1 page.title=Accessory Development Kit 2012 Guide
7 <h2>In this document</h2>
9 <li><a href="#components">Components</a></li>
10 <li><a href="#clock">Using the Alarm Clock</a></li>
11 <li><a href="#play-audio">Playing Audio</a></li>
12 <li><a href="#dev">Developing Accessories with ADK 2012</a>
14 <li><a href="#src-download">Downloading the ADK Source</a></li>
15 <li><a href="#dev-setup">Setting Up the Development Environment</a></li>
16 <li><a href="#alt-build">Using the ADK Alternative Build System</a></li>
19 <li><a href="#adk-conn">How the ADK Connects with Android Devices</a>
21 <li><a href="#adk-conn-bt">ADK Connection over Bluetooth</a></li>
22 <li><a href="#adk-conn-usb">ADK Connection over USB</a></li>
25 <li><a href="#audio-dock">USB Audio Dock Implementation</a></li>
30 <li><a href="https://developers.google.com/events/io/sessions/gooio2012/128/">
31 Google I/O Session Video</a></li>
32 <li><a href="http://source.android.com/tech/accessories/aoap/aoa.html">
33 Android Open Accessory Protocol</a></li>
34 <li><a href="http://source.android.com/tech/accessories/aoap/aoa2.html">
35 Android Open Accessory Protocol 2.0</a></li>
36 <li><a href="{@docRoot}guide/topics/connectivity/usb/accessory.html">
37 USB Accessory Dev Guide</a></li>
42 <p>The Android Accessory Development Kit (ADK) for 2012 is the latest reference implementation of an
43 <a href="http://source.android.com/tech/accessories/index.html">Android Open Accessory</a> device,
44 designed to help Android hardware accessory builders and software developers create accessories
45 for Android. The ADK 2012 is based on the <a href="http://arduino.cc">Arduino</a> open source
46 electronics prototyping platform, with some hardware and software extensions that allow it to
47 communicate with Android devices.</p>
49 <p>A limited number of these kits were produced and distributed at the Google I/O 2012 developer
50 conference. If you did not receive one of these kits, fear not! The specifications and design files
51 for the hardware were also released for use by manufacturers and hobbyists. You should expect to see
52 kits with similar features available for purchase, or you can build one yourself!</p>
54 <p>One of the important new features demonstrated by this ADK is the ability to play audio over a
55 USB connection. Be sure to check out the <a href="#audio-dock">reference implementation</a> of a USB
56 audio dock in this ADK if you are interested in making audio-related USB accessories for
59 <h2 id="components">Components</h2>
61 <p>The ADK 2012 is based on the Arduino open source electronics prototyping platform and is an open
62 hardware design. The hardware design files and firmware source code are included with the ADK
63 software download. The ADK contains two main physical hardware components:</p>
66 <li>Main processing board containing the microprocessor, USB connections, power connector and
67 input/output pins. This board can be removed and used separately from the rest of the hardware.</li>
68 <li>Shield containing sensors, LEDs, input controls, audio amplifier and speaker output, contained
69 in a custom, polygon box enclosure.</li>
72 <p>The main hardware features of the ADK are as follows:</p>
75 <li>An ARM 32-bit Cortex M3 micro-processor</li>
76 <li>Separate USB connections for an Android device and computer connection for programming and
78 <li>Sensors for light, color, proximity, temperature, humidity, barometric pressure, and
80 <li>Micro SD Card slot</li>
81 <li>Bluetooth support</li>
84 <p>The ADK comes preloaded with an alarm clock firmware program that you can use immediately. A
85 companion Android application, <a
86 href="https://play.google.com/store/apps/details?id=com.google.android.apps.adk2">ADK 2012</a>, is
87 available on Google Play. The source code for both the Android application and the ADK firmware (an
88 Arduino sketch) can be downloaded from this page.</p>
90 <p>The ADK 2012 also comes with additional parts to help you develop accessories with it,
94 <li>AC power adapter</li>
95 <li>USB A to Micro USB B connector cable</li>
96 <li>Micro USB B to Micro USB AB connector (small, rectangular plug)</li>
97 <li>Micro SD Card, preinstalled in the ADK SD Card socket</li>
100 <h2 id="clock">Using the Alarm Clock</h2>
102 <p>An alarm clock program comes preloaded on the ADK. This firmware program allows you to use the
103 ADK as an alarm clock.</p>
105 <p>To use the ADK as an alarm clock:</p>
108 <li>Open up the ADK by gently squeezing the two widest faces of the enclosure.</li>
109 <li>Attach the provided AC power adapter (round connector) to the main ADK board, or attach a USB
110 cable to the port marked <strong>Computer</strong> and a USB port on your computer.</li>
111 <li>Place and hold your fingertip over the clock symbol on the control face.
