22.6.3. Control Operations

In a nutshell basically we store fetch the instruction, decode the instruction and then find out whether some operands has to be fetched from the memory and then fetch the operands do the operation and store it in a memory location.

Instruction execution follows a series of steps. First, the CPU fetches the instruction from memory. This means reading the instruction that the CPU needs to execute next. After fetching, the instruction is decoded to determine what operation needs to be performed. Next, the CPU checks if there are any operands (data needed for the operation) that need to be fetched from the memory. If so, these operands are retrieved. Finally, once the instruction is understood, and all necessary data is available, the CPU executes the instruction and stores any results back in memory, if required.

You can think of this process like following a recipe. First, you read the recipe (fetching the instruction), then you figure out what needs to be done (decoding the instruction), check if you have all the ingredients (fetching operands), and then you cook (execute the instruction) and serve the food (store the results).

So generally from the users perspective we see that instruction 1, then instruction 2, then instruction 3 it will keep on going if there is a jump instruction you will jump to the position again come back and so forth.

The fetch-decode-execute cycle is fundamental to how a CPU processes instructions. Each instruction is handled in a loop — the CPU continuously retrieves the next instruction from memory, decodes what the instruction is supposed to do, and then executes it. If there is a jump instruction, the CPU will modify the flow of execution by jumping to a different part of the program temporarily. This cycle continues until the program has completed all its instructions.

Imagine watching a movie where each scene is an instruction. You watch one scene, then the next, and so on in order. However, if a character decides to flashback to a previous event (just like a jump instruction), you pause the current timeline to explore that scene before returning to where you left off.

So, therefore, interrupt means not only servicing interrupt you have to store back everything.

Interrupts allow the CPU to pause its current task to address important events, like input from a mouse or keyboard. When an interrupt signal is received, the CPU saves its current state (like a bookmark) so it can return once the interrupt is handled. After processing the interrupt, the CPU retrieves the saved state and continues executing the original instruction.

Think of it like a person working on an important project who suddenly receives a phone call. They pause their work (the interrupt), jot down important details about the call (handling the interrupt), and afterward return to their project, picking up right where they left off.

So, you will be also able to express indirect mode of instruction execution, direct mode means some operands will be the values of the operands will be either in the instruction or you can directly find the value of the instruction operands in the memory.

In computer architecture, addressing modes determine how the operand of an instruction is accessed. Direct addressing mode means the operand's actual value is provided in the instruction itself. In contrast, indirect addressing mode means the instruction provides a memory address that points to where the operand's value is stored. This allows for fetching larger or more complex datasets efficiently.

You can think of direct addressing like having the exact recipe in your hand with all the quantities listed (direct). Indirect addressing is more like a treasure map where you have clues (addresses) that lead you to the actual recipe hidden elsewhere.

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