Interrupt Latency

1. Interrupt Latency and Response
of Tasks as Performance Metrics
Understanding Key Performance
Indicators in Real-Time and
Embedded Systems

2. Why Performance Metrics Matter
in Real-Time Systems
• Ensures time-critical operations are executed on time
• Key metrics: Interrupt Latency and Task Response Time
• Relevant in systems like automotive, aerospace, robotics, and healthcare

3. Definition: Interrupt Latency
• Time between interrupt request (IRQ) and start of ISR
• Includes: detection time, context switching, ISR dispatch
• Critical for real-time responsiveness

4. Key Influences on Interrupt Latency
• CPU speed and architecture
• Interrupt priority and nesting
• Interrupt masking (disabled interrupts)
• RTOS overhead and scheduler efficiency

5. Definition: Task Response Time
• Time from task readiness to task completion
• Includes waiting time, scheduling delay, and execution time
• Measures timely task completion

6. Key Influences on Task Response
Time
• Task priority and preemption
• Scheduling algorithm (FIFO, Round-Robin, Priority-Based)
• System load and number of active tasks
• Resource availability and I/O blocking

7. Comparison of the Two Metrics
• Interrupt Latency: Event to ISR start
• Task Response Time: Task ready to completion
• Measured in µs vs. ms respectively
• Latency is for reaction; Response is for completion

8. Use Cases in Industry
• Automotive: Airbags need low interrupt latency
• Medical Devices: Pacemakers require consistent response times
• Industrial Robots: Both metrics are critical