Sage-Tips

What causes an interrupt to the CPU?

Interrupts are signals sent to the CPU by external devices, normally I/O devices. They tell the CPU to stop its current activities and execute the appropriate part of the operating system. Software Interupts are generated by programs when they want to request a system call to be performed by the operating system.

What happens when CPU gets interrupt?

When an interrupt occurs, it causes the CPU to stop executing the current program. The control then passes to a special piece of code called an Interrupt Handler or Interrupt Service Routine. The state of the process includes all registers that the process may be using, including the program counter (PC).

How is an interrupt generated?

An interrupt is a signal sent to the processor that interrupts the current process. It may be generated by a hardware device or a software program. A hardware interrupt is often created by an input device such as a mouse or keyboard. An interrupt is sent to the processor as an interrupt request, or IRQ.

What does the CPU do immediately before handling an interrupt?

CPU: The CPU looks up the device handler address in the interrupt vector table using the vector as an index. A subroutine-like mechanism is used to save the current value of the PC and possibly other internal CPU state, such as general-purpose registers.

What happens if an interrupt is activated while the CPU is serving another interrupt?

Because of the automatic decrementing of the stack pointer by each interrupt and subsequent incrementing by the RETURN instruction, the first interrupt service routine is resumed after the second interrupt is completed, and the interrupts are serviced in the proper order.

How many times does a clock interrupt occur in a second?

Many processors have internal logic to generate an interrupt after a certain number of CPU clock cycles have passed. it is common to program such logic to generate a clock interrupt, perhaps 1000 times a second. I suppose this is “outside the CPU” but still inside the processor Many operating systems no longer use periodic clock interrupts at all.

What is a clock interrupt in computer architecture?

A clock interrupt is generally produced by an external component that is programmed to produce a physical signal to the CPU at some desired fixed interval of time (hence the “clock.”)

How does a CPU perform an interrupt?

In simple systems the CPU, as part of its logic, pushes all the registers on the stack including the PC+1, and then “jumps to interrupt” the interrupt routine normally using a vector table. After the interrupt routine runs the “return from interrupt” pulls the registers in reverse order so they are restored.

What happens when the clock interrupt service routine exits?

However, if the OS left suitable instructions, the clock interrupt service routine will save away the state of the user program and load the state of (typically) the OS scheduler. Then, when the clock interrupt exits, the CPU will “resume” running the OS scheduler, which might decide to run a different user process, or whatever.