112 <p class="note"><strong>Note:</strong> You may need to hold your finger in place for 1-2
115 <li>Use the plus (+) and minus (-) symbols inside the clock digits to set the correct time.</li>
116 <li>Place your fingertip over the alarm clock symbol to activate alarm setting.</li>
117 <li>Use the plus (+) and minus (-) symbols inside the clock digits to set the alarm time.</li>
118 <li>Use the plus (+) and minus (-) symbols inside the last two clock digits to turn the alarm on
119 ({@code on}) or off ({@code oF}).</li>
120 <li>To set the alarm tone, place and hold your fingertip over the alarm clock symbol, then tap the
121 slider control on top of the enclosure.</li>
124 <p>To use the <strong>ADK 2012</strong> companion application for the alarm clock:</p>
127 <li>Load the companion application on your Android device running Android 3.1 (API Level 12) or
130 <li>Using an NFC-enabled Android device, unlock and hold the device against the left side of
131 the ADK enclosure. Follow the prompts to install the app.
133 <li>Start Google Play on your device, search for the <strong>ADK 2012</strong> application and
134 install it. If you cannot find the app, your device is not compatible. Try installing on another
138 <li>Connect your Android device to the ADK using one of the following methods:
140 <li id="conn-bt">To connect using Bluetooth:
142 <li>Plug the AC power adapter into the ADK.</li>
143 <li>On your Android device, turn Bluetooth On (<strong>Settings >
144 Bluetooth</strong>).</li>
145 <li>In the <strong>Settings</strong> page, press the <strong>Bluetooth</strong> option to
146 view paired devices.</li>
147 <li>Select <strong>Search for Devices</strong> to locate the ADK 2012 accessory and follow
148 the on screen instructions to connect.</li>
149 <li>After pairing is complete, start the <strong>ADK 2012</strong> app on your Android
151 <li>On the start screen, select the <strong>Use Bluetooth</strong> button.</li>
152 <li>In the list of paired devices, select the <strong>ADK 2012</strong> device.</li>
153 <li>The <strong>ADK 2012</strong> app should switch to the menu screen and you can start
154 interacting with the ADK accessory.</li>
158 <li id="conn-usb">To connect using USB:
160 <li>Plug the AC power adapter into the ADK.</li>
161 <li>Connect the Micro USB AB connector (small, rectangular plug) to the port labeled
162 <strong>Phone</strong> on the ADK board.</li>
163 <li>Unlock your Android device and connect the Micro USB B connector to your device.
164 <p class="note"><strong>Note:</strong> Your device must support Android USB accessory
165 mode. Devices that support this mode include Google Nexus devices.</p>
167 <li>On the Android device, you should see a prompt to connect to the <strong>ADK DemoKit
168 2012</strong>, select <strong>OK</strong>.</li>
169 <li>The <strong>ADK 2012</strong> app should start automatically and you can start
170 interacting with the ADK.</li>
177 <p class="note"><strong>Note:</strong> When using the ADK with a USB connection to an Android
178 device, make sure the AC power adapter is plugged in. A USB connection to a computer does not
179 provide sufficient voltage to power both the ADK and a USB connection to a device.</p>
182 <h2 id="play-audio">Playing Audio</h2>
184 <p>The ADK 2012 comes with audio output capabilities, including an amplifier and speaker. You can
185 use it to play audio from your Android device using either a Bluetooth or USB connection.</p>
187 <p>To play audio over Bluetooth:</p>
190 <li>Follow the instructions in the <a href="#conn-bt">previous section</a> to connect your Android
191 device to the ADK over Bluetooth.</li>
192 <li>On your Android device, navigate to the <strong>Settings > Bluetooth</strong> page to view the
193 list of paired devices, and make sure the ADK is connected.</li>
194 <li>Select the settings icon next to the <strong>ADK 2012</strong> item.</li>
195 <li>Make sure the <strong>Media Audio</strong> option is enabled.</li>
196 <li>Navigate to an application that plays music or other audio.</li>
197 <li>Play a song or sound and listen to it on the ADK speaker!</li>
200 <p>To play audio over USB, you must use a device running Android 4.1 (API Level 16) or higher:</p>
203 <li>Plug the AC power adapter into the ADK.</li>
204 <li>Connect the Micro USB AB connector (small, rectangular plug) to the Phone port on the ADK
206 <li>Unlock your Android device and connect the Micro USB B connector to your device.
