11. interrupts_and_stacks_flashcards
What is a system interrupt?
A signal sent to the CPU to temporarily halt current execution and handle important tasks.
Why are system interrupts needed?
They allow the CPU to manage multiple tasks efficiently by switching between them.
What are the two ways a computer can manage multiple tasks?
- Multiple processors (expensive and power-hungry). 2. Single processor with interrupts (uses context switching).
What is context switching?
The process where the CPU saves the state of a process before switching to another task.
What is the purpose of the Program Control Block (PCB)?
It keeps track of a process’s state, allowing seamless execution after context switching.
What information is saved during context switching?
Program Counter (PC), registers, and Stack Pointer (SP).
Why must the CPU save information during context switching?
To restore execution later without losing progress.
What are the sources of interrupts?
Timers, input/output interfaces, user programs, and hardware failures.
What is the Interrupt Vector Table?
A table that helps the CPU locate the correct Interrupt Service Routine (ISR).
What are the basic steps in handling an interrupt?
- Save context, 2. Identify ISR, 3. Execute ISR, 4. Restore context, 5. Resume execution.
What is an Interrupt Mask?
A register that enables or disables interrupts to prioritize or block lower-level IRQs.
Why use an Interrupt Mask?
To prevent lower-priority interrupts from disrupting critical operations.
Give an example of a task that should not be interrupted.
Boot code execution, ISR execution, and high-priority time-critical tasks.
What is the revised Fetch-Decode-Execute (FDE) cycle?
A modified cycle that includes checking and handling interrupts.
Where is the processor context stored during an interrupt?
In the PCB, which is implemented as a stack.
What is the role of the system stack?
To store return addresses, processor context, and temporary variables.
How does the stack grow and shrink?
It grows downward as values are pushed and shrinks upward when values are popped.
What does the Stack Pointer (SP) do?
Tracks the top of the stack and updates when data is pushed or popped.
How is data pushed onto the stack?
Decrement SP and store data at the new address.
How is data popped from the stack?
Retrieve data from SP and increment SP.
Why is saving the return address important?
It allows the CPU to resume execution of the original task after handling the interrupt.
What are the two main tasks of an Interrupt Service Routine (ISR)?
Handling the interrupt source and returning to the interrupted task.
What instruction is used to return from an interrupt?
RETURN instruction, which restores the saved context from the stack.
What happens when the CPU detects an interrupt?
It completes the current instruction, saves context, executes ISR, restores context, and resumes execution.
