Greg Steiert / pegasus_dev

Development mbed library for MAX32630FTHR

Dependents:   blinky_max32630fthr

events/README.md@3:1198227e6421, 2016-12-16 (annotated)

Committer:
switches
Date:
Fri Dec 16 16:27:57 2016 +0000
Revision:
3:1198227e6421
Parent:
0:5c4d7b2438d3 
Changed ADC scale for MAX32625 platforms to 1.2V full scale to match MAX32630 platforms

Who changed what in which revision?

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switches 0:5c4d7b2438d3 1 ## The mbed-events library ##
switches 0:5c4d7b2438d3 2
switches 0:5c4d7b2438d3 3 The mbed-events library provides a flexible queue for scheduling events.
switches 0:5c4d7b2438d3 4
switches 0:5c4d7b2438d3 5 ``` cpp
switches 0:5c4d7b2438d3 6 #include "mbed_events.h"
switches 0:5c4d7b2438d3 7 #include <stdio.h>
switches 0:5c4d7b2438d3 8
switches 0:5c4d7b2438d3 9 int main() {
switches 0:5c4d7b2438d3 10 // creates a queue with the default size
switches 0:5c4d7b2438d3 11 EventQueue queue;
switches 0:5c4d7b2438d3 12
switches 0:5c4d7b2438d3 13 // events are simple callbacks
switches 0:5c4d7b2438d3 14 queue.call(printf, "called immediately\n");
switches 0:5c4d7b2438d3 15 queue.call_in(2000, printf, "called in 2 seconds\n");
switches 0:5c4d7b2438d3 16 queue.call_every(1000, printf, "called every 1 seconds\n");
switches 0:5c4d7b2438d3 17
switches 0:5c4d7b2438d3 18 // events are executed by the dispatch method
switches 0:5c4d7b2438d3 19 queue.dispatch();
switches 0:5c4d7b2438d3 20 }
switches 0:5c4d7b2438d3 21 ```
switches 0:5c4d7b2438d3 22
switches 0:5c4d7b2438d3 23 The mbed-events library can be used as a normal event loop, or it can be
switches 0:5c4d7b2438d3 24 backgrounded on a single hardware timer or even another event loop. It is
switches 0:5c4d7b2438d3 25 both thread and irq safe, and provides functions for easily composing
switches 0:5c4d7b2438d3 26 independent event queues.
switches 0:5c4d7b2438d3 27
switches 0:5c4d7b2438d3 28 The mbed-events library can act as a drop-in scheduler, provide synchronization
switches 0:5c4d7b2438d3 29 between multiple threads, or just act as a mechanism for moving events out of
switches 0:5c4d7b2438d3 30 interrupt contexts.
switches 0:5c4d7b2438d3 31
switches 0:5c4d7b2438d3 32 ### Usage ###
switches 0:5c4d7b2438d3 33
switches 0:5c4d7b2438d3 34 The core of the mbed-events library is the [EventQueue](EventQueue.h) class,
switches 0:5c4d7b2438d3 35 which represents a single event queue. The `EventQueue::dispatch` function
switches 0:5c4d7b2438d3 36 runs the queue, providing the context for executing events.
switches 0:5c4d7b2438d3 37
switches 0:5c4d7b2438d3 38 ``` cpp
switches 0:5c4d7b2438d3 39 // Creates an event queue enough buffer space for 32 Callbacks. This
switches 0:5c4d7b2438d3 40 // is the default if no argument was provided. Alternatively the size
switches 0:5c4d7b2438d3 41 // can just be specified in bytes.
switches 0:5c4d7b2438d3 42 EventQueue queue(32*EVENTS_EVENT_SIZE);
switches 0:5c4d7b2438d3 43
switches 0:5c4d7b2438d3 44 // Events can be posted to the underlying event queue with dynamic
switches 0:5c4d7b2438d3 45 // context allocated from the specified buffer