207 <p class="note"><strong>Note:</strong> Your device must support Android USB accessory
208 mode. Devices that support this mode include Google Nexus devices.</p>
210 <li>On the Android device, you should see a prompt to connect to the <strong>ADK DemoKit
211 2012</strong>, select <strong>Cancel</strong> and allow the ADK to connect as a media device
213 <li>Navigate to an application that plays music or other audio.</li>
214 <li>Play a song or sound and listen to it on the ADK speaker!</li>
217 <p class="note"><strong>Note:</strong> When using the ADK with a USB connection to an Android
218 device, make sure the AC power adapter is plugged in. A USB connection to a computer does not
219 provide sufficient voltage to power both the ADK and a USB connection to a device.</p>
222 <h2 id="dev">Developing Accessories with ADK 2012</h2>
224 <p>The ADK 2012 is a hardware platform and a set of software libraries for prototyping Android
225 accessories. This section discusses how to set up a development environment for programming the ADK
226 to make it do what you want and to test software for building your own Android accessories.</p>
228 <h3 id="src-download">Downloading the ADK Source</h3>
230 <p>The support software and hardware specifications for the ADK 2012 are available from the Android
231 source repository. Follow the instructions below to obtain the source material for the ADK.</p>
233 <p>To download the ADK 2012 software, source code and hardware design specifications.</p>
236 <li>Download and install <a href="http://git-scm.com/download">Git</a> for your development
238 <li>Download and setup the {@code repo} tool, as described on the <a
239 href="http://source.android.com/source/downloading.html#installing-repo">Android open source
241 <p class="note"><strong>Note:</strong> Developers using Windows must use a Linux compatibility
242 package, such as <a href="http://www.cygwin.com/">cygwin</a>, to install and run {@code repo}.
243 Within your compatibility environment, you must install {@code curl}, {@code git} and {@code
244 python} to be able to download and use the {@code repo} tool.</p>
246 <li>In a terminal window, create a new directory for the downloaded source files, initialize and
247 synchronize a local repository:
249 $> mkdir android-accessories
250 $> cd android-accessories
251 $> repo init -u https://android.googlesource.com/accessories/manifest
257 <p>After successfully completing this process, you should have the source code and tools for
258 working with the ADK 2012:</p>
261 <li>{@code adk2012/board} - Source code and hardware design files for the ADK 2012</li>
262 <li>{@code adk2012/app} - Source code for the ADK 2012 Android companion application</li>
263 <li>{@code external/ide} - Source code for the ADK 2012 Integrated Development Environment
265 <li>{@code external/toolchain} - The toolchain used by the ADK 2012 IDE</li>
269 <h3 id="dev-setup">Setting Up the Development Environment</h3>
271 <p>The ADK 2012 comes with an integrated development environment (IDE) that you use to develop
272 software and program the ADK 2012 accessory. The following instructions explain how to setup and run
273 the ADK 2012 IDE.</p>
275 <p>To set up and run the ADK 2012 IDE:</p>
278 <li>Download and install the Java Development Kit 6 or higher from <a
279 href="http://java.oracle.com">java.oracle.com</a>.</li>
280 <li>Download the ADK 2012 IDE for your development platform:
282 <li><a href="https://dl-ssl.google.com/android/adk/adk2012_ide-win32-20120629.zip">
284 <li><a href="https://dl-ssl.google.com/android/adk/adk2012_ide-macosx-20120626.zip">
287 <a href="https://dl-ssl.google.com/android/adk/adk2012_ide-linux32-20120626.tgz">32bit</a>,
288 <a href="https://dl-ssl.google.com/android/adk/adk2012_ide-linux64-20120626.tgz">64bit</a>
292 <li>Unpack the downloaded archive.</li>
293 <li>Run the application by navigating to the unpacked {@code ADK2012_IDE/} folder and execute
294 the {@code arduino} file.</li>
297 <p>After you have successfully installed and run the ADK 2012 IDE, you must configure it to use
298 the ADK 2012 library.</p>
300 <p>To configure the ADK 2012 IDE for use with the ADK libraries:</p>
303 <li>Start the ADK 2012 IDE and choose <strong>File > Preferences</strong>.</li>
304 <li>In the <strong>Preferences</strong> dialog, make a note of the <strong>Sketchbook
305 location</strong> directory.</li>
306 <li>Copy the {@code <adk-source-download>/adk2012/board/library/ADK2} directory and its
307 contents into your {@code sketchbook/libraries/} directory, so that you create a {@code
