Sequence of events when an interrupt hits?

• Foreground code is running, interrupts are enabled
• Interrupt event sends an interrupt request to the CPU
• After completing the current instruction(s), the CPU begins the interrupt response
  • automatically saves current program counter
  • automatically saves some status (depending on CPU)
  • jump to correct interrupt service routine for this request
  • ISR code saves any registers and flags it will modify
  • ISR services the interrupt and re-arms it if necessary
  • ISR code restores any saved registers and flags
  • ISR executes a return-from-interrupt instruction or sequence
  • return-from-interrupt instruction restores automatically-saved status
  • return-from-interrupt instruction recovers saved program counter
• Foreground code continues to run from the point it responded to the interrupt

Courtesy: http://www.scriptoriumdesigns.com/embedded/interrupts.php

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