HW 22: Chapter 21

 21.4: What are the commonly used architectural patterns in real-time systems and when are they used? 


From book:
1. Observe and React
This pattern is used when a set of sensors are routinely monitored and displayed. When the sensors show that some event has occurred (e.g., an incoming call on a cell phone), the system reacts by initiating a process to handle that event. 

2. Environmental Control 

This pattern is used when a system includes sensors, which provide information about the environment and actuators that can change the environment. In response to environmental changes detected by the sensor, control signals are sent to the system actuators. 

3. Process Pipeline 

This pattern is used when data has to be transformed from one representation to another before it can be processed. The transformation is implemented as a sequence of processing steps, which may be carried out concurrently. This allows for very fast data processing, because a separate core or processor can execute each transformation.

Explanation:
1. This one is very straightforward -- it checks for stimuli and then reacts based on the condition given by the event.  It is used in monitoring systems and real-time systems based on detection.

2. The environmental control also uses sensory input, but it also has system actuators which can manage information given by observing events.  Rather than just detect changes in the environment, it actually collects and analyses data from the environment.  This is the most widely used pattern, used in things such as cars.

3. This is useful for transmitting data.  It can collect analog data from the environment and digitize it for processing, or visa versa.  It can do this quickly because it can be processed in independent processes.  This used in things like radios and high-speed data acquisition tools used in science. 

All of these patterns can be combined depending on the requirements of the system.

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