308 sketchbook/libraries/ADK2} directory.</li>
309 <li>Stop and restart the <strong>ADK 2012 IDE</strong>.</li>
310 <li>In the IDE, choose <strong>File > Examples > ADK2</strong> and then choose one of the example
313 <li><strong>clock</strong> - The sketch that is preloaded onto the ADK 2012.</li>
314 <li><strong>BluetoothScan</strong> - An example sketch demonstrating code that connects an
315 accessory to an Android device over Bluetooth.</li>
316 <li><strong>usbaccessory</strong> - An example sketch demonstrating code that connects an
317 accessory to an Android device through a USB cable.</li>
320 <li>Connect a Micro USB cable from the <strong>Computer</strong> port on the ADK board to your
321 development computer.</li>
322 <li>In the <strong>ADK 2012 IDE</strong>, establish a serial port connection with the ADK by
323 selecting <strong>Tools > Serial Port</strong> and selecting the serial port for the ADK.</li>
324 <li>In the <strong>ADK 2012 IDE</strong>, choose the ADK by selecting<strong>Tools > Board >
325 Google ADK2</strong>.</li>
326 <li>Modify an example sketch or create your own.</li>
327 <li>Upload the sketch to the ADK by choosing <strong>File > Upload</strong>. When the <strong>ADK
328 2012 IDE</strong> reports <strong>Done uploading</strong>, the sketch is uploaded and the ADK is
329 ready to communicate with your Android device.</li>
332 <h3 id="alt-build">Using the ADK Alternative Build System</h3>
334 <p>An alternative, make file-based build and upload system is also available for the ADK 2012. This
335 system is command line based and intended for production environments where using an IDE environment
336 to load software onto accessory hardware may be inconvenient or undesirable.</p>
338 <p>To setup the environment:</p>
340 <li><a href="#src-download">Download</a> the ADK 2012 source code files.</li>
341 <li>In a terminal window, navigate to {@code
342 <adk-source-download>/adk2012/board/MakefileBasedBuild}.</li>
343 <li>Execute the following command and follow the instructions:
344 <pre>$> ./setup</pre>
348 <p>To build a program for your accessory:</p>
350 <li>Place your accessory code in the {@code MakefileBasedBuild/app} directory, including all
351 required library files. See the {@code app/main.c} file for an example of the program format.</li>
352 <li>Execute the following command and follow the instructions:
353 <pre>$> ./build</pre>
357 <p>To load the program on your accessory hardware:</p>
359 <li>Run the build process above and make sure your program compiled successfully.</li>
360 <li>Attach the accessory via USB cable to your development computer.</li>
361 <li>Check which port the accessory is attached to and modify the {@code UART} variable in the
362 {@code flash} script to the correct port address. On linux machines, the port address is typically
363 {@code /dev/ttyUSB0}.</li>
364 <li>Execute the following command to load the program on the accessory:
365 <pre>$> ./flash</pre></li>
368 <h2 id="adk-conn">How the ADK Connects with Android Devices</h2>
370 <p>The essential feature of any Android accessory is its ability to connect and communicate with an
371 Android device. Creating a fast and reliable connection between your accessory and Android devices
372 is the first order of business when building software for an accessory. This section describes the
373 connection and communication essentials used in the ADK 2012 so that you can apply them to
374 developing your own Android accessories.</p>
376 <h3 id="adk-conn-bt">ADK Connection over Bluetooth</h3>
378 <p>The ADK 2012 app and hardware accessory use a Bluetooth Serial Port Profile (SPP) connection to
379 communicate. This connection allows two way communication between the ADK accessory and Android
382 <p class="note"><strong>Note:</strong> The implementation of the ADK hardware allows the use of
383 other profiles and multiple connections. However, the basic communication between the ADK 2012
384 accessory and the Android application uses SPP.</p>
386 <h4 id="acc-bt-code">Accessory Bluetooth Code</h4>
388 <p>In order to enable Bluetooth communications, the {@code clock.ino} sketch for the ADK 2012
389 accessory calls a {@code btStart()} method during the {@code setup()} method to enable radio
390 frequency communications and start listening for Bluetooth connections:</p>
403 L.btEnable(adkBtConnectionRequest, adkBtLinkKeyRequest, adkBtLinkKeyCreated,
404 adkBtPinRequest, NULL);
406 dlci = L.btRfcommReserveDlci(RFCOMM_DLCI_NEED_EVEN);
408 if(!dlci) dbgPrintf("BTADK: failed to allocate DLCI\n");
411 //change descriptor to be valid...
