General MCU Query - about Memory

Aamir Ali said:

how allocation is done in memory

It is done by the Linker - so see your Linker manual for details.

Aamir Ali said:

What exactly ram have- initial variables, what else

If you are programming in 'C', the Compiler inserts code to do initialisation - see your Compiler manual for details

Aamir Ali said:

Stack is executed during run time. Only its starting address is defined in MCU

Not sure what you mean by that?

Different tools have different ways to allocate the stack - see your particular tool manuals for details.

Aamir Ali said:

Stack is executed during run time. Only its starting address is defined in MCU

The stack pointer, which is pointing at the 'current top of stack' is initialized by the C startup code (usually to the address right after end of memory, so the first element written to stack appears at top of memory). ifyou program in assembly language, you're responsible for setting the stack pointer to a suitable start address.

However, except for very weird code, stack is never executed. Whenever something is pushed on the stack, the CPU executes something like
memory[--stackpointer]=value;
And when it is fetched back, something like
value = memory[stackpointer++] is done.
where 'memory' points to 0x0000, the start of the addressing range, and 'stackpointer' is the SP register of the CPU. And hopefully, memory[stackpointer] addresses something that is in the memory range occupied by ram - and not used for variables already (stack overflow).

About how the memory is allocated, well, usually, variables are allocated on ram area from bottom up, while the stack is initialized to top of ram and grows down. Until the two meet (which never should happen).

IF you have pre-initialized global variables in your C code, the init values are allocated in flash memory and copied to the proper locations in ram by the C startup code.
initialized local variables are initialized programmatically (the function code itself sets them at start of the function)