What is the concept of deterministic interrupt latency and how is it minimized in a mission computer?

What is the concept of deterministic interrupt latency and how is it minimized in a mission computer?

• A. Fixed maximum latency does not apply to interrupts.
• B. Interrupt latency should vary with system load.
• C. Deterministic interrupts require long critical sections.
• D. Fixed maximum latency for interrupts; minimize with high-priority interrupts, minimal nesting, deterministic ISR, and avoidance of long critical sections.

Answer: (D)

Deterministic interrupt latency is about guaranteeing a fixed upper bound on the time from when an interrupt occurs to when the system starts handling it, regardless of what else the system is doing. In a mission computer, this predictability is crucial so that critical events are acknowledged within a known time window. To minimize this latency, design and implement the interrupt system to keep that worst-case bound as small as possible. Give the most important interrupts the highest priority so they can preempt less important work and start handling quickly. Avoid deep or frequent nesting of interrupts, because each nested interrupt adds to the total time before the original interrupt can be serviced. Make the interrupt service routine itself deterministic: it should be short, fast, non-blocking, and free of operations that could pause or delay completion. If more processing is needed, defer it to lower-priority tasks or to a later, scheduled step rather than doing it inside the ISR. Keep critical sections (periods where interrupts are disabled) as short as possible to prevent delaying other interrupts. By combining fixed upper-bound timing, high-priority handling, minimal nesting, a concise ISR, and avoiding long critical sections, you achieve true deterministic interrupt latency.

Deterministic interrupt latency is about guaranteeing a fixed upper bound on the time from when an interrupt occurs to when the system starts handling it, regardless of what else the system is doing. In a mission computer, this predictability is crucial so that critical events are acknowledged within a known time window.

To minimize this latency, design and implement the interrupt system to keep that worst-case bound as small as possible. Give the most important interrupts the highest priority so they can preempt less important work and start handling quickly. Avoid deep or frequent nesting of interrupts, because each nested interrupt adds to the total time before the original interrupt can be serviced. Make the interrupt service routine itself deterministic: it should be short, fast, non-blocking, and free of operations that could pause or delay completion. If more processing is needed, defer it to lower-priority tasks or to a later, scheduled step rather than doing it inside the ISR. Keep critical sections (periods where interrupts are disabled) as short as possible to prevent delaying other interrupts. By combining fixed upper-bound timing, high-priority handling, minimal nesting, a concise ISR, and avoiding long critical sections, you achieve true deterministic interrupt latency.