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UserAllocatedEvent

The UserAllocatedEvent class provides APIs to create and configure static events. The advantage in using UserAllocatedEvent instead of Event is UserAllocatedEvent embeds all underlying event data and doesn't require any memory allocation while posting and dispatching to the EventQueue.

This class includes the following APIs:

  • delay and period to configure event timings.
  • call and try_call to post an event to the underlying EventQueue.
  • call_on and try_call_on to bind and post an event to the EventQueue as a function argument.
  • cancel to cancel the most recently posted event.

Because the UserAllocatedEvent holds event data, you can post only one event object to it at a time. This means that if the event object has to be reused, the previous dispatch has to finish or the event has to be canceled. You can use the try_call API to sample the event state. This call tries to post an event and returns false with no action until the previous dispatching finishes.

The UserAllocatedEvent class is thread safe. The call, try_call and cancel APIs are IRQ safe.

UserAllocatedEvent class reference

Static EventQueue example: posting user allocated events to the queue

This example demonstrates how you can instantiate, configure and post events:

/*
* Copyright (c) 2019 ARM Limited. All rights reserved.
* SPDX-License-Identifier: Apache-2.0
* Licensed under the Apache License, Version 2.0 (the License); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an AS IS BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

#include "mbed.h"


// Creates static event queue
static EventQueue queue(0);

void handler(int count);

// Creates events for later bound
auto event1 = make_user_allocated_event(handler, 1);
auto event2 = make_user_allocated_event(handler, 2);

// Creates event bound to the specified event queue
auto event3 = queue.make_user_allocated_event(handler, 3);
auto event4 = queue.make_user_allocated_event(handler, 4);
 
void handler(int count) {
    printf("UserAllocatedEvent = %d \n", count);
    return;
}
 
void post_events(void) 
{
    // Single instance of user allocated event can be posted only once.
    // Event can be posted again if the previous dispatch has finished or event has been canceled.

    // bind & post
    event1.call_on(&queue);

    // event cannot be posted again until dispatched or canceled
    bool post_succeed = event1.try_call();
    assert(!post_succeed);

    queue.cancel(&event1);

    // try to post
    post_succeed = event1.try_call();
    assert(post_succeed);

    // bind & post
    post_succeed = event2.try_call_on(&queue);
    assert(post_succeed);

    // post
    event3.call();

    // post
    event4();
}

int main() 
{
    printf("*** start ***\n");
    Thread event_thread;

    // The event can be manually configured for special timing requirements
    // specified in milliseconds
    // Starting delay - 100 msec
    // Delay between each event - 200msec
    event1.delay(100);
    event1.period(200);
    event2.delay(100);
    event2.period(200);
    event3.delay(100);
    event3.period(200);
    event4.delay(100);
    event4.period(200);

    event_thread.start(callback(post_events));

    // Posted events are dispatched in the context of the queue's dispatch function
    queue.dispatch(400);        // Dispatch time - 400msec
    // 400 msec - Only 2 set of events will be dispatched as period is 200 msec

    event_thread.join();
}

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