Interrupt handler
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An Interrupt Handler is the modern progression of an interrupt service routine, a routine whose execution is triggered by an interrupt.
In modern systems Interrupt Handlers are split into two parts: the First-Level Interrupt Handler (FLIH) and the Second-Level Interrupt Handlers (SLIH).
The FLIH operates in the same way as the old interrupt routines did. In response to an interrupt there is a context switch and the code for the interrupt is loaded and executed. The job of the FLIH, however, is not to process the interrupt, but to schedule the execution of the SLIH, while recording any critical information which is only available at the time of the interrupt.
The SLIH sits on the run queue of the operating system until it can be executed to perform the processing for the interrupt when processor time is available.
It is worth noting that in many systems the FLIH and SLIH are referred to as upper halves and lower halves, or a derivation of those names.de:Unterbrechungsroutine