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What are Soft and Hard Real-Time Applications?

The argument could be made that your iPhone or your Andriod phone is an electronic 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 your finger gestures in a timely manner. However, if a particular gesture requires several seconds to respond rather than the fraction of a second normally required, nothing catastrophic will occur. You may be a little annoyed but you’ll assume something important is going on behind the scenes.  Perhaps you’ll shut down some apps that might be stealing computational power in the background.  This type of device 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.
  • The fly-by-wire Flight Control Computer (FCC) uses electronic signals to measure the pilot control motions and to control the aircraft’s control surfaces. The FCC must transmit the pilot’s intentions at a predetermined frequency. If the fly-by-wire system cannot communicate information with sufficient determinism, the aircraft can become unstable — resulting in a crash.
  • A Dynamic Positioning System (DPS) found in a marine vessel or offshore drilling platform provides capability to automatically maintain a position or heading using propellers, rudders, and thrusters.  The DPS uses a real-time positioning control system interfaced with sensor systems, position reference systems, and thruster and power interfaces to perform its task.  If the DPS cannot execute its control strategy at the predetermined frequency then positional or trajectional stability may be lost which could result in damage to equipment, injury, or loss of life.

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