A PalmPilot® is an embedded device whose goal is to operate in real time. When you browse for an appointment or phone number, you expect the device to respond to stylus taps in a timely manner. However, if a particular stylus tap requires several seconds to respond rather than the fraction of a second normally required, nothing catastrophic will occur. The PalmPilot® is an example of a “soft real-time” embedded device. The term “soft” indicates that there is some flexibility in the real-time requirement.

All of the following are all examples of “hard real-time” applications. ADI technology is used in the development of “hard real-time” systems, such as those in the list below.

• A Full Authority Digital Engine Controller (FADEC) controls the activities of an aircraft jet engine. The FADEC design mandates particular timing requirements. For example, if the FADEC senses that a turbine drive shaft has broken, then the FADEC MUST respond with a damage mitigating action in a predetermined time.
  
  
• Fly-by-wire flight controls use electronic signals to measure a pilot’s yolk or side-stick motions and to control the aircraft’s control surfaces. The fly-by-wire flight control system MUST transmit the pilot’s intentions at a predetermined frequency. If the fly-by-wire system cannot communicate information with sufficient frequency, the aircraft can become instable --resulting in a crash.
  
  
• Unmanned Aerial Vehicle (UAV) control systems are used in advanced military programs such as the Future Combat Systems (FCS). They rely on sophisticated piloting control algorithms to keep the unmanned aircraft in flight, on target, and at a required altitude. The embedded control systems on the UAV are given a defined slice of time to execute these piloting control algorithms. If the embedded system falls behind in executing these algorithms, the UAV may become unstable and fall off course, diverge from the desired altitude, or even crash.
  

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