Interrupt service routine (ISR)

Updated: October 26, 2022

The ISR is a piece of code that's responsible for clearing the source of the interrupt.

This is a key point, especially in conjunction with this fact: the interrupt runs at a priority higher than any software priority. This means that the amount of time spent in the ISR can have a serious impact on thread scheduling. You should spend as little time as possible in the ISR. Let's examine this in a little more depth.

Note: (QNX Neutrino 7.1 or later) The kernel saves and restores the FPU context on entering and leaving ISRs, so it's safe to use floating-point operations in them.