switches 0:5c4d7b2438d3 46 queue.call(printf, "hello %d %d %d %d\n", 1, 2, 3, 4);
switches 0:5c4d7b2438d3 47 queue.call(&serial, &Serial::printf, "hi\n");
switches 0:5c4d7b2438d3 48
switches 0:5c4d7b2438d3 49 // The dispatch function provides the context for the running the queue
switches 0:5c4d7b2438d3 50 // and can take a millisecond timeout to run for a fixed time or to just
switches 0:5c4d7b2438d3 51 // dispatch any pending events
switches 0:5c4d7b2438d3 52 queue.dispatch();
switches 0:5c4d7b2438d3 53 ```
switches 0:5c4d7b2438d3 54
switches 0:5c4d7b2438d3 55 The EventQueue class provides several call functions for posting events
switches 0:5c4d7b2438d3 56 to the underlying event queue. The call functions are thread and irq safe,
switches 0:5c4d7b2438d3 57 don't need the underlying loop to be running, and provide an easy mechanism
switches 0:5c4d7b2438d3 58 for moving events out of interrupt contexts.
switches 0:5c4d7b2438d3 59
switches 0:5c4d7b2438d3 60 ``` cpp
switches 0:5c4d7b2438d3 61 // Simple call function registers events to be called as soon as possible
switches 0:5c4d7b2438d3 62 queue.call(doit);
switches 0:5c4d7b2438d3 63 queue.call(printf, "called immediately\n");
switches 0:5c4d7b2438d3 64
switches 0:5c4d7b2438d3 65 // The call_in function registers events to be called after a delay
switches 0:5c4d7b2438d3 66 // specified in milliseconds
switches 0:5c4d7b2438d3 67 queue.call_in(2000, doit_in_two_seconds);
switches 0:5c4d7b2438d3 68 queue.call_in(300, printf, "called in 0.3 seconds\n");
switches 0:5c4d7b2438d3 69
switches 0:5c4d7b2438d3 70 // The call_every function registers events to be called repeatedly
switches 0:5c4d7b2438d3 71 // with a period specified in milliseconds
switches 0:5c4d7b2438d3 72 queue.call_every(2000, doit_every_two_seconds);
switches 0:5c4d7b2438d3 73 queue.call_every(400, printf, "called every 0.4 seconds\n");
switches 0:5c4d7b2438d3 74 ```
switches 0:5c4d7b2438d3 75
switches 0:5c4d7b2438d3 76 The call functions return an id that uniquely represents the event in the
switches 0:5c4d7b2438d3 77 the event queue. This id can be passed to `EventQueue::cancel` to cancel
switches 0:5c4d7b2438d3 78 an in-flight event.
switches 0:5c4d7b2438d3 79
switches 0:5c4d7b2438d3 80 ``` cpp
switches 0:5c4d7b2438d3 81 // The event id uniquely represents the event in the queue
switches 0:5c4d7b2438d3 82 int id = queue.call_in(100, printf, "will this work?\n");
switches 0:5c4d7b2438d3 83
switches 0:5c4d7b2438d3 84 // If there was not enough memory necessary to allocate the event,
switches 0:5c4d7b2438d3 85 // an id of 0 is returned from the call functions
switches 0:5c4d7b2438d3 86 if (id) {
switches 0:5c4d7b2438d3 87 error("oh no!");
switches 0:5c4d7b2438d3 88 }
switches 0:5c4d7b2438d3 89
switches 0:5c4d7b2438d3 90 // Events can be cancelled as long as they have not been dispatched. If the
switches 0:5c4d7b2438d3 91 // event has already expired, cancel has no side-effects.
switches 0:5c4d7b2438d3 92 queue.cancel(id);
switches 0:5c4d7b2438d3 93 ```
switches 0:5c4d7b2438d3 94
switches 0:5c4d7b2438d3 95 For a more fine-grain control of event dispatch, the `Event` class can be
