takashi kadono / Mbed OS Nucleo_446

Important changes to repositories hosted on mbed.com

Mbed hosted mercurial repositories are deprecated and are due to be permanently deleted in July 2026.

To keep a copy of this software download the repository Zip archive or clone locally using Mercurial.

It is also possible to export all your personal repositories from the account settings page.

Dependencies:   ssd1331

mbed-os/events/README.md@3:f3764f852aa8, 2018-10-11 (annotated)

Committer:
kadonotakashi
Date:
Thu Oct 11 02:27:46 2018 +0000
Revision:
3:f3764f852aa8
Parent:
0:8fdf9a60065b 
Nucreo 446 + SSD1331 test version;

Who changed what in which revision?

UserRevisionLine numberNew contents of line
kadonotakashi 0:8fdf9a60065b 1 ## The mbed-events library ##
kadonotakashi 0:8fdf9a60065b 2
kadonotakashi 0:8fdf9a60065b 3 The mbed-events library provides a flexible queue for scheduling events.
kadonotakashi 0:8fdf9a60065b 4
kadonotakashi 0:8fdf9a60065b 5 ``` cpp
kadonotakashi 0:8fdf9a60065b 6 #include "mbed_events.h"
kadonotakashi 0:8fdf9a60065b 7 #include <stdio.h>
kadonotakashi 0:8fdf9a60065b 8
kadonotakashi 0:8fdf9a60065b 9 int main() {
kadonotakashi 0:8fdf9a60065b 10 // creates a queue with the default size
kadonotakashi 0:8fdf9a60065b 11 EventQueue queue;
kadonotakashi 0:8fdf9a60065b 12
kadonotakashi 0:8fdf9a60065b 13 // events are simple callbacks
kadonotakashi 0:8fdf9a60065b 14 queue.call(printf, "called immediately\n");
kadonotakashi 0:8fdf9a60065b 15 queue.call_in(2000, printf, "called in 2 seconds\n");
kadonotakashi 0:8fdf9a60065b 16 queue.call_every(1000, printf, "called every 1 seconds\n");
kadonotakashi 0:8fdf9a60065b 17
kadonotakashi 0:8fdf9a60065b 18 // events are executed by the dispatch method
kadonotakashi 0:8fdf9a60065b 19 queue.dispatch();
kadonotakashi 0:8fdf9a60065b 20 }
kadonotakashi 0:8fdf9a60065b 21 ```
kadonotakashi 0:8fdf9a60065b 22
kadonotakashi 0:8fdf9a60065b 23 The mbed-events library can be used as a normal event loop, or it can be
kadonotakashi 0:8fdf9a60065b 24 backgrounded on a single hardware timer or even another event loop. It is
kadonotakashi 0:8fdf9a60065b 25 both thread and irq safe, and provides functions for easily composing
kadonotakashi 0:8fdf9a60065b 26 independent event queues.
kadonotakashi 0:8fdf9a60065b 27
kadonotakashi 0:8fdf9a60065b 28 The mbed-events library can act as a drop-in scheduler, provide synchronization
kadonotakashi 0:8fdf9a60065b 29 between multiple threads, or just act as a mechanism for moving events out of
kadonotakashi 0:8fdf9a60065b 30 interrupt contexts.
kadonotakashi 0:8fdf9a60065b 31
kadonotakashi 0:8fdf9a60065b 32 ### Usage ###
kadonotakashi 0:8fdf9a60065b 33
kadonotakashi 0:8fdf9a60065b 34 The core of the mbed-events library is the [EventQueue](EventQueue.h) class,
kadonotakashi 0:8fdf9a60065b 35 which represents a single event queue. The `EventQueue::dispatch` function
kadonotakashi 0:8fdf9a60065b 36 runs the queue, providing the context for executing events.
kadonotakashi 0:8fdf9a60065b 37
kadonotakashi 0:8fdf9a60065b 38 ``` cpp
kadonotakashi 0:8fdf9a60065b 39 // Creates an event queue enough buffer space for 32 Callbacks. This
kadonotakashi 0:8fdf9a60065b 40 // is the default if no argument was provided. Alternatively the size
kadonotakashi 0:8fdf9a60065b 41 // can just be specified in bytes.
kadonotakashi 0:8fdf9a60065b 42 EventQueue queue(32*EVENTS_EVENT_SIZE);
kadonotakashi 0:8fdf9a60065b 43
kadonotakashi 0:8fdf9a60065b 44 // Events can be posted to the underlying event queue with dynamic
