7.1 Interrupt concepts and types
2 min read•august 7, 2024
Interrupts are crucial in embedded systems, allowing processors to respond to external events and exceptional conditions. They come in various types, including hardware and software interrupts, maskable and non-maskable interrupts, and edge-triggered and level-triggered interrupts.
Efficient interrupt handling is key to system responsiveness. This involves using interrupt vectors, minimizing latency, and employing interrupt controllers to manage multiple interrupt sources. Understanding these concepts is essential for designing robust embedded systems.
Interrupt Types
Hardware and Software Interrupts
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- Hardware interrupts are generated by external hardware devices (timers, keyboards, sensors) to request service from the processor
- Occur asynchronously and are not related to the currently executing instruction
- Software interrupts, also known as exceptions, are generated by software instructions or exceptional conditions (division by zero, invalid memory access, system calls)
- Triggered synchronously by the currently executing instruction
Maskable and Non-Maskable Interrupts
- Maskable interrupts can be temporarily disabled or ignored by the processor using the interrupt mask register
- Allows the processor to complete critical tasks without interruption
- Non-maskable interrupts (NMIs) cannot be disabled and must be serviced immediately
- Reserved for critical events (power failure, hardware errors) that require immediate attention
Edge-Triggered and Level-Triggered Interrupts
- Edge-triggered interrupts are detected by the processor on the rising or falling edge of the interrupt signal
- Require the interrupt signal to transition from one state to another (low to high or high to low)
- Level-triggered interrupts are detected by the processor based on the level (high or low) of the interrupt signal
- Remain active as long as the interrupt signal maintains the specified level
- Edge-triggered interrupts are less susceptible to spurious interrupts caused by noise or glitches compared to level-triggered interrupts
Interrupt Handling
Interrupt Vector and Latency
- An is a table stored in memory that contains the addresses of interrupt service routines (ISRs) for each interrupt
- When an interrupt occurs, the processor uses the interrupt vector to determine the address of the corresponding ISR
- is the time delay between the occurrence of an interrupt and the start of the ISR execution
- Latency is affected by factors (current processor state, interrupt priority, hardware )
- Minimizing interrupt latency is crucial for real-time systems that require prompt responses to events
Interrupt Controller
- An interrupt controller is a hardware component that manages and prioritizes multiple interrupt sources
- Receives interrupt requests from various devices and notifies the processor based on predefined priorities
- Allows the processor to handle interrupts efficiently by providing features (interrupt masking, priority levels, vectored interrupts)
- Examples of interrupt controllers include the Programmable Interrupt Controller (PIC) in x86 architectures and the Nested Vectored Interrupt Controller (NVIC) in ARM Cortex-M processors
Key Terms to Review (18)
Context Switching: Context switching is the process of storing the state of a currently running task or process so that it can be resumed later, allowing multiple tasks to share a single CPU. This mechanism is crucial for multitasking operating systems and plays a significant role in managing interrupts, exceptions, and task scheduling.
Edge-triggered interrupt: An edge-triggered interrupt is a type of interrupt that is triggered by a change in the signal level, such as a transition from low to high or high to low. This mechanism allows a system to respond quickly to specific events without the need for constant polling, making it efficient for managing resources and processing tasks in real-time applications.
Hardware interrupt: A hardware interrupt is a signal sent to the processor by hardware devices, indicating that an event needs immediate attention. This mechanism allows the CPU to respond promptly to important events, such as input from a keyboard or mouse, thereby improving the overall efficiency and responsiveness of a system. Hardware interrupts are essential for managing multiple tasks and ensuring that time-sensitive processes are prioritized effectively.
Interrupt latency: Interrupt latency refers to the time delay between the occurrence of an interrupt and the start of the corresponding interrupt service routine (ISR). This delay is critical in real-time systems, where timely response to events is essential, and it can be influenced by factors like interrupt priority, system load, and the handling of other interrupts.
Interrupt overhead: Interrupt overhead refers to the additional processing time and resources consumed by a system when an interrupt is triggered, leading to context switching and execution of an interrupt service routine. This overhead can impact overall system performance and responsiveness, especially in embedded systems where timing and efficiency are critical. Understanding interrupt overhead is essential for optimizing system design and ensuring that high-priority tasks are not delayed by excessive interrupt handling.
Interrupt prioritization: Interrupt prioritization is the method by which a microcontroller or processor determines the order in which multiple interrupts are handled based on their urgency or importance. This system ensures that higher priority interrupts can interrupt lower priority ones, allowing time-sensitive tasks to be addressed promptly while preventing less critical processes from delaying important operations.
