Interrupt Handling in a CPU

Interrupts are an essential part of a computer system, allowing the CPU to handle various events and tasks concurrently. When an interrupt occurs, the CPU suspends its current activities and transfers control to a specific routine called the Interrupt Service Routine (ISR) or Interrupt Handler. The CPU decides when to handle interrupts based on certain conditions.

Types of Interrupts

There are several types of interrupts, including hardware interrupts and software interrupts. Hardware interrupts occur when external devices request attention from the CPU, such as keyboard input or disk I/O. On the other hand, software interrupts are triggered by software instructions, such as system calls or exceptions.

Interrupt Handling Process

The interrupt handling process typically involves the following steps:

1. Interrupt Detection: The CPU continuously monitors for interrupt signals from external devices or internal events. When an interrupt signal is detected, the CPU acknowledges it and suspends its current activities.

2. Interrupt Acknowledgement: After detecting an interrupt, the CPU acknowledges it by storing the interrupt identifier in a specific register called the interrupt register. This allows the CPU to identify the type of interrupt and determine the appropriate ISR to execute.

3. Interrupt Service Routine Execution: Once the interrupt is acknowledged, the CPU transfers control to the corresponding ISR. The ISR is a predefined routine that handles the specific interrupt and performs the necessary tasks. It can save the state of the interrupted program, process the interrupt, and restore the state back to resume the suspended program.

4. Interrupt Return: After the ISR completes its execution, it returns control back to the interrupted program. The CPU restores the saved state and continues the program execution from where it was interrupted.

Handling Interrupts in a CPU

The given question states that a CPU generally handles an interrupt by executing the interrupt service routine by checking the interrupt register after finishing the execution of the current instruction. This means that the CPU follows a specific sequence of steps to handle interrupts:

1. The CPU completes the execution of the current instruction it is processing.

2. At the end of the current instruction, the CPU checks the interrupt register to determine if any interrupt signals have been received.

3. If an interrupt signal is present in the interrupt register, the CPU acknowledges the interrupt and transfers control to the corresponding ISR.

4. The ISR executes to handle the interrupt and perform the necessary actions.

5. Once the ISR completes, the CPU returns control back to the interrupted program and resumes execution.

By checking the interrupt register after finishing the execution of the current instruction, the CPU ensures that it does not interrupt the processing of an instruction in the middle. This approach allows for proper synchronization and prevents any potential issues that may arise from interrupting the execution flow abruptly.