kadonotakashi 0:8fdf9a60065b 45 // context allocated from the specified buffer
kadonotakashi 0:8fdf9a60065b 46 queue.call(printf, "hello %d %d %d %d\n", 1, 2, 3, 4);
kadonotakashi 0:8fdf9a60065b 47 queue.call(&serial, &Serial::printf, "hi\n");
kadonotakashi 0:8fdf9a60065b 48
kadonotakashi 0:8fdf9a60065b 49 // The dispatch function provides the context for the running the queue
kadonotakashi 0:8fdf9a60065b 50 // and can take a millisecond timeout to run for a fixed time or to just
kadonotakashi 0:8fdf9a60065b 51 // dispatch any pending events
kadonotakashi 0:8fdf9a60065b 52 queue.dispatch();
kadonotakashi 0:8fdf9a60065b 53 ```
kadonotakashi 0:8fdf9a60065b 54
kadonotakashi 0:8fdf9a60065b 55 The EventQueue class provides several call functions for posting events
kadonotakashi 0:8fdf9a60065b 56 to the underlying event queue. The call functions are thread and irq safe,
kadonotakashi 0:8fdf9a60065b 57 don't need the underlying loop to be running, and provide an easy mechanism
kadonotakashi 0:8fdf9a60065b 58 for moving events out of interrupt contexts.
kadonotakashi 0:8fdf9a60065b 59
kadonotakashi 0:8fdf9a60065b 60 ``` cpp
kadonotakashi 0:8fdf9a60065b 61 // Simple call function registers events to be called as soon as possible
kadonotakashi 0:8fdf9a60065b 62 queue.call(doit);
kadonotakashi 0:8fdf9a60065b 63 queue.call(printf, "called immediately\n");
kadonotakashi 0:8fdf9a60065b 64
kadonotakashi 0:8fdf9a60065b 65 // The call_in function registers events to be called after a delay
kadonotakashi 0:8fdf9a60065b 66 // specified in milliseconds
kadonotakashi 0:8fdf9a60065b 67 queue.call_in(2000, doit_in_two_seconds);
kadonotakashi 0:8fdf9a60065b 68 queue.call_in(300, printf, "called in 0.3 seconds\n");
kadonotakashi 0:8fdf9a60065b 69
kadonotakashi 0:8fdf9a60065b 70 // The call_every function registers events to be called repeatedly
kadonotakashi 0:8fdf9a60065b 71 // with a period specified in milliseconds
kadonotakashi 0:8fdf9a60065b 72 queue.call_every(2000, doit_every_two_seconds);
kadonotakashi 0:8fdf9a60065b 73 queue.call_every(400, printf, "called every 0.4 seconds\n");
kadonotakashi 0:8fdf9a60065b 74 ```
kadonotakashi 0:8fdf9a60065b 75
kadonotakashi 0:8fdf9a60065b 76 The call functions return an id that uniquely represents the event in the
kadonotakashi 0:8fdf9a60065b 77 the event queue. This id can be passed to `EventQueue::cancel` to cancel
kadonotakashi 0:8fdf9a60065b 78 an in-flight event.
kadonotakashi 0:8fdf9a60065b 79
kadonotakashi 0:8fdf9a60065b 80 ``` cpp
kadonotakashi 0:8fdf9a60065b 81 // The event id uniquely represents the event in the queue
kadonotakashi 0:8fdf9a60065b 82 int id = queue.call_in(100, printf, "will this work?\n");
kadonotakashi 0:8fdf9a60065b 83
kadonotakashi 0:8fdf9a60065b 84 // If there was not enough memory necessary to allocate the event,
kadonotakashi 0:8fdf9a60065b 85 // an id of 0 is returned from the call functions
kadonotakashi 0:8fdf9a60065b 86 if (id) {
kadonotakashi 0:8fdf9a60065b 87 error("oh no!");
kadonotakashi 0:8fdf9a60065b 88 }
kadonotakashi 0:8fdf9a60065b 89
kadonotakashi 0:8fdf9a60065b 90 // Events can be cancelled as long as they have not been dispatched. If the
kadonotakashi 0:8fdf9a60065b 91 // event has already expired, cancel has no side-effects.
kadonotakashi 0:8fdf9a60065b 92 queue.cancel(id);
kadonotakashi 0:8fdf9a60065b 93 ```
kadonotakashi 0:8fdf9a60065b 94
kadonotakashi 0:8fdf9a60065b 95 For a more fine-grain control of event dispatch, the `Event` class can be
