Marco Zecchini / Mbed OS Example_RTOS

Rtos API example

mbed-os/events/README.md@0:9fca2b23d0ba, 2019-02-23 (annotated)

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marcozecchini
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marcozecchini 0:9fca2b23d0ba 1 ## The mbed-events library ##
marcozecchini 0:9fca2b23d0ba 2
marcozecchini 0:9fca2b23d0ba 3 The mbed-events library provides a flexible queue for scheduling events.
marcozecchini 0:9fca2b23d0ba 4
marcozecchini 0:9fca2b23d0ba 5 ``` cpp
marcozecchini 0:9fca2b23d0ba 6 #include "mbed_events.h"
marcozecchini 0:9fca2b23d0ba 7 #include <stdio.h>
marcozecchini 0:9fca2b23d0ba 8
marcozecchini 0:9fca2b23d0ba 9 int main() {
marcozecchini 0:9fca2b23d0ba 10 // creates a queue with the default size
marcozecchini 0:9fca2b23d0ba 11 EventQueue queue;
marcozecchini 0:9fca2b23d0ba 12
marcozecchini 0:9fca2b23d0ba 13 // events are simple callbacks
marcozecchini 0:9fca2b23d0ba 14 queue.call(printf, "called immediately\n");
marcozecchini 0:9fca2b23d0ba 15 queue.call_in(2000, printf, "called in 2 seconds\n");
marcozecchini 0:9fca2b23d0ba 16 queue.call_every(1000, printf, "called every 1 seconds\n");
marcozecchini 0:9fca2b23d0ba 17
marcozecchini 0:9fca2b23d0ba 18 // events are executed by the dispatch method
marcozecchini 0:9fca2b23d0ba 19 queue.dispatch();
marcozecchini 0:9fca2b23d0ba 20 }
marcozecchini 0:9fca2b23d0ba 21 ```
marcozecchini 0:9fca2b23d0ba 22
marcozecchini 0:9fca2b23d0ba 23 The mbed-events library can be used as a normal event loop, or it can be
marcozecchini 0:9fca2b23d0ba 24 backgrounded on a single hardware timer or even another event loop. It is
marcozecchini 0:9fca2b23d0ba 25 both thread and irq safe, and provides functions for easily composing
marcozecchini 0:9fca2b23d0ba 26 independent event queues.
marcozecchini 0:9fca2b23d0ba 27
marcozecchini 0:9fca2b23d0ba 28 The mbed-events library can act as a drop-in scheduler, provide synchronization
marcozecchini 0:9fca2b23d0ba 29 between multiple threads, or just act as a mechanism for moving events out of
marcozecchini 0:9fca2b23d0ba 30 interrupt contexts.
marcozecchini 0:9fca2b23d0ba 31
marcozecchini 0:9fca2b23d0ba 32 ### Usage ###
marcozecchini 0:9fca2b23d0ba 33
marcozecchini 0:9fca2b23d0ba 34 The core of the mbed-events library is the [EventQueue](EventQueue.h) class,
marcozecchini 0:9fca2b23d0ba 35 which represents a single event queue. The `EventQueue::dispatch` function
marcozecchini 0:9fca2b23d0ba 36 runs the queue, providing the context for executing events.
marcozecchini 0:9fca2b23d0ba 37
marcozecchini 0:9fca2b23d0ba 38 ``` cpp
marcozecchini 0:9fca2b23d0ba 39 // Creates an event queue enough buffer space for 32 Callbacks. This
marcozecchini 0:9fca2b23d0ba 40 // is the default if no argument was provided. Alternatively the size
marcozecchini 0:9fca2b23d0ba 41 // can just be specified in bytes.
