QP/C++
7.3.4
Real-Time Embedded Framework
An Event is the specification of some occurrence that may potentially have significance to the system under consideration. Upon such an occurrence, a corresponding Event (class) is instantiated, and the generated Event Instance (object) outlives the instantaneous occurrence that generated it.
Event Instances (a.k.a. Messages) are objects specifically designed for communication and synchronization within an event-driven system, such as a QP Application. Once generated, an Event Instance (a.k.a. Message) is propagated to the system, where it can trigger various Actions. These Actions might involve generating secondary Event Instances.
An Event always has information about the type of occurrence that generated the Event Instance ("what happened"), which will be called Signal in this document. Event Signals are typically enumerated constants that indicate which specific occurrence out of a set of all possible (enumerated) occurrences has generated the Event Instance.
An Event can have (optionally) associated Parameters, allowing the Event Instance to convey the quantitative information regarding that occurrence. For example, a Keystroke event generated by pressing a key on a computer keyboard might have associated parameters that carry the character scan code and the status of the Shift, Ctrl, and Alt keys.
| SRS-QP-01_00 |
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| QP Framework shall provide Event abstraction to QP Application |
| Description The QP Framework shall define a common Event abstraction, so that it can be instantiated, exchanged, and correctly interpreted by both the QP Application and QP Framework. |
| SRS-QP-01_20 |
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| Each event instance shall contain the event Signal |
| Description The event Signal carries the information about the occurrence that generated the given event instance. The Signal needs to be easily accessible to the QP Application to determine how to handle a given event. |
| SRS-QP-01_21 |
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| The dynamic range of the event signal shall be compile-time configurable |
| Description QP Framework should be compile-time configurable to allow choosing the optimal dynamic range for the event signals while minimizing the size of the event instances. The following dynamic range of event signals should be configurable: 255 signals (1 byte of memory per Signal), 64K signals (2 bytes of memory per Signal), and 4G signals (4 bytes of memory per Signal). |
| SRS-QP-01_22 |
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| QP Framework may reserve some signals for its internal use |
| Description QP Framework may need some reserved signals to implement features inside hierarchical state machines. The reserved signals shall have the lowest numerical values. |
| SRS-QP-01_23 |
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| QP Framework shall provide the lowest numerical value of signals allowed in the Application |
| Description To avoid conflicts around any reserved event signals, QP Framework shall provide the lowest numerical limit for Application-level signals. In other words, the reserved signals will have numerical values 0 .. (SIGNAL_OFFSET - 1), and the Application-level signals will have values SIGNAL_OFFSET .. SIGNAL_DYNAMIC_RANGE. |
| SRS-QP-01_30 |
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| QP Framework shall allow Application to create event instances with Parameters defined by the Application |
| Description The Event abstraction shall provide a mechanism for QP Application to define event parameters useful for the QP Application, and then to create event instances with these parameters. |
| SRS-QP-01_31 |
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| Event abstraction may contain other data items for internal event management inside QP Framework |
| Description Event management in QP Framework might require additional information to be stored inside each event instance. Please see Event Memory Management for requirements related to event management inside QP Framework. |
| SRS-QP-01_40 |
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| QP Framework may be compile-time configurable to allow customized constructor and other custom operations on event instances |
| Description When such customization is configured, QP Framework shall invoke the custom construction upon instantiation of an event. |
| SRS-QP-01_41 |
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| QP Framework may be compile-time configurable to allow customized destructor of event instances |
| Description When such customization is configured, QP Framework shall invoke the custom destructor right before recycling the event instance. |