412 for(i = 0, f = -1; i < sizeof(sdpDescrADK); i++){
414 if(sdpDescrADK[i] == MAGIX){
420 if(i != sizeof(sdpDescrADK) || f == -1){
422 dbgPrintf("BTADK: failed to find a single marker in descriptor\n");
423 L.btRfcommReleaseDlci(dlci);
427 sdpDescrADK[f] = dlci >> 1;
429 dbgPrintf("BTADK has DLCI %u\n", dlci);
431 L.btRfcommRegisterPort(dlci, btAdkPortOpen, btAdkPortClose, btAdkPortRx);
432 L.btSdpServiceDescriptorAdd(sdpDescrADK, sizeof(sdpDescrADK));
437 <p>Notice that the {@code sdpDescrADK} object contains a Universally Unique Identifier (UUID) in the
438 variable {@code BT_ADK_UUID}. This identifier <em>must match</em> the device UUID provided in the
439 {@link android.bluetooth.BluetoothSocket} connection request in the Android application code.</p>
441 <p>Once Bluetooth is enabled with the code shown above, the accessory listens for connection
442 requests. The ADK library handles listening and connection details, so the accessory calls
443 {@code ADK::adkEventProcess()} once during each loop execution:</p>
449 L.adkEventProcess(); //let the adk framework do its thing
454 <p>If a Bluetooth connection has been established, any commands are routed to the
455 {@code btAdkPortRx()} callback method (which was registered with the ADK library as part of the
456 {@code btStart()} method) and processed accordingly. The ADK accessory sends messages back through
457 the Bluetooth connection using the {@code ADK::btRfcommPortTx()} method.
458 For more details, review the implementations of these methods in the {@code clock.ino} sketch.</p>
460 <h4 id="app-bt-code">Android App Bluetooth Code</h4>
462 <p>In the ADK 2012 Android app, the code for handling Bluetooth connections is encapsulated in in a
463 {@code BTConnection} class. In this class, the application requests access to the Bluetooth adapter
464 and negotiates a connection with the ADK 2012 accessory. Here is a summary of the relevant code:</p>
467 mAdapter = BluetoothAdapter.getDefaultAdapter();
468 BluetoothDevice device = mAdapter.getRemoteDevice(address);
469 mSocket = device.createInsecureRfcommSocketToServiceRecord(ADK_UUID);
473 <p>Note the {@code ADK_UUID} parameter in the second line. This identifier must match the identifier
474 output by the accessory (the {@code BT_ADK_UUID} variable mentioned earlier), otherwise the protocol
475 negotiation fails and the {@link android.bluetooth.BluetoothSocket} is not created. Once a
476 connection is established, you obtain {@link java.io.InputStream} and {@link java.io.OutputStream}
477 objects from the socket to communicate with the accessory:</p>
480 mInStream = mSocket.getInputStream();
481 mOutStream = mSocket.getOutputStream();
484 <p>Review the {@code BTConnection.java} file provided in the ADK 2012 software download for more
485 implementation details.</p>
487 <h3 id="adk-conn-usb">ADK Connection over USB</h3>
489 <p>The ADK 2012 app and hardware accessory can also use a USB connection to communicate, similar to
490 the original ADK.</p>
492 <h4 id="acc-usb-code">Accessory USB Code</h4>
494 <p>The ADK library takes care of most of the implementation details for a USB connection, the
495 accessory code must make a few calls to initialize USB connectivity, including setting the accessory
496 identification strings:</p>
502 L.usbSetAccessoryStringVendor(...);
503 L.usbSetAccessoryStringName(...);
504 L.usbSetAccessoryStringLongname(...);
505 L.usbSetAccessoryStringVersion(...);
506 L.usbSetAccessoryStringUrl(...);
507 L.usbSetAccessoryStringSerial(...);
513 <p class="note"><strong>Note:</strong> The identification strings must match the USB accessory
514 filter settings specified in the connecting Android application,otherwise the application cannot
515 connect with the accessory.</p>
517 <p>Once USB is enabled with code shown above, the accessory listens for connection requests. The ADK
518 library handles listening and connection details, so the accessory calls {@code
519 ADK::adkEventProcess()} once during each loop execution:</p>
525 L.adkEventProcess(); //let the adk framework do its thing
530 <p>The accessory must then check for a live USB connection to process commands and send
531 messages. Here is a summary of the relevant code:</p>
535 if (L.accessoryConnected()) {
536 int recvLen = L.accessoryReceive(msg, sizeof(msg));
538 ... // process message
541 L.accessorySend(outmsg, outmsgLen);
547 <p>For more details, review the implementations of these methods in the {@code clock.ino}
550 <h4 id="app-usb-code">Android App USB Code</h4>
552 <p>In the ADK 2012 Android app, the code for handling USB connections is encapsulated in a
553 {@code UsbConnection} class. This class sets up a {@link android.content.BroadcastReceiver} to
554 listen for USB events and then attempts to connect when a matching connection event is received.
