L3

Question 1

Software design: Regular vs. real-time software - Static/dynamic structure

Answer 1

Regular: Object and data structures created/destroyed dynamicaly

Real-time: Static structures created at system initialization

Question 2

Software design: Regular vs. real-time software - Control flow

Answer 2

Regular: Complex, implicit and data-dependent control flow

Real-time: Simple, explicit and deterministic control flow

Question 3

Software design: Regular vs. real-time software - Concurrency

Answer 3

Regular: Fair interleaved execution - optimized for average case

Real-time: Predictable (priority-based) scheduler - predictable worst case

Question 4

When can multiple tasks use the same sensor?

Answer 4

• If reading from a sensor is fast and simple, tasks can share it
• If reading form the sensor is complicated or takes a long time, a dedicated task might be more appropriate

Question 5

Separating common computations?

Answer 5

• If activities need the same computed data, computing it in a separate task can be more efficient and easier to maintain

Question 6

Identifying tasks - Decomposing functions into tasks

Answer 6

• avoid overhead (at runtime and in analysis) of too many tasks
• consider separation of functions, especially those with different timing constraints
• consider the joint use of sensors, actuators or intermediate results

Question 7

A single task is not always a good solution.

Answer 7

• Handling many functions in a single task, at the frequency required by the strictest timing requirements, is often not possible
• Even if it is possible, we often waste resources with this solution.

Question 8

When can multiple tasks control the same actuator?

Answer 8

• As for sensors, is writing to the actuator fast and simple?
• Additionally, will the different functions interfere with each other?

Question 9

Assigning task periods

Answer 9

Periodicity constraints
- use a task period shorter or equal to the periodicity value

Latest response time constraints
- Note: Period t does not satisfy “react within t times units”
- however, any period shorter or equal to t/2 does!

Separation, periodicity with output jitter, earliest response time
- these cant be satisfied in a good way by just period assignment

All tasks involved in a function must be considered
- giving just one task a short period does not improve the overall timing