and accepts zero arguments. Therefore, any arguments passed to the function call would be too many.