How Interrupt Works ?

 

In an Embedded System, a Microcontroller or Microprocessor uses the Input/Output pins to interact with the outer world and the other devices. Output pins take the data or information out and input pins to read the data or information. Software on the microprocessor runs at a very high speed than the hardware interactions. A few milliseconds of delay with the hardware could be thousands of instructions for the software. So for optimal hardware and software interaction, there is a mechanism called interrupts.

An interrupt is a signal that temporarily halts the normal execution of a program and directs the MCU to execute a specific piece of code, called an interrupt handler or interrupt service routine (ISR). Interrupts are typically triggered by external events, such as a button press, a sensor reading, or a timer expiration.

Interrupt Sources can be classified into two main categories :

  • Internal interrupt: sources are generated by the MCU itself, such as a timer overflow or a hardware fault.
  • External interrupt: sources are generated by external devices or signals, such as a button press or a sensor reading.
MCUs usually have an interrupt controller that is responsible for managing and prioritizing interrupt requests. When an interrupt occurs, the interrupt controller receives the interrupt request and checks its priority level against the currently executing code. If the interrupt has a higher priority than the current code, the MCU suspends the current execution and jumps to the ISR associated with the interrupt.

Interrupt latency is the time it takes for the MCU to respond to an interrupt request. It is important to keep interrupt latency as short as possible to ensure real-time responsiveness. Interrupt latency can be affected by several factors, such as the interrupt controller’s performance, the interrupt priority scheme, and the amount of time required to save and restore the CPU state.

Interrupt priority determines which interrupt request is serviced first when multiple interrupt requests occur simultaneously. Priority levels are assigned to each interrupt source, and the interrupt controller uses these priority levels to determine which interrupt request to service first. Interrupt priority can be fixed or programmable, depending on the MCU architecture.

Interrupt Vector Table is a table that contains the addresses of the ISRs associated with each interrupt source. When an interrupt occurs, the MCU uses the interrupt number to index into the interrupt vector table to find the address of the ISR associated with the interrupt. The MCU then jumps to the ISR to handle the interrupt.

For more details, refer the link shared below:

https://embeddedwala.com/Blogs/embeddedsystem/how-interrupt-works

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