555 Here is a summary of the relevant code:</p>
558 import com.android.future.usb.UsbAccessory;
559 import com.android.future.usb.UsbManager;
561 mUSBManager = UsbManager.getInstance(this);
562 UsbAccessory acc = mUSBManager.getAccessoryList()[0];
564 if (!mUSBManager.hasPermission(acc)) return;
567 <p>The ADK 2012 app uses the support library to implement the USB accessory connections, in order to
568 support devices running Android 2.3.4 (API Level 10). If you only need to support Android
569 3.1 (API Level 12) and higher devices, you can replace the first 4 lines the following code:</p>
572 import android.hardware.usb.UsbAccessory
573 import android.hardware.usb.UsbManager
575 mUSBManager = (UsbManager) getSystemService(Context.USB_SERVICE);
576 UsbAccessory acc = (UsbAccessory)
577 intent.getParcelableExtra(UsbManager.EXTRA_ACCESSORY);
580 <p>Note that the app only receives events when the USB accessory identification information matches
581 the information in the {@code res/xml/usb_accessory_filter.xml} file, referenced by the
582 application’s manifest statement:</p>
586 android:name="android.hardware.usb.action.USB_ACCESSORY_ATTACHED"
587 android:resource="@xml/usb_accessory_filter" />
590 <p>Connections from other USB devices are not received by the ADK 2012 accessory.</p>
592 <p>Once the connection is established, the app can communicate with the accessory through file input
593 and output streams, as shown in the following example code:</p>
596 ParcelFileDescriptor mFD = mUSBManager.openAccessory(acc);
598 FileDescripter fd = mFD.getFileDescriptor();
599 mIS = new FileInputStream(fd); // use this to receive messages
600 mOS = new FileOutputStream(fd); // use this to send commands
604 <p>Review the {@code UsbConnection.java} file provided in the ADK 2012 source code for more
605 implementation details.</p>
607 <h2 id="audio-dock">USB Audio Dock Implementation</h2>
609 <p>One of the important new features introduced with the ADK 2012 is the ability to play audio over
610 a USB connection. This innovation was introduced as an update to Android Open Accessory (AOA)
611 <a href="http://source.android.com/tech/accessories/aoap/aoa2.html">protocol 2.0</a> and is
612 available on devices running Android 4.1 (API Level 16) and higher.</p>
614 <p>The ADK 2012 provides a reference implementation of this functionality for accessory developers.
615 No software application is required to be installed on the connected Android device, accessory
616 developers only need to support AOA v2. This implementation demonstrates audio output of 16bit,
617 44.1kHz stereo PCM source data compressed into a single channel due to the audio hardware available
618 on the accessory.</p>
620 <p>Using the audio output features provided by the ADK library requires only a few function calls.
621 The first few calls are in the accessory {@code setup()} routine, which prepare the accessory for
622 USB connections and audio output, as summarized in the code example below:</p>
633 <p>For more information about the {@code ADK::audioInit()} function, see the {@code
634 libraries/ADK/Audio.c} library file. For more information about the {@code ADK::usbh_init()}
635 function, see the {@code libraries/ADK/Usbh.c} library file.</p>
637 <p>After completing this setup, the {@code loop()} function calls {@code ADK::adkEventProcess()} to
638 handle audio output and other ADK functions:</p>
644 L.adkEventProcess(); //let the adk framework do its thing
649 <p>This call executes task queuing for the ADK and as part of the execution process, the task queue
650 executes {@code usbh_work()} in {@code libraries/ADK/Usbh.c}, which handles audio output requests.
651 Review the implementation of this function for details. For additional implementation details on
652 audio output, see the {@code libraries/ADK/accessory.c} library file.</p>