101 lines
8.3 KiB
C
101 lines
8.3 KiB
C
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////////////////////////////////////
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// DEVICE-SPECIFIC LED SERVICES //
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////////////////////////////////////
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// HERE'S WHERE WE DEFINE OUR NEW LED SERVICE!
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struct DEV_LED : Service::LightBulb { // First we create a derived class from the HomeSpan LightBulb Service
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int ledPin; // this variable stores the pin number defined for this LED
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SpanCharacteristic *power; // here we create a generic pointer to a SpanCharacteristic named "power" that we will use below
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// Next we define the constructor for DEV_LED. Note that it takes one argument, ledPin,
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// which specifies the pin to which the LED is attached.
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DEV_LED(int ledPin) : Service::LightBulb(){
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power=new Characteristic::On(); // this is where we create the On Characterstic we had previously defined in setup(). Save this in the pointer created above, for use below
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this->ledPin=ledPin; // don't forget to store ledPin...
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pinMode(ledPin,OUTPUT); // ...and set the mode for ledPin to be an OUTPUT (standard Arduino function)
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} // end constructor
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// Finally, we over-ride the default update() method with instructions that actually turn on/off the LED. Note update() returns type boolean
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boolean update(){
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digitalWrite(ledPin,power->getNewVal()); // use a standard Arduino function to turn on/off ledPin based on the return of a call to power->getNewVal() (see below for more info)
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return(true); // return true to indicate the update was successful (otherwise create code to return false if some reason you could not turn on the LED)
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} // update
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};
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//////////////////////////////////
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// HOW update() WORKS:
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// ------------------
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//
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// Whenever a HomeKit controller requests HomeSpan to update a Characteristic, HomeSpan calls the update() method for the SERVICE that contains the
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// Characteristic. It calls this only one time, even if multiple Characteristics updates are requested for that Service. For example, if you
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// direct HomeKit to turn on a light and set it to 50% brightness, it will send HomeSpan two requests: one to update the "On" Characteristic of the
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// LightBulb Service from "false" to "true" and another to update the "Brightness" Characteristic of that same Service to 50. This is VERY inefficient
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// and would require the user to process multiple updates to the same Service.
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//
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// Instead, HomeSpan combines both requests into a single call to update() for the Service itself, where you can process all of the Characteristics
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// that change at the same time. In the example above, we only have a single Characteristic to deal with, so this does not mean much. But in later
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// examples we'll see how this works with multiple Characteristics.
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// HOW TO ACCESS A CHARACTERISTIC'S NEW AND CURRENT VALUES
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// -------------------------------------------------------
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//
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// HomeSpan stores the values for its Characteristics in a union structure that allows for different types, such as floats, booleans, etc. The specific
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// types are defined by HAP for each Characteristic. Looking up whether a Characteristic is a uint8 or uint16 can be tiresome, so HomeSpan abstracts
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// all these details. Since C++ adheres to strict variable typing, this is done through the use of template methods. Every Characteristic supports
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// the following two methods:
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//
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// getVal<type>() - returns the CURRENT value of the Characterisic, after casting into "type"
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// getNewVal<type>() - returns the NEW value (i.e. to be updated) of the Characteritic, after casting into "type"
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//
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// For example, MyChar->getVal<int>() returns the current value of SpanCharacterstic MyChar as an int, REGARDLESS of how the value is stored by HomeSpan.
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// Similarly, MyChar->getVal<double>() returns a value as a double, even it is stored as as a boolean (in which case you'll either get 0.00 or 1.00).
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// Of course you need to make sure you understand the range of expected values so that you don't try to access a value stored as 2-byte int using getVal<uint8_t>().
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// But it's perfectly okay to use getVal<int>() to access the value of a Characteristic that HAP insists on storing as a float, even though its range is
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// strictly between 0 and 100 in steps of 1. Knowing the range and step size is all you need to know in determining you can access this as an <int> or even a <uint8_t>.
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//
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// Because most Characteristic values can properly be cast into int, getVal and getNewVal both default to <int> if the template parameter is not specified.
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// As you can see above, we retrieved the new value HomeKit requested for the On Characteristic that we named "power" by simply calling power->getNewVal().
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// Since no template parameter is specified, getNewVal() will return an int. And since the On Characteristic is natively stored as a boolean, getNewVal()
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// will either return a 0 or a 1, depending on whether HomeKit is requesting the Characteristic to be turned off or on.
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//
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// You may also note that in the above example we needed to use getNewVal(), but did not use getVal() anywhere. This is because we know exactly what
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// to do if HomeKit requests an LED to be turned on or off. The current status of the LED (on or off) does not matter. In latter examples we will see
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// instances where the current state of the device DOES matter, and we will need to access both current and new values.
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//
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// Finally, there is one additional method for Characteristics that is not used above but will be in later examples: updated(). This method returns a
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// boolean indicating whether HomeKit has requested a Characteristic to be updated, which means that getNewVal() will contain the new value it wants to set
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// for that Characteristic. For a Service with only one Characteristic, as above, we don't need to ask if "power" was updated using power->updated() because
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// the fact the the update() method for the Service is being called means that HomeKit is requesting an update, and the only thing to update is "power".
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// But for Services with two or more Characteristics, update() can be called with a request to update only a subset of the Characteristics. We will
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// find good use for the updated() method in later, multi-Characteristic examples.
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// UNDER THE HOOD: WHAT THE RETURN CODE FOR UPDATE() DOES
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// ------------------------------------------------------
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//
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// HomeKit requires each Characteristic to return a special HAP status code when an attempt to update its value is made. HomeSpan automatically takes care of
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// most of the errors, such as a Characteristic not being found, or a request to update a Characteristic that is read only. In these cases update() is never
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// even called. But if it is, HomeSpan needs to return a HAP status code for each of the Characteristics that were to be updated in that Service.
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// By returning "true" you tell HomeSpan that the newValues requested are okay and you've made the required updates to the physical device. Upon
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// receiving a true return value, HomeSpan updates the Characteristics themselves by copying the "newValue" data elements into the current "value" data elements.
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// HomeSpan then sends a message back to HomeKit with a HAP code representing "OK," which lets the Controller know that the new values it requested have been
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// sucessfully processed. At no point does HomeKit ask for, or allow, a data value to be sent back from HomeSpan indicating the data in a Characteristic.
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// When requesting an update, HomeKit simply expects a HAP status code of OK, or some other status code representing an error. To tell HomeSpan to send the Controller
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// an error code, indicating that you were not able to successfully process the update, simply have update() return a value of "false." HomeSpan converts a
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// return of "false" to the HAP status code representing "UNABLE," which will cause the Controller to show that the device is not responding.
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// There are very few reasons you should need to return "false" since so much checking is done in advance by either HomeSpan or HomeKit
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// itself. For instance, HomeKit does not allow you to use the Controller, or even Siri, to change the brightness of LightBulb to a value outside the
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// range of allowable values you specified. This means that any update() requests you receive should only contain newValue data elements that are in-range.
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//
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