switches 0:5c4d7b2438d3 96 manually instantiated and configured. An `Event` represents an event as
switches 0:5c4d7b2438d3 97 a C++ style function object and can be directly passed to other APIs that
switches 0:5c4d7b2438d3 98 expect a callback.
switches 0:5c4d7b2438d3 99
switches 0:5c4d7b2438d3 100 ``` cpp
switches 0:5c4d7b2438d3 101 // Creates an event bound to the specified event queue
switches 0:5c4d7b2438d3 102 EventQueue queue;
switches 0:5c4d7b2438d3 103 Event<void()> event(&queue, doit);
switches 0:5c4d7b2438d3 104
switches 0:5c4d7b2438d3 105 // The event can be manually configured for special timing requirements
switches 0:5c4d7b2438d3 106 // specified in milliseconds
switches 0:5c4d7b2438d3 107 event.delay(10);
switches 0:5c4d7b2438d3 108 event.period(10000);
switches 0:5c4d7b2438d3 109
switches 0:5c4d7b2438d3 110 // Posted events are dispatched in the context of the queue's
switches 0:5c4d7b2438d3 111 // dispatch function
switches 0:5c4d7b2438d3 112 queue.dispatch();
switches 0:5c4d7b2438d3 113
switches 0:5c4d7b2438d3 114 // Events can also pass arguments to the underlying callback when both
switches 0:5c4d7b2438d3 115 // initially constructed and posted.
switches 0:5c4d7b2438d3 116 Event<void(int, int)> event(&queue, printf, "recieved %d and %d\n");
switches 0:5c4d7b2438d3 117
switches 0:5c4d7b2438d3 118 // Events can be posted multiple times and enqueue gracefully until
switches 0:5c4d7b2438d3 119 // the dispatch function is called.
switches 0:5c4d7b2438d3 120 event.post(1, 2);
switches 0:5c4d7b2438d3 121 event.post(3, 4);
switches 0:5c4d7b2438d3 122 event.post(5, 6);
switches 0:5c4d7b2438d3 123
switches 0:5c4d7b2438d3 124 queue.dispatch();
switches 0:5c4d7b2438d3 125 ```
switches 0:5c4d7b2438d3 126
switches 0:5c4d7b2438d3 127 Event queues easily align with module boundaries, where internal state can
switches 0:5c4d7b2438d3 128 be implicitly synchronized through event dispatch. Multiple modules can
switches 0:5c4d7b2438d3 129 use independent event queues, but still be composed through the
switches 0:5c4d7b2438d3 130 `EventQueue::chain` function.
switches 0:5c4d7b2438d3 131
switches 0:5c4d7b2438d3 132 ``` cpp
switches 0:5c4d7b2438d3 133 // Create some event queues with pending events
switches 0:5c4d7b2438d3 134 EventQueue a;
switches 0:5c4d7b2438d3 135 a.call(printf, "hello from a!\n");
switches 0:5c4d7b2438d3 136
switches 0:5c4d7b2438d3 137 EventQueue b;
switches 0:5c4d7b2438d3 138 b.call(printf, "hello from b!\n");
switches 0:5c4d7b2438d3 139
switches 0:5c4d7b2438d3 140 EventQueue c;
switches 0:5c4d7b2438d3 141 c.call(printf, "hello from c!\n");
switches 0:5c4d7b2438d3 142
switches 0:5c4d7b2438d3 143 // Chain c and b onto a's event queue. Both c and b will be dispatched
switches 0:5c4d7b2438d3 144 // in the context of a's dispatch function.
switches 0:5c4d7b2438d3 145 c.chain(&a);
switches 0:5c4d7b2438d3 146 b.chain(&a);
switches 0:5c4d7b2438d3 147
switches 0:5c4d7b2438d3 148 // Dispatching a will in turn dispatch b and c, printing hello from
switches 0:5c4d7b2438d3 149 // all three queues
switches 0:5c4d7b2438d3 150 a.dispatch();
switches 0:5c4d7b2438d3 151 ```
switches 0:5c4d7b2438d3 152
switches 0:5c4d7b2438d3 153