Communication between DEVSLib models
The interfaces for model communication are arranged in the package Interfaces.
Input Ports
The inPort model represents the interface for input messages.
It contains two variables, the event and the queue.
The event represents that a new message or messages have been received at the port.
It is a flow variable because multiple models can send messages to the same port, so the total number of messages must be summed up.
The queue represents a reference to the storage space for the incoming messages.
Output Ports
The outPort model represents the interface for output messages.
It contains two variables, the event and the queue.
The event represents that a new message or messages have been sent through the port.
It is a flow variable because multiple models can send messages to the same port, so the total number of messages must be summed up.
The queue represents a reference to the storage space for the outgoing messages.
Messages
The communication between models is performed as a message passing mechanism.
The output function of one model generates a message that is sent to the input port of a connected model.
The model that receives the message executes an external transition.
Due to the restrictions of the Modelica language, this message pasing mechanism has been implemented using external functions that store messages in dynamic memory.
Only references to the messages and the data structures that store the messages (queues, lists, etc) are stored in the Modelica variables.
The implementation of these external functions is included in the file events.c.
Message Management Functions
Several functions for message and queue management have been included in the library:
- sendEvent, sends a message to a queue (message is stored a the end of the queue).
- sendEventLIFO, sends a message to a queue (message is stored at the beginning of the queue).
- sendEventLVF, sends a message to a queue (message is stored by increasing 'value').
- sendEventHVF, sends a message to a queue (message is stored by decreasing 'value').
- readEvent, reads a message from the 'position' of the queue.
- getEvent, reads a message from the 'position' of the queue.
- numEvents, returns the number of messages in the queue.
- eventOrder, returns the ordering value for the message in that 'position' of the queue.
- CreateQueue, creates a new queue for messages.
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.DESLib.DEVSLib.SRC.DevelopersGuide.Communication