How does this vector table initialization code works?

[Dennis Dewey]

The code snippet below is initializing a vector interrupt table a location 0x00000000, and I quite don't understand the syntax. I understand that g_pfnVectors is an array of constant pointers to void. I don't understand the (void) just before the equal sign? The other statement that I don't understand it the casting of __STACK_TOP. It looks like it's casting it to an unsigned long void pointer to void, but what I don't get is the '&' in front of __STACK_TOP?

#pragma DATA_SECTION(g_pfnVectors, ".intvecs")
void (* const g_pfnVectors[])(void) =
{
(void (*)(void))((unsigned long)&__STACK_TOP),

ResetISR,
NmiSR,
FaultISR,
IntDefaultHandler,
IntDefaultHandler,
IntDefaultHandler,
0,
0,
0,
0,
IntDefaultHandler,
IntDefaultHandler,
0,

};

[Banfa]

I understand that g_pfnVectors is an array of constant pointers to void

In that case what you understand is wrong.

It is an array of pointers to functions that take no parameters and return nothing, i.e. the prototype is void fn(void);. That is why there are brackets round the g_pfnVectors bit of the declaration and the void in brackets afterwards is declaring the parameter list.

It is not unknown for the first entry in the interrupt table of a microprocessor to point to the program, so in this case I guess that __STACK_TOP equates to the start of the program. This sort of variable is often highly platform dependent, the & gets the address of __STACK_TOP which is presumably the start of the program.

What platform does this run on?

[Dennis Dewey]

Banfa, Thank-you for your reply. Your explanation clear it up perfectly. The code snippet is from Stellaris ARM Cortex-M3 LM3S811 processor startup code. The memory model layout has the stack location at address zero followed by exception function handlers.