What is the role of stack in a microprocessor?

Question

What is the role of stack in a microprocessor?

Answer 1

At the lowest level the stack is the place where certain instructions store or retrieve data and where data is stored when an interrupt occurs. Microprocesors vary, but there are 5 general types of stack-specific instructions:

1. PUSH - put data onto the stack
2. POP (or PULL) - "remove" data from the stack
3. CALL - jump to a subroutine and put the return address on the stack
4. RETURN - return from a subroutine by loading the program counter with the stack top
5. INT (or SWI) - software interrupt; a specialized CALL

When a processor interrupt occurs (due to an external device), the CPU will save the current program counter and (usually) the flags register on the stack and jump to the handling subroutine. This allows the handling subroutine to process the interrupt and return to whatever the CPU was doing with its current state preserved.

While a microprocessor has only one stack active at a time, the operating system can make it appear as if there are multiple stacks. At least one for the OS, one for each process and one for each thread. In fact, the threads themselves may implement multiple stacks.

At a higher level, whatever language is used to implement a thread will often use the stack for its own purposes to store functional call parameters, local variables and function call return values (speaking in broad strokes here -- consult your languages' low-level documentation for specific detail).

Thus concludes my bottom-up explanation of the stack.