Interrupts

Definition

Interrupts are signals sent to the processor that temporarily halt its current activities to allow it to respond to a more urgent task. This feature is essential for managing interactions with hardware devices like LEDs, switches, and keypads, enabling the system to react promptly to external events without constantly polling devices for status updates.

5 Must Know Facts For Your Next Test

1. Interrupts allow embedded systems to efficiently manage multiple tasks by prioritizing urgent events over regular processing.
2. When an interrupt occurs, the current state of the processor is saved so that it can resume work after handling the interrupt.
3. Hardware interrupts are generated by external devices (like switches) while software interrupts are triggered by programs when they need immediate attention from the CPU.
4. Using interrupts can significantly improve system responsiveness compared to polling, as the CPU can perform other tasks until an interrupt is received.
5. Different types of interrupts include maskable interrupts, which can be ignored by the processor, and non-maskable interrupts, which cannot be ignored and must be addressed immediately.

Review Questions

• How do interrupts improve the efficiency of embedded systems when interfacing with devices like switches and keypads?
  • Interrupts enhance efficiency by allowing the processor to focus on other tasks while waiting for an external event, like a switch press. Instead of constantly polling the switch for changes, which wastes CPU cycles, the system can remain idle until an interrupt signals that a switch state has changed. This leads to better resource management and a more responsive system overall.
• Discuss the role of Interrupt Service Routines (ISRs) in handling interrupts generated by hardware devices. What are some considerations when designing ISRs?
  • ISRs are critical for responding to hardware-generated interrupts. They execute specific tasks related to the interrupting device, such as reading a key press from a keypad or updating an LED state. When designing ISRs, it's important to keep them short and efficient to minimize delay in returning control to the main program. Additionally, care must be taken regarding shared resources and potential race conditions since ISRs can interrupt normal processing.
• Evaluate how the use of interrupts vs. polling affects overall system performance in embedded applications that require user interaction through switches and keypads.
  • Using interrupts typically leads to better performance compared to polling, particularly in applications requiring quick user interaction. Interrupts allow the system to respond immediately when a user interacts with a switch or keypad, while polling can introduce latency as the CPU may not check device status frequently enough. This responsiveness is crucial in real-time applications where timely feedback is necessary for user satisfaction. Moreover, using interrupts frees up CPU time for other tasks, enhancing overall system efficiency.

Related terms

Polling: A method where the CPU repeatedly checks the status of a device to determine if it needs attention, which can be less efficient than using interrupts.

Interrupt Service Routine (ISR): A special function that is executed in response to an interrupt, allowing the processor to handle the event and return to its previous task after the ISR completes.

Context Switching: The process of saving the state of a currently running task so that it can be resumed later, which is necessary when an interrupt occurs and the processor switches tasks.