I have a question like that:
When does the CPU execute an interrupt service routine?
a) After the instruction decoding phase, before the instruction execution phase
b) After completion of the last phase of order execution
c) After the fetching phase, before the decoding phase of the currently processed instruction
d) After completion of the order execution phase, before the next order download phase
I think the right answer is c) but I cannot find any confirmation
>Solution :
The CPU executes an interrupt service routine (ISR) in response to an interrupt signal. Interrupts are signals that are generated by various sources, such as hardware devices or software events, to gain the attention of the CPU and request immediate processing.
There are several types of interrupts, including hardware interrupts, software interrupts, and exceptions. Here are some common scenarios when the CPU executes an ISR:
1. Hardware Interrupts: These interrupts occur when an external hardware device, such as a keyboard, mouse, or network card, sends a signal to the CPU. Examples of hardware interrupts include keyboard input, timer expiration, disk I/O completion, or network data arrival.
2. Software Interrupts: Also known as software-generated interrupts or traps, these interrupts are initiated by software instructions or system calls. For example, when a program needs to perform a privileged operation, it triggers a software interrupt to transition into the kernel mode and execute the corresponding ISR.
3.Exceptions: Exceptions are interrupt-like events that occur in response to specific conditions or exceptional situations during program execution. Examples include divide-by-zero errors, page faults (when accessing virtual memory), or illegal instruction execution.
When an interrupt occurs, the CPU suspends its current task, saves the necessary context (registers, program counter, etc.), and transfers control to the corresponding ISR. The ISR executes the necessary actions to handle the interrupt, which may involve servicing the hardware request, processing the software event, or handling the exceptional condition. Once the ISR completes, the CPU restores the saved context and resumes the interrupted task.
Interrupt handling allows the CPU to handle multiple concurrent tasks efficiently and respond promptly to external events and requests.
Yes, Right answer is c) After the fetching phase, before the decoding phase of the currently processed instruction.
The CPU executes an interrupt service routine (ISR) during the interrupt processing mechanism. When an interrupt signal occurs, the CPU suspends its current execution and saves the necessary context. This happens after the fetching phase (where the next instruction is fetched from memory) and before the decoding phase (where the fetched instruction is decoded). The ISR is executed to handle the interrupt, and once it completes, the CPU resumes the interrupted execution by continuing with the decoding phase of the original instruction.