kadonotakashi 0:8fdf9a60065b 96 manually instantiated and configured. An `Event` represents an event as
kadonotakashi 0:8fdf9a60065b 97 a C++ style function object and can be directly passed to other APIs that
kadonotakashi 0:8fdf9a60065b 98 expect a callback.
kadonotakashi 0:8fdf9a60065b 99
kadonotakashi 0:8fdf9a60065b 100 ``` cpp
kadonotakashi 0:8fdf9a60065b 101 // Creates an event bound to the specified event queue
kadonotakashi 0:8fdf9a60065b 102 EventQueue queue;
kadonotakashi 0:8fdf9a60065b 103 Event<void()> event(&queue, doit);
kadonotakashi 0:8fdf9a60065b 104
kadonotakashi 0:8fdf9a60065b 105 // The event can be manually configured for special timing requirements
kadonotakashi 0:8fdf9a60065b 106 // specified in milliseconds
kadonotakashi 0:8fdf9a60065b 107 event.delay(10);
kadonotakashi 0:8fdf9a60065b 108 event.period(10000);
kadonotakashi 0:8fdf9a60065b 109
kadonotakashi 0:8fdf9a60065b 110 // Posted events are dispatched in the context of the queue's
kadonotakashi 0:8fdf9a60065b 111 // dispatch function
kadonotakashi 0:8fdf9a60065b 112 queue.dispatch();
kadonotakashi 0:8fdf9a60065b 113
kadonotakashi 0:8fdf9a60065b 114 // Events can also pass arguments to the underlying callback when both
kadonotakashi 0:8fdf9a60065b 115 // initially constructed and posted.
kadonotakashi 0:8fdf9a60065b 116 Event<void(int, int)> event(&queue, printf, "received %d and %d\n");
kadonotakashi 0:8fdf9a60065b 117
kadonotakashi 0:8fdf9a60065b 118 // Events can be posted multiple times and enqueue gracefully until
kadonotakashi 0:8fdf9a60065b 119 // the dispatch function is called.
kadonotakashi 0:8fdf9a60065b 120 event.post(1, 2);
kadonotakashi 0:8fdf9a60065b 121 event.post(3, 4);
kadonotakashi 0:8fdf9a60065b 122 event.post(5, 6);
kadonotakashi 0:8fdf9a60065b 123
kadonotakashi 0:8fdf9a60065b 124 queue.dispatch();
kadonotakashi 0:8fdf9a60065b 125 ```
kadonotakashi 0:8fdf9a60065b 126
kadonotakashi 0:8fdf9a60065b 127 Event queues easily align with module boundaries, where internal state can
kadonotakashi 0:8fdf9a60065b 128 be implicitly synchronized through event dispatch. Multiple modules can
kadonotakashi 0:8fdf9a60065b 129 use independent event queues, but still be composed through the
kadonotakashi 0:8fdf9a60065b 130 `EventQueue::chain` function.
kadonotakashi 0:8fdf9a60065b 131
kadonotakashi 0:8fdf9a60065b 132 ``` cpp
kadonotakashi 0:8fdf9a60065b 133 // Create some event queues with pending events
kadonotakashi 0:8fdf9a60065b 134 EventQueue a;
kadonotakashi 0:8fdf9a60065b 135 a.call(printf, "hello from a!\n");
kadonotakashi 0:8fdf9a60065b 136
kadonotakashi 0:8fdf9a60065b 137 EventQueue b;
kadonotakashi 0:8fdf9a60065b 138 b.call(printf, "hello from b!\n");
kadonotakashi 0:8fdf9a60065b 139
kadonotakashi 0:8fdf9a60065b 140 EventQueue c;
kadonotakashi 0:8fdf9a60065b 141 c.call(printf, "hello from c!\n");
kadonotakashi 0:8fdf9a60065b 142
kadonotakashi 0:8fdf9a60065b 143 // Chain c and b onto a's event queue. Both c and b will be dispatched
kadonotakashi 0:8fdf9a60065b 144 // in the context of a's dispatch function.
kadonotakashi 0:8fdf9a60065b 145 c.chain(&a);
kadonotakashi 0:8fdf9a60065b 146 b.chain(&a);
kadonotakashi 0:8fdf9a60065b 147
kadonotakashi 0:8fdf9a60065b 148 // Dispatching a will in turn dispatch b and c, printing hello from
kadonotakashi 0:8fdf9a60065b 149 // all three queues
kadonotakashi 0:8fdf9a60065b 150 a.dispatch();
kadonotakashi 0:8fdf9a60065b 151 ```
kadonotakashi 0:8fdf9a60065b 152
kadonotakashi 0:8fdf9a60065b 153