ON Semiconductor / mbed-os

5.2.1 - Updated I2C files

Dependents:   mbed-TFT-example-NCS36510 mbed-Accelerometer-example-NCS36510 mbed-Accelerometer-example-NCS36510

events/README.md@1:f30bdcd2b33b, 2017-02-27 (annotated)

Committer:
jacobjohnson
Date:
Mon Feb 27 17:45:05 2017 +0000
Revision:
1:f30bdcd2b33b
Parent:
0:098463de4c5d 
changed the inputscale from 1 to 7 in analogin_api.c.  This will need to be changed later, and accessed from the main level, but for now this allows the  adc to read a value from 0 to 3.7V, instead of just up to 1V.;

Who changed what in which revision?

UserRevisionLine numberNew contents of line
group-onsemi 0:098463de4c5d 1 ## The mbed-events library ##
group-onsemi 0:098463de4c5d 2
group-onsemi 0:098463de4c5d 3 The mbed-events library provides a flexible queue for scheduling events.
group-onsemi 0:098463de4c5d 4
group-onsemi 0:098463de4c5d 5 ``` cpp
group-onsemi 0:098463de4c5d 6 #include "mbed_events.h"
group-onsemi 0:098463de4c5d 7 #include <stdio.h>
group-onsemi 0:098463de4c5d 8
group-onsemi 0:098463de4c5d 9 int main() {
group-onsemi 0:098463de4c5d 10 // creates a queue with the default size
group-onsemi 0:098463de4c5d 11 EventQueue queue;
group-onsemi 0:098463de4c5d 12
group-onsemi 0:098463de4c5d 13 // events are simple callbacks
group-onsemi 0:098463de4c5d 14 queue.call(printf, "called immediately\n");
group-onsemi 0:098463de4c5d 15 queue.call_in(2000, printf, "called in 2 seconds\n");
group-onsemi 0:098463de4c5d 16 queue.call_every(1000, printf, "called every 1 seconds\n");
group-onsemi 0:098463de4c5d 17
group-onsemi 0:098463de4c5d 18 // events are executed by the dispatch method
group-onsemi 0:098463de4c5d 19 queue.dispatch();
group-onsemi 0:098463de4c5d 20 }
group-onsemi 0:098463de4c5d 21 ```
group-onsemi 0:098463de4c5d 22
group-onsemi 0:098463de4c5d 23 The mbed-events library can be used as a normal event loop, or it can be
group-onsemi 0:098463de4c5d 24 backgrounded on a single hardware timer or even another event loop. It is
group-onsemi 0:098463de4c5d 25 both thread and irq safe, and provides functions for easily composing
group-onsemi 0:098463de4c5d 26 independent event queues.
group-onsemi 0:098463de4c5d 27
group-onsemi 0:098463de4c5d 28 The mbed-events library can act as a drop-in scheduler, provide synchronization
group-onsemi 0:098463de4c5d 29 between multiple threads, or just act as a mechanism for moving events out of
group-onsemi 0:098463de4c5d 30 interrupt contexts.
group-onsemi 0:098463de4c5d 31
group-onsemi 0:098463de4c5d 32 ### Usage ###
group-onsemi 0:098463de4c5d 33
group-onsemi 0:098463de4c5d 34 The core of the mbed-events library is the [EventQueue](EventQueue.h) class,
group-onsemi 0:098463de4c5d 35 which represents a single event queue. The `EventQueue::dispatch` function
group-onsemi 0:098463de4c5d 36 runs the queue, providing the context for executing events.
group-onsemi 0:098463de4c5d 37
group-onsemi 0:098463de4c5d 38 ``` cpp
group-onsemi 0:098463de4c5d 39 // Creates an event queue enough buffer space for 32 Callbacks. This
group-onsemi 0:098463de4c5d 40 // is the default if no argument was provided. Alternatively the size
group-onsemi 0:098463de4c5d 41 // can just be specified in bytes.
group-onsemi 0:098463de4c5d 42 EventQueue queue(32*EVENTS_EVENT_SIZE);
group-onsemi 0:098463de4c5d 43
group-onsemi 0:098463de4c5d 44 // Events can be posted to the underlying event queue with dynamic
