System Interrupts

• What are interrupts? 

  • An interrupt is a signal to the processor that stops its current task and performs a different task temporarily 
  • Interrupts can be hardware events or time-sensitive tasks 
  • When an interrupt occurs, the processor suspends the current program execution and transfers control to an interrupt service routine 
• Purpose and Role of Interrupts 

  • Real-time Event Handling: hardware errors and signals from input devices e.g. hard disk failure 
  • Device Communication: alerts from external devices e.g. printer jams and network errors 
  • Multitasking: suspending processing in one application so that the user can switch to another
• Interrupts types Image

  
• The Interrupt Process #1

  1. Interrupt Request (IRQ) 

  • An external device or software generates an interrupt, signalling the processor to stop its current task 
  • The interrupt controller passes this to the interrupt handler for assessment 

  2. Interrupt Acknowledge

  • The interrupt handler decides if the interrupt needs to be dealt with now or later 
  • If yes, the current contents of the processor registers are saved in memory 
• The Interrupt process #2

  
  

  3. Interrupt Service Routine (ISR) Lookup 

  • The processor fetches the corresponding Interrupt Service Routine (ISR) associated with the interrupt type 

  4. ISR Execution 

  • The processor transfers control to the ISR and executes the routine to handle the specific interrupt 

  5. Interrupt Exit

  • After the ISR completes, the processor restores the content of the registers from step 2 
  • The fetch-decode-execute cycle is resumed
• Interrupt process Image

  
• What is an ISR? 

  • An ISR is a special function that handles a particular interrupt type 
  • Each type of interrupt has a corresponding routine, e.g. printer jam, hard disk failure, file download error, network connection error all have routines to be followed when they happen 
  • ISRs should be concise, efficient, and carefully designed to minimise the time taken to execute, as they often need to handle time-sensitive events 
• Interrupt priority and nesting 

  • Interrupt prioritisation means the processor can acknowledge and switch to resolving a higher-priority interrupt 
  • Prioritising interrupts is vital because many things can go wrong at the same time 
  • Lower-priority ISRs may be temporarily suspended until the higher-priority ISR completes the execution 
  • Nesting of interrupts refers to the ability of the processor to handle interrupts within interrupts 
  • Proper management of nested interrupts avoids potential conflicts and ensures system stability 
• Interrupt priority handling Image