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1page.title=Accessory Development Kit 2012 Guide
2@jd:body
3
4<div id="qv-wrapper">
5  <div id="qv">
6    <h2>In this document</h2>
7    <ol>
8      <li><a href="#components">Components</a></li>
9      <li><a href="#clock">Using the Alarm Clock</a></li>
10      <li><a href="#play-audio">Playing Audio</a></li>
11      <li><a href="#dev">Developing Accessories with ADK 2012</a>
12        <ol>
13          <li><a href="#src-download">Downloading the ADK Source</a></li>
14          <li><a href="#dev-setup">Setting Up the Development Environment</a></li>
15          <li><a href="#alt-build">Using the ADK Alternative Build System</a></li>
16        </ol>
17      </li>
18      <li><a href="#adk-conn">How the ADK Connects with Android Devices</a>
19        <ol>
20          <li><a href="#adk-conn-bt">ADK Connection over Bluetooth</a></li>
21          <li><a href="#adk-conn-usb">ADK Connection over USB</a></li>
22        </ol>
23      </li>
24      <li><a href="#audio-dock">USB Audio Dock Implementation</a></li>
25    </ol>
26
27    <h2>See also</h2>
28    <ol>
29      <li><a href="aoa.html">Android Open Accessory Protocol</a></li>
30      <li><a href="aoa2.html">Android Open Accessory Protocol 2.0</a></li>
31      <li><a href="{@docRoot}guide/topics/connectivity/usb/accessory.html">USB Accessory Dev
32      Guide</a></li>
33    </ol>
34  </div>
35</div>
36
37<p>The Android Accessory Development Kit (ADK) for 2012 is the latest reference implementation of
38an <a href="aoa.html">Android Open Accessory</a> device, designed to help Android hardware accessory
39builders and software developers create accessories for Android. The ADK 2012 is based on the <a
40href="http://arduino.cc">Arduino</a> open source electronics prototyping platform, with some
41hardware and software extensions that allow it to communicate with Android devices.</p>
42
43<p>A limited number of these kits were produced and distributed at the Google I/O 2012 developer
44conference. If you did not receive one of these kits, fear not! The specifications and design files
45for the hardware were also released for use by manufacturers and hobbyists. You should expect to see
46kits with similar features available for purchase, or you can build one yourself!</p>
47
48<p>One of the important new features demonstrated by this ADK is the ability to play audio over a
49USB connection. Be sure to check out the <a href="#audio-dock">reference implementation</a> of a USB
50audio dock in this ADK if you are interested in making audio-related USB accessories for
51Android.</p>
52
53<h2 id="components">Components</h2>
54
55<p>The ADK 2012 is based on the Arduino open source electronics prototyping platform and is an open
56hardware design. The hardware design files and firmware source code are included with the ADK
57software download. The ADK contains two main physical hardware components:</p>
58
59<ol>
60  <li>Main processing board containing the microprocessor, USB connections, power connector and
61input/output pins. This board can be removed and used separately from the rest of the hardware.</li>
62  <li>Shield containing sensors, LEDs, input controls, audio amplifier and speaker output, contained
63in a custom, polygon box enclosure.</li>
64</ol>
65
66<p>The main hardware features of the ADK are as follows:</p>
67
68<ul>
69  <li>An ARM 32-bit Cortex M3 micro-processor</li>
70  <li>Separate USB connections for an Android device and computer connection for programming and
71debugging</li>
72  <li>Sensors for light, color, proximity, temperature, humidity, barometric pressure, and
73acceleration</li>
74  <li>Micro SD Card slot</li>
75  <li>Bluetooth support</li>
76</ul>
77
78<p>The ADK comes preloaded with an alarm clock firmware program that you can use immediately. A
79companion Android application, <a
80href="https://play.google.com/store/apps/details?id=com.google.android.apps.adk2">ADK 2012</a>, is
81available on Google Play. The source code for both the Android application and the ADK firmware (an
82Arduino sketch) can be downloaded from this page.</p>
83
84<p>The ADK 2012 also comes with additional parts to help you develop accessories with it,
85including:</p>
86
87<ul>
88  <li>AC power adapter</li>
89  <li>USB A to Micro USB B connector cable</li>
90  <li>Micro USB B to Micro USB AB connector (small, rectangular plug)</li>
91  <li>Micro SD Card, preinstalled in the ADK SD Card socket</li>
92</ul>
93
94<h2 id="clock">Using the Alarm Clock</h2>
95
96<p>An alarm clock program comes preloaded on the ADK. This firmware program allows you to use the
97ADK as an alarm clock.</p>
98
99<p>To use the ADK as an alarm clock:</p>
100
101<ol>
102  <li>Open up the ADK by gently squeezing the two widest faces of the enclosure.</li>
103  <li>Attach the provided AC power adapter (round connector) to the main ADK board, or attach a USB
104cable to the port marked <strong>Computer</strong> and a USB port on your computer.</li>
105  <li>Place and hold your fingertip over the clock symbol on the control face.