group-onsemi 0:098463de4c5d 45 // context allocated from the specified buffer
group-onsemi 0:098463de4c5d 46 queue.call(printf, "hello %d %d %d %d\n", 1, 2, 3, 4);
group-onsemi 0:098463de4c5d 47 queue.call(&serial, &Serial::printf, "hi\n");
group-onsemi 0:098463de4c5d 48
group-onsemi 0:098463de4c5d 49 // The dispatch function provides the context for the running the queue
group-onsemi 0:098463de4c5d 50 // and can take a millisecond timeout to run for a fixed time or to just
group-onsemi 0:098463de4c5d 51 // dispatch any pending events
group-onsemi 0:098463de4c5d 52 queue.dispatch();
group-onsemi 0:098463de4c5d 53 ```
group-onsemi 0:098463de4c5d 54
group-onsemi 0:098463de4c5d 55 The EventQueue class provides several call functions for posting events
group-onsemi 0:098463de4c5d 56 to the underlying event queue. The call functions are thread and irq safe,
group-onsemi 0:098463de4c5d 57 don't need the underlying loop to be running, and provide an easy mechanism
group-onsemi 0:098463de4c5d 58 for moving events out of interrupt contexts.
group-onsemi 0:098463de4c5d 59
group-onsemi 0:098463de4c5d 60 ``` cpp
group-onsemi 0:098463de4c5d 61 // Simple call function registers events to be called as soon as possible
group-onsemi 0:098463de4c5d 62 queue.call(doit);
group-onsemi 0:098463de4c5d 63 queue.call(printf, "called immediately\n");
group-onsemi 0:098463de4c5d 64
group-onsemi 0:098463de4c5d 65 // The call_in function registers events to be called after a delay
group-onsemi 0:098463de4c5d 66 // specified in milliseconds
group-onsemi 0:098463de4c5d 67 queue.call_in(2000, doit_in_two_seconds);
group-onsemi 0:098463de4c5d 68 queue.call_in(300, printf, "called in 0.3 seconds\n");
group-onsemi 0:098463de4c5d 69
group-onsemi 0:098463de4c5d 70 // The call_every function registers events to be called repeatedly
group-onsemi 0:098463de4c5d 71 // with a period specified in milliseconds
group-onsemi 0:098463de4c5d 72 queue.call_every(2000, doit_every_two_seconds);
group-onsemi 0:098463de4c5d 73 queue.call_every(400, printf, "called every 0.4 seconds\n");
group-onsemi 0:098463de4c5d 74 ```
group-onsemi 0:098463de4c5d 75
group-onsemi 0:098463de4c5d 76 The call functions return an id that uniquely represents the event in the
group-onsemi 0:098463de4c5d 77 the event queue. This id can be passed to `EventQueue::cancel` to cancel
group-onsemi 0:098463de4c5d 78 an in-flight event.
group-onsemi 0:098463de4c5d 79
group-onsemi 0:098463de4c5d 80 ``` cpp
group-onsemi 0:098463de4c5d 81 // The event id uniquely represents the event in the queue
group-onsemi 0:098463de4c5d 82 int id = queue.call_in(100, printf, "will this work?\n");
group-onsemi 0:098463de4c5d 83
group-onsemi 0:098463de4c5d 84 // If there was not enough memory necessary to allocate the event,
group-onsemi 0:098463de4c5d 85 // an id of 0 is returned from the call functions
group-onsemi 0:098463de4c5d 86 if (id) {
group-onsemi 0:098463de4c5d 87 error("oh no!");
group-onsemi 0:098463de4c5d 88 }
group-onsemi 0:098463de4c5d 89
group-onsemi 0:098463de4c5d 90 // Events can be cancelled as long as they have not been dispatched. If the
group-onsemi 0:098463de4c5d 91 // event has already expired, cancel has no side-effects.
group-onsemi 0:098463de4c5d 92 queue.cancel(id);
group-onsemi 0:098463de4c5d 93 ```
group-onsemi 0:098463de4c5d 94
group-onsemi 0:098463de4c5d 95 For a more fine-grain control of event dispatch, the `Event` class can be
