Another factor of concern for realtime systems is the amount
of time taken between the generation of the hardware
interrupt and the first line of code executed by the ISR.
There are two factors to consider here:
- If any thread in the system calls InterruptDisable()
or InterruptLock(), then no interrupts are processed until the
InterruptEnable() or InterruptUnlock()
function call is issued.
- In any event, if interrupts are enabled, the kernel
begins executing the first line of the first ISR (in
case multiple ISRs are associated with an interrupt) in
short order (e.g., under 21 CPU instructions on an x86).