Question

I have microcontroler that I am working with. When debugging it is necessary to call a function from that is hard coded in ROM. Technical Reference shows how to do this:

# define Device_cal (void(*)(void))0x3D7C80

and calling procedure looks like this:

(*Device_cal)()

I can’t understand what actually happens here, so my question is:
How does it work?

Answer 1

The #define causes (*Device_cal)() to be expanded into this immediately before compiling:

(*(void(*)(void))0x3D7C80)()

The void(*)(void) is a declaration for a function pointer that takes void and returns void types. The (*()) represents a cast for the next token in the expression (0x3D7C80). Thus this asks to treat the data at location 0x3D7C80 as a function. The final () calls the function with no arguments.