Which statement best describes latency in an event-driven control system?

• A. Latency is the time required to poll sensors.
• B. Latency is the maximum time allowed for a response.
• C. Latency is the delay from event to response.
• D. Latency is the duration of a mission.

Answer: (C)

Latency is the delay from event to response in an event-driven control system. It measures how long it takes for something happening (like a sensor input changing or an interrupt firing) to produce a corresponding action (like sending a command to an actuator). This focus on actual reaction time is what determines real-time responsiveness: the shorter the latency, the quicker the system reacts to changes.

This isn’t the time spent polling sensors (that describes a polling approach rather than event-driven), and it isn’t the maximum time allowed for a response (that would be a deadline or worst-case timing constraint). It also isn’t the total duration of a mission. For example, if a sensor event occurs at time zero and the actuator command is issued 8 milliseconds later, the latency is 8 milliseconds.