Event Library

An event is like a message. Multiple senders can send the message but only one subscriber can wait for and receive it.

An event is declared with 
​

and initialised by
​

To send an event, use send().

By default, Event_Id_00 is sent.

To wait for an event, use waitFor().

​By default, Event_Id_00 is waited for.

An event can manage different conditions, with OR or AND.
​
The syntax for waitFor() includes an andMask and an orMask.

• andMask AND condition, default = Event_Id_00

​The Event2 event waits for both Event_Id_02 AND Event_Id_03, listed with an addition.
​

• orMask OR condition, default = Event_Id_NONE

The Event2 event waits for any of Event_Id_02 OR Event_Id_03, listed with an addition.
​

In the example provided, there are 2 events, myEvent1 and myEvent2.

• For the simple myEvent1, the message is sent by Galaxia_Event.ino every 2 seconds and received by LED1.ino.
• For the event with conditions myEvent2, messages are sent by Event2.ino every 5 seconds and Event3.ino every 3 seconds and received by LED23.ino.

​The example uses a semaphore to manage the serial console. For an introduction to semaphore, please refer to Semaphore Library.

Only a single Task can wait for a given Event object at a time.

galaxia_event.zip
File Size:	8 kb
File Type:	zip

Download File

---

Simple Event

The event Event1 with Event_Id_01 is sent by Event1.ino every 2 seconds.

​

On the loop() function of the LED1.ino sketch, the message with Event_Id_01 is waited for and received.

​

The result is shown on the right.

The green LED state is changed each time Event1 with Event_Id_01 is sent.

​

AND Condition for Events 

Events can carry conditions, and wait for all the conditions to be met (AND condition), or wait for any of a list of conditions is sent (OR condition).
​

On the loop() function of the LED23.ino sketch, uncomment

• Condition Event_Id_02 of Event2 is sent by Event2.ino every 5 seconds.

​

• Condition Event_Id_03 of Event2 is sent by Event3.ino every 3 seconds.

​

The result is shown on the right.
​
The green LED state is changed when both Event_Id_02 and Event_Id_03 are sent.

​

OR Condition for Events

On the loop() function of the LED23.ino sketch, uncomment

As before, condition Event_Id_02 is sent by Event2.ino every 5 seconds and condition Event_Id_03 of Event2 is sent by Event3.ino. every 3 seconds.

​

The result is shown on the right.
​
The green LED state is changed when either Event_Id_02 or Event_Id_03 is sent first.

​

Conclusion

The events offer an elegant solution to send messages with conditions to trigger actions. When the program is waiting for an event, it enters low power mode.
​

Only a single Task can wait for a given Event object at a time

Posted: Apr 08, 2016