group-onsemi 0:098463de4c5d 96 manually instantiated and configured. An `Event` represents an event as
group-onsemi 0:098463de4c5d 97 a C++ style function object and can be directly passed to other APIs that
group-onsemi 0:098463de4c5d 98 expect a callback.
group-onsemi 0:098463de4c5d 99
group-onsemi 0:098463de4c5d 100 ``` cpp
group-onsemi 0:098463de4c5d 101 // Creates an event bound to the specified event queue
group-onsemi 0:098463de4c5d 102 EventQueue queue;
group-onsemi 0:098463de4c5d 103 Event<void()> event(&queue, doit);
group-onsemi 0:098463de4c5d 104
group-onsemi 0:098463de4c5d 105 // The event can be manually configured for special timing requirements
group-onsemi 0:098463de4c5d 106 // specified in milliseconds
group-onsemi 0:098463de4c5d 107 event.delay(10);
group-onsemi 0:098463de4c5d 108 event.period(10000);
group-onsemi 0:098463de4c5d 109
group-onsemi 0:098463de4c5d 110 // Posted events are dispatched in the context of the queue's
group-onsemi 0:098463de4c5d 111 // dispatch function
group-onsemi 0:098463de4c5d 112 queue.dispatch();
group-onsemi 0:098463de4c5d 113
group-onsemi 0:098463de4c5d 114 // Events can also pass arguments to the underlying callback when both
group-onsemi 0:098463de4c5d 115 // initially constructed and posted.
group-onsemi 0:098463de4c5d 116 Event<void(int, int)> event(&queue, printf, "recieved %d and %d\n");
group-onsemi 0:098463de4c5d 117
group-onsemi 0:098463de4c5d 118 // Events can be posted multiple times and enqueue gracefully until
group-onsemi 0:098463de4c5d 119 // the dispatch function is called.
group-onsemi 0:098463de4c5d 120 event.post(1, 2);
group-onsemi 0:098463de4c5d 121 event.post(3, 4);
group-onsemi 0:098463de4c5d 122 event.post(5, 6);
group-onsemi 0:098463de4c5d 123
group-onsemi 0:098463de4c5d 124 queue.dispatch();
group-onsemi 0:098463de4c5d 125 ```
group-onsemi 0:098463de4c5d 126
group-onsemi 0:098463de4c5d 127 Event queues easily align with module boundaries, where internal state can
group-onsemi 0:098463de4c5d 128 be implicitly synchronized through event dispatch. Multiple modules can
group-onsemi 0:098463de4c5d 129 use independent event queues, but still be composed through the
group-onsemi 0:098463de4c5d 130 `EventQueue::chain` function.
group-onsemi 0:098463de4c5d 131
group-onsemi 0:098463de4c5d 132 ``` cpp
group-onsemi 0:098463de4c5d 133 // Create some event queues with pending events
group-onsemi 0:098463de4c5d 134 EventQueue a;
group-onsemi 0:098463de4c5d 135 a.call(printf, "hello from a!\n");
group-onsemi 0:098463de4c5d 136
group-onsemi 0:098463de4c5d 137 EventQueue b;
group-onsemi 0:098463de4c5d 138 b.call(printf, "hello from b!\n");
group-onsemi 0:098463de4c5d 139
group-onsemi 0:098463de4c5d 140 EventQueue c;
group-onsemi 0:098463de4c5d 141 c.call(printf, "hello from c!\n");
group-onsemi 0:098463de4c5d 142
group-onsemi 0:098463de4c5d 143 // Chain c and b onto a's event queue. Both c and b will be dispatched
group-onsemi 0:098463de4c5d 144 // in the context of a's dispatch function.
group-onsemi 0:098463de4c5d 145 c.chain(&a);
group-onsemi 0:098463de4c5d 146 b.chain(&a);
group-onsemi 0:098463de4c5d 147
group-onsemi 0:098463de4c5d 148 // Dispatching a will in turn dispatch b and c, printing hello from
group-onsemi 0:098463de4c5d 149 // all three queues
group-onsemi 0:098463de4c5d 150 a.dispatch();
group-onsemi 0:098463de4c5d 151 ```
group-onsemi 0:098463de4c5d 152
group-onsemi 0:098463de4c5d 153