Embedded Programming with Modern C++ Cookbook

Guidelines for Real-Time Systems

Real-time systems are a class of embedded systems where the time of reaction is critical. The consequences of not reacting in time vary between different applications. Based on severity, real-time systems are classified as follows:

• Hard real time: Missing a deadline is not acceptable and considered a system failure. These are usually mission-critical systems in airplanes, cars, and power plants.
• Firm real time: Missing a deadline is acceptable in rare cases. The usefulness of the result is zero after the deadline. Think about a live streaming service. A video frame delivered too late can only be discarded. This is tolerable provided it happens infrequently.
• Soft real time: Missing a deadline is acceptable. ...