Interrupt Service Routine (ISR): An Interrupt Service Routine (ISR) is a special block of code that gets executed in response to an interrupt signal, allowing the system to respond to external events quickly. ISRs are crucial for managing time-sensitive tasks without disrupting the main program flow, ensuring efficient use of processing resources in applications that require immediate attention, like handling timers or responding to hardware signals.
Interrupt Vector: An interrupt vector is a specific memory address used by the processor to identify the location of an interrupt service routine (ISR) for handling various types of interrupts. This allows the processor to quickly locate and execute the appropriate code when an interrupt occurs, ensuring efficient response to events like hardware signals or software exceptions. The use of interrupt vectors is crucial for managing multiple interrupts effectively, allowing different ISRs to be executed based on the type of interrupt received.
Interrupt-driven programming: Interrupt-driven programming is a method where a system's CPU responds to external or internal events by temporarily halting its current execution flow, allowing it to execute a special routine called an interrupt handler. This approach enables embedded systems to react promptly to real-time events while optimizing CPU usage by only processing tasks when necessary. It supports the design of responsive systems that can handle multiple tasks efficiently, ensuring that critical functions receive immediate attention.
Level-triggered interrupt: A level-triggered interrupt is a type of interrupt that is activated when a signal remains at a particular voltage level, indicating the occurrence of an event that requires processing. This means that as long as the signal stays at the active level, the interrupt will continue to be asserted, which can be useful for certain types of hardware interactions. Unlike edge-triggered interrupts, which respond to changes in signal state, level-triggered interrupts are persistent until cleared, making them reliable for handling ongoing conditions.
Maskable interrupt: A maskable interrupt is a type of interrupt in computer systems that can be enabled or disabled by the processor using a control mechanism, allowing for selective response to events. This feature allows the system to prioritize certain tasks and manage critical operations without being interrupted by less important signals. Maskable interrupts are essential for efficient system performance, as they enable the processor to handle time-sensitive operations while ignoring irrelevant ones.
Microcontroller architecture: Microcontroller architecture refers to the design and organization of a microcontroller, which integrates a processor core, memory, and input/output peripherals on a single chip. This architecture is crucial as it determines how the microcontroller processes information, communicates with other components, and manages tasks like interrupts, which are essential for responsive and efficient operations in embedded systems.
Nested interrupts: Nested interrupts refer to the ability of a microcontroller or processor to allow higher-priority interrupts to be serviced while a lower-priority interrupt is being handled. This capability enhances responsiveness and efficiency in embedded systems by enabling critical tasks to preempt ongoing lower-priority tasks, ensuring timely processing of events. Understanding how nested interrupts work is vital for managing interrupt priority levels, effectively implementing ISRs, and utilizing timer interrupts and callbacks efficiently.
Non-maskable interrupt: A non-maskable interrupt (NMI) is a high-priority interrupt that cannot be ignored or disabled by standard interrupt masking techniques. NMIs are crucial for handling critical events, such as hardware failures or emergency conditions, ensuring that the system responds immediately. This feature allows embedded systems to maintain reliability and stability in the face of unexpected issues.
Polling: Polling is a method used in embedded systems to repeatedly check the status of a device or input, such as switches or sensors, at regular intervals. This technique allows a microcontroller to determine whether an event has occurred, but it can be resource-intensive since it occupies the CPU with continuous checks instead of allowing it to perform other tasks. Polling connects directly to controlling and interfacing with hardware components, timing operations, managing GPIO states, and differentiating from interrupt-driven designs.
Real-Time Operating Systems: Real-time operating systems (RTOS) are specialized operating systems designed to manage hardware resources and execute tasks with strict timing constraints. They ensure that critical tasks are completed within a defined time frame, which is essential for applications requiring immediate processing, such as embedded systems in automotive, medical devices, and industrial control. An RTOS can handle multiple tasks concurrently while prioritizing them based on their urgency, thus playing a vital role in embedded systems that rely on predictable behavior and responsiveness.
Response Time: Response time is the duration it takes for a system to react to an input or stimulus, often measured from the moment an event occurs until the system produces an output. This measure is critical for ensuring that systems behave predictably and meet operational requirements, especially under constraints where timely responses are essential for functionality.
Software interrupt: A software interrupt is a mechanism that allows a program to signal the processor to stop executing its current tasks and execute a specific routine instead, often referred to as an interrupt service routine (ISR). This mechanism is useful for handling events such as input/output operations or errors, and it enables the system to respond quickly to critical conditions without polling. Software interrupts are an essential part of the interrupt-driven programming model, allowing seamless communication between software processes and the hardware.