102 lines
7.6 KiB
C
102 lines
7.6 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 "StatusCode"
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StatusCode update(){
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digitalWrite(ledPin,power->newValue.BOOL); // use a standard Arduino function to turn on/off ledPin based on the boolean variable power->newValue.BOOL (see below for more info)
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return(StatusCode::OK); // return OK status code. There are other possibilties we will explore in later examples.
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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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// 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" nd 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 thre 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 Characteristic values:
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//
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// HomeSpan stores the values for its Characteristics in a union structure that allows for different types. The current value of a Characteristic
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// is stored in a union named "value" whereas upon an update request, the requested value is stored in a union named "newValue." To access the data
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// underlying either "value" or "newValue" you need to select the element of the union that matches the type. This is arguably sloppy, but using
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// C++ templates did not seem to make the process any less cumbersome. The names of each element are based on those specified in HAP Table 6-5, and map
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// to the Arduino data types as follows:
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//
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// BOOL -> (boolean)
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// UINT8 -> (uint8_t)
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// UINT16 -> (uint16_t)
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// UINT32 -> (uint32_t)
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// UINT64 -> (uint64_t)
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// INT -> (int)
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// FLOAT -> (double)
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// STRING -> (const char *)
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//
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// In the above example we created pointer named "power" to point to our newly-created "On" Characteristic. Hence, to access the current value of that
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// Characteristic we use "power->value.BOOL" To access to new value requested by HomeKit for this update, we use "power->newValue.BOOL" as shown above.
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// In most cases, we can manage the update by just reading the newValue requested, regardless of the whatever the current value is, but access to the
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// current value is available if neeed.
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// How to determine the value type for any Characteristic:
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//
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// All HomeKit Characteristics that have been implemented in HomeSpan are defined in "Services.h" in the HomeSpan library. The top part of "Services.h" defines
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// all the implemented Services. The bottom part defines the collection of Characteristics needed for those Services. Within the definition of each
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// Characteristic you'll see the HAP ID number, as well as the data type, such as (boolean), (uint16_t), etc. Select the corresponding element name
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// from the table above to access the underlying "value" or "newValue" data elements.
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// What the return code means:
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//
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// HomeKit requires each Characteristic to return a status code when an attempt to update it's value is made. HomeSpan automatically takes care of
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// some of 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 will apply the return code you specify to each of the Characteristics that were to be updated in that Service.
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// By returning StatusCode:OK 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 an OK status, 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 letting it know that the new values it requested have been sucessfully processed. At no point does
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// HomeKit as for, or allow, a value to be sent back from HomeSpan indicating the data in a Characteristic. When requesting an update, HomeKit simply
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// expects an okay or not okay.
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//
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// If for some reason the update() code cannot process an update request, it must return a HAP error code. These are listing in Settings.h. As noted above,
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// some are created automatically by HomeSpan and update() is never called. Others can only be determined from within an update() call and should be
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// used as the return value. The StatusCodes that can be used in this fashion are: OK, Unable, Busy. Any of the other StatusCode listed in Settings.h
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// are automatically handled by HomeSpan and should not be used as a return code, though nothing bad happens if you do. This is because the
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// HomeKit application itself only seems to distinguish an "OK" status code from a an not-"OK" code. HomeKit does not seem to process any error code
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// differently from any other error code. All error codes lead HomeKit to simply say "Device Not Reponding" in the Controller. This suggests that the
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// differences between "Unable" and "Busy" don't mean anything to HomeKit. They are all interpreted as an error, so pick anyone you'd like in the event
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// you can't update a characteristic to the requested value. Note that when you do return an error code, HomeSpan will NOT copy the newValue data elements
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// requested into the the current value data elements, thus keeping all Characteristics in the Service unchanged.
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//
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// Final note: There are very few reasons you should need to return an error code 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 element that are in-range.
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