marcozecchini 0:9fca2b23d0ba 42 EventQueue queue(32*EVENTS_EVENT_SIZE);
marcozecchini 0:9fca2b23d0ba 43
marcozecchini 0:9fca2b23d0ba 44 // Events can be posted to the underlying event queue with dynamic
marcozecchini 0:9fca2b23d0ba 45 // context allocated from the specified buffer
marcozecchini 0:9fca2b23d0ba 46 queue.call(printf, "hello %d %d %d %d\n", 1, 2, 3, 4);
marcozecchini 0:9fca2b23d0ba 47 queue.call(&serial, &Serial::printf, "hi\n");
marcozecchini 0:9fca2b23d0ba 48
marcozecchini 0:9fca2b23d0ba 49 // The dispatch function provides the context for the running the queue
marcozecchini 0:9fca2b23d0ba 50 // and can take a millisecond timeout to run for a fixed time or to just
marcozecchini 0:9fca2b23d0ba 51 // dispatch any pending events
marcozecchini 0:9fca2b23d0ba 52 queue.dispatch();
marcozecchini 0:9fca2b23d0ba 53 ```
marcozecchini 0:9fca2b23d0ba 54
marcozecchini 0:9fca2b23d0ba 55 The EventQueue class provides several call functions for posting events
marcozecchini 0:9fca2b23d0ba 56 to the underlying event queue. The call functions are thread and irq safe,
marcozecchini 0:9fca2b23d0ba 57 don't need the underlying loop to be running, and provide an easy mechanism
marcozecchini 0:9fca2b23d0ba 58 for moving events out of interrupt contexts.
marcozecchini 0:9fca2b23d0ba 59
marcozecchini 0:9fca2b23d0ba 60 ``` cpp
marcozecchini 0:9fca2b23d0ba 61 // Simple call function registers events to be called as soon as possible
marcozecchini 0:9fca2b23d0ba 62 queue.call(doit);
marcozecchini 0:9fca2b23d0ba 63 queue.call(printf, "called immediately\n");
marcozecchini 0:9fca2b23d0ba 64
marcozecchini 0:9fca2b23d0ba 65 // The call_in function registers events to be called after a delay
marcozecchini 0:9fca2b23d0ba 66 // specified in milliseconds
marcozecchini 0:9fca2b23d0ba 67 queue.call_in(2000, doit_in_two_seconds);
marcozecchini 0:9fca2b23d0ba 68 queue.call_in(300, printf, "called in 0.3 seconds\n");
marcozecchini 0:9fca2b23d0ba 69
marcozecchini 0:9fca2b23d0ba 70 // The call_every function registers events to be called repeatedly
marcozecchini 0:9fca2b23d0ba 71 // with a period specified in milliseconds
marcozecchini 0:9fca2b23d0ba 72 queue.call_every(2000, doit_every_two_seconds);
marcozecchini 0:9fca2b23d0ba 73 queue.call_every(400, printf, "called every 0.4 seconds\n");
marcozecchini 0:9fca2b23d0ba 74 ```
marcozecchini 0:9fca2b23d0ba 75
marcozecchini 0:9fca2b23d0ba 76 The call functions return an id that uniquely represents the event in the
marcozecchini 0:9fca2b23d0ba 77 the event queue. This id can be passed to `EventQueue::cancel` to cancel
marcozecchini 0:9fca2b23d0ba 78 an in-flight event.
marcozecchini 0:9fca2b23d0ba 79
marcozecchini 0:9fca2b23d0ba 80 ``` cpp
marcozecchini 0:9fca2b23d0ba 81 // The event id uniquely represents the event in the queue
marcozecchini 0:9fca2b23d0ba 82 int id = queue.call_in(100, printf, "will this work?\n");
marcozecchini 0:9fca2b23d0ba 83
marcozecchini 0:9fca2b23d0ba 84 // If there was not enough memory necessary to allocate the event,
marcozecchini 0:9fca2b23d0ba 85 // an id of 0 is returned from the call functions
marcozecchini 0:9fca2b23d0ba 86 if (id) {
marcozecchini 0:9fca2b23d0ba 87 error("oh no!");
marcozecchini 0:9fca2b23d0ba 88 }
marcozecchini 0:9fca2b23d0ba 89
marcozecchini 0:9fca2b23d0ba 90 // Events can be cancelled as long as they have not been dispatched. If the
marcozecchini 0:9fca2b23d0ba 91 // event has already expired, cancel has no side-effects.
marcozecchini 0:9fca2b23d0ba 92 queue.cancel(id);
marcozecchini 0:9fca2b23d0ba 93 ```
marcozecchini 0:9fca2b23d0ba 94
marcozecchini 0:9fca2b23d0ba 95 For a more fine-grain control of event dispatch, the `Event` class can be
marcozecchini 0:9fca2b23d0ba 96 manually instantiated and configured. An `Event` represents an event as
marcozecchini 0:9fca2b23d0ba 97 a C++ style function object and can be directly passed to other APIs that
marcozecchini 0:9fca2b23d0ba 98 expect a callback.
