Instruction Cycle - Interrupt

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In a instruction cycle, the interrupt is the last part.

Interrupts occur at random times during the execution of a program, in response to signals from hardware.

Type Mean of Communication between
Interrupts the CPU and the OS kernel
Signals the OS kernel and OS processes

An interrupt is an indication to a thread that it should stop what it is doing and do something else. It's up to the programmer to decide exactly how a thread responds to an interrupt, but it is very common for the thread to terminate.

Interrupts may be initiated by;

  • the CPU (exceptions - e.g.: divide by zero, page fault),
  • devices (hardware interrupts - e.g: input available),
  • or by a CPU instruction (traps - e.g: syscalls, breakpoints).

They are eventually managed by the CPU, which “interrupts” the current task, and invokes an OS-kernel provided ISR/interrupt handler.

Instruction Cycle


Interrupt process from Keyboard to Process

After USB host (computer’s USB “port”) receives the data from keyboard, it generates a hardware interrupt so that software driver in operating system can read the received data via host controller interface (usually over PCI or PCIe). After that, the data is processed by Human Interface Device (HID) subsystem in the OS which eventually results in placing a “key pressed” event (like WM_KEYDOWN) in operating system’s message queue. Then the event is dispatched by event loop to active application window.



When a call is made to an interrupt, the processor automatically saves the state of the EFLAGS register on the procedure stack.

Documentation / Reference

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