Interrupt Handling

Interrupt handling is a critical mechanism in embedded systems, allowing them to react to external and internal events efficiently and in real-time. It enables a system to temporarily halt its current execution flow to address a more urgent task, known as an interrupt. When an event triggers an interrupt, the system’s processor suspends its current activities, saves its state, and transfers control to a designated interrupt service routine (ISR). This routine processes the event and restores the system to its prior state. This capability is essential for embedded systems, which often operate under real-time constraints, requiring immediate and predictable responses to external stimuli. Interrupt handling is implemented at both hardware and software levels, with hardware providing the necessary mechanisms to detect interrupt signals, and software managing the prioritization and execution of ISRs.

Common Applications

Real-Time Systems

In real-time systems, such as automotive control units and industrial automation, interrupt handling is vital for meeting precise timing requirements. It ensures that critical tasks are executed within a specified deadline.

Communication Protocols

Interrupts are used in communication protocols to manage data transmission and reception. They can signal when data is available to be read or when a buffer is ready to accept new data, facilitating efficient data handling.

User Interface Devices

Devices like keyboards and mice rely on interrupt handling to detect and respond to user inputs promptly. Each keypress or mouse movement generates an interrupt, allowing the system to process the input immediately.

Safety Considerations

Priority and Masking

Proper prioritization and masking of interrupts are crucial to ensure that critical interrupts are handled before less critical ones. Failure to prioritize can lead to missed deadlines and system instability.

Interrupt Latency

Minimizing interrupt latency, the time between an interrupt request and the start of its handling, is essential for maintaining system responsiveness. Excessive latency can result in delayed responses and potential safety hazards.

Reentrancy and Concurrency

ISRs must be designed to be reentrant and handle concurrency issues, as they can be interrupted by other higher-priority ISRs. Failure to do so can lead to data corruption and unpredictable behavior.

Related Terms or Concepts

Interrupt Service Routine (ISR)

An ISR is a specific function or routine that executes in response to an interrupt. It contains the code required to handle the specific event that triggered the interrupt.

Interrupt Vector

The interrupt vector is a data structure used to hold the addresses of ISRs. It enables the processor to locate and execute the appropriate ISR in response to an interrupt.

Polling

Polling is an alternative to interrupt handling, where the system continuously checks the status of an input to detect events. While simpler, polling can be less efficient as it consumes more CPU resources and may increase response time.

Context Switching

Context switching involves saving the state of the current execution and loading the state of another task or interrupt. Efficient context switching is crucial for effective interrupt handling to ensure minimal system disruption.