marcozecchini 0:9fca2b23d0ba 99
marcozecchini 0:9fca2b23d0ba 100 ``` cpp
marcozecchini 0:9fca2b23d0ba 101 // Creates an event bound to the specified event queue
marcozecchini 0:9fca2b23d0ba 102 EventQueue queue;
marcozecchini 0:9fca2b23d0ba 103 Event<void()> event(&queue, doit);
marcozecchini 0:9fca2b23d0ba 104
marcozecchini 0:9fca2b23d0ba 105 // The event can be manually configured for special timing requirements
marcozecchini 0:9fca2b23d0ba 106 // specified in milliseconds
marcozecchini 0:9fca2b23d0ba 107 event.delay(10);
marcozecchini 0:9fca2b23d0ba 108 event.period(10000);
marcozecchini 0:9fca2b23d0ba 109
marcozecchini 0:9fca2b23d0ba 110 // Posted events are dispatched in the context of the queue's
marcozecchini 0:9fca2b23d0ba 111 // dispatch function
marcozecchini 0:9fca2b23d0ba 112 queue.dispatch();
marcozecchini 0:9fca2b23d0ba 113
marcozecchini 0:9fca2b23d0ba 114 // Events can also pass arguments to the underlying callback when both
marcozecchini 0:9fca2b23d0ba 115 // initially constructed and posted.
marcozecchini 0:9fca2b23d0ba 116 Event<void(int, int)> event(&queue, printf, "recieved %d and %d\n");
marcozecchini 0:9fca2b23d0ba 117
marcozecchini 0:9fca2b23d0ba 118 // Events can be posted multiple times and enqueue gracefully until
marcozecchini 0:9fca2b23d0ba 119 // the dispatch function is called.
marcozecchini 0:9fca2b23d0ba 120 event.post(1, 2);
marcozecchini 0:9fca2b23d0ba 121 event.post(3, 4);
marcozecchini 0:9fca2b23d0ba 122 event.post(5, 6);
marcozecchini 0:9fca2b23d0ba 123
marcozecchini 0:9fca2b23d0ba 124 queue.dispatch();
marcozecchini 0:9fca2b23d0ba 125 ```
marcozecchini 0:9fca2b23d0ba 126
marcozecchini 0:9fca2b23d0ba 127 Event queues easily align with module boundaries, where internal state can
marcozecchini 0:9fca2b23d0ba 128 be implicitly synchronized through event dispatch. Multiple modules can
marcozecchini 0:9fca2b23d0ba 129 use independent event queues, but still be composed through the
marcozecchini 0:9fca2b23d0ba 130 `EventQueue::chain` function.
marcozecchini 0:9fca2b23d0ba 131
marcozecchini 0:9fca2b23d0ba 132 ``` cpp
marcozecchini 0:9fca2b23d0ba 133 // Create some event queues with pending events
marcozecchini 0:9fca2b23d0ba 134 EventQueue a;
marcozecchini 0:9fca2b23d0ba 135 a.call(printf, "hello from a!\n");
marcozecchini 0:9fca2b23d0ba 136
marcozecchini 0:9fca2b23d0ba 137 EventQueue b;
marcozecchini 0:9fca2b23d0ba 138 b.call(printf, "hello from b!\n");
marcozecchini 0:9fca2b23d0ba 139
marcozecchini 0:9fca2b23d0ba 140 EventQueue c;
marcozecchini 0:9fca2b23d0ba 141 c.call(printf, "hello from c!\n");
marcozecchini 0:9fca2b23d0ba 142
marcozecchini 0:9fca2b23d0ba 143 // Chain c and b onto a's event queue. Both c and b will be dispatched
marcozecchini 0:9fca2b23d0ba 144 // in the context of a's dispatch function.
marcozecchini 0:9fca2b23d0ba 145 c.chain(&a);
marcozecchini 0:9fca2b23d0ba 146 b.chain(&a);
marcozecchini 0:9fca2b23d0ba 147
marcozecchini 0:9fca2b23d0ba 148 // Dispatching a will in turn dispatch b and c, printing hello from
marcozecchini 0:9fca2b23d0ba 149 // all three queues
marcozecchini 0:9fca2b23d0ba 150 a.dispatch();
marcozecchini 0:9fca2b23d0ba 151 ```
marcozecchini 0:9fca2b23d0ba 152
marcozecchini 0:9fca2b23d0ba 153