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 DATAFLOW COMMUNICATION PATTERN
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Four periodic threads.
Three of them exchange information via data ports.

The timing behavior differs depending on the value of the 
standard Timing property of the port connections.
- Sampling mode (default): the dataflow does not impact 
the scheduling (asynchronous dataflow).
- Immediate mode: scheduling follows the dataflow sequence 
(synchronous dataflow)
- Delayed mode: same as Immediate with one period offset

The functional behavior of each thread is specified by a 
standard Behavior_Specification subclause. 
The value of the output data port is set to the square of 
the value of the input data port.

The initial value of the input data port of the first thread 
is specified by a simulation scenario, and probes show the 
dataflow value at each stage.