InterruptServiceRoutinen

An Interrupt Service Routine (ISR) is a small software function that runs in response to an interrupt, a signal from hardware or software requiring immediate attention. The term InterruptServiceRoutinen can appear in non-English documentation as the plural form of the routine. An ISR typically executes at high priority and in an interrupt context, meaning normal program flow is temporarily suspended while the routine runs.

Responsibilities include quickly acknowledging the interrupt, reading or writing hardware registers, clearing interrupt flags, and performing a minimal amount of work to restore normal operation. ISRs should execute quickly and avoid blocking calls, long loops, or operations that may sleep. If more processing is needed, the ISR should schedule work to be done later by another thread or a deferred mechanism (for example, a task queue or a bottom-half handler), and then return control to the main program.

Design considerations cover timing, reentrancy, and data integrity. ISRs must preserve processor state and avoid assumptions about the environment inside the interrupt. Access to shared data should be synchronized, typically with atomic operations or memory barriers, and any used resources should be carefully managed to avoid deadlock or priority inversion. Depending on the platform, interrupts may be nested or masked during an ISR, and the vector or IRQ mechanism often defines how interrupts are dispatched.

On microcontrollers, ISRs are typically registered in a vector table, providing deterministic latency and simple hardware interaction. In modern operating systems, ISRs may be paired with threaded or deferred handlers to smooth latency budgets and to enable blocking operations in a controlled context.