Why does the location of the handler within the source file, matter?

Consider:



When the two function prototypes (set and Reset) are repositioned to appear before the handler, I get issues, exceptions etc, why?

 

I don't quite understand the problem.

Normally, function prototypes are placed at the start of the source file or in a header file. They must be declared before the function is called.

Can you state which function call is giving you problems?
Set( ) and Reset( ) are not library functions. Where are they implemented?

What IDE platform are you using?

 

I don't quite understand the problem.

Normally, function prototypes are placed at the start of the source file or in a header file. They must be declared before the function is called.

Can you state which function call is giving you problems?
Set( ) and Reset( ) are not library functions. Where are they implemented?

What IDE platform are you using?

I've just discovered this is an odd side effect of how the src is compiled. When the project is created the files are by default "compiled as C++" even though the code is pure C. Changing that build to "compile as C" resolves the problem.

The problem was (before I tweaked the "Build as" setting) that positioning those two prototypes before the handler, causes a runtime exception, like it doesn't "see" the handler, but moving them to after the handler, it runs fine.

I use Visual Studio with VisualGDB.

 

Here's the crash when debugging:



Simply making that handler the very first function (even before any prototypes) it all runs fine.

 

Seems this is the explanation:

https://electronics.stackexchange.com/a/7695

 

Ahh, its making a bit more sense. I've pretty much never used C++, so didn't grasp the semantics of this:



It wasn't clear to me that that ifdef applies the extern "C" to the very next thing in the file, I saw it and interpreted it as some global directive for the whole file, but it isn't. So it was nothing whatsoever to do with it being "first" but with whether the func had that extern "C" prefix.

 

Being a bit OCD about these things, I'd have written this in these samples as:

#ifdef __cplusplus
extern "C" void SysTick_Handler(void)
{
    HAL_IncTick();
    HAL_SYSTICK_IRQHandler();
}
#else
void SysTick_Handler(void)
{
    HAL_IncTick();
    HAL_SYSTICK_IRQHandler();
}
#endif

Perhaps overkill but certainly clearer and better for beginners. Anyway, I did learn something so that's a plus!