106    <p class="note"><strong>Note:</strong> You may need to hold your finger in place for 1-2
107seconds.</p>
108  </li>
109  <li>Use the plus (+) and minus (-) symbols inside the clock digits to set the correct time.</li>
110  <li>Place your fingertip over the alarm clock symbol to activate alarm setting.</li>
111  <li>Use the plus (+) and minus (-) symbols inside the clock digits to set the alarm time.</li>
112  <li>Use the plus (+) and minus (-) symbols inside the last two clock digits to turn the alarm on
113({@code on}) or off ({@code oF}).</li>
114  <li>To set the alarm tone, place and hold your fingertip over the alarm clock symbol, then tap the
115slider control on top of the enclosure.</li>
116</ol>
117
118<p>To use the <strong>ADK 2012</strong> companion application for the alarm clock:</p>
119
120<ol>
121  <li>Load the companion application on your Android device running Android 3.1 (API Level 12) or
122higher:
123    <ul>
124      <li>Using an NFC-enabled Android device, unlock and hold the device against the left side of
125the ADK enclosure. Follow the prompts to install the app.
126      <br>- or -</li>
127      <li>Start Google Play on your device, search for the <strong>ADK 2012</strong> application and
128install it. If you cannot find the app, your device is not compatible. Try installing on another
129device.</li>
130    </ul>
131  </li>
132  <li>Connect your Android device to the ADK using one of the following methods:
133    <ul>
134      <li id="conn-bt">To connect using Bluetooth:
135        <ol>
136          <li>Plug the AC power adapter into the ADK.</li>
137          <li>On your Android device, turn Bluetooth On (<strong>Settings >
138Bluetooth</strong>).</li>
139          <li>In the <strong>Settings</strong> page, press the <strong>Bluetooth</strong> option to
140view paired devices.</li>
141          <li>Select <strong>Search for Devices</strong> to locate the ADK 2012 accessory and follow
142the on screen instructions to connect.</li>
143          <li>After pairing is complete, start the <strong>ADK 2012</strong> app on your Android
144device.</li>
145          <li>On the start screen, select the <strong>Use Bluetooth</strong> button.</li>
146          <li>In the list of paired devices, select the <strong>ADK 2012</strong> device.</li>
147          <li>The <strong>ADK 2012</strong> app should switch to the menu screen and you can start
148interacting with the ADK accessory.</li>
149        </ol>
150      </li>
151
152      <li id="conn-usb">To connect using USB:
153        <ol>
154          <li>Plug the AC power adapter into the ADK.</li>
155          <li>Connect the Micro USB AB connector (small, rectangular plug) to the port labeled
156<strong>Phone</strong> on the ADK board.</li>
157          <li>Unlock your Android device and connect the Micro USB B connector to your device.
158            <p class="note"><strong>Note:</strong> Your device must support Android USB accessory
159mode. Devices that support this mode include Google Nexus devices.</p>
160          </li>
161          <li>On the Android device, you should see a prompt to connect to the <strong>ADK DemoKit
1622012</strong>, select <strong>OK</strong>.</li>
163          <li>The <strong>ADK 2012</strong> app should start automatically and you can start
164interacting with the ADK.</li>
165        </ol>
166      </li>
167    </ul>
168  </li>
169</ol>
170
171<p class="note"><strong>Note:</strong> When using the ADK with a USB connection to an Android
172device, make sure the AC power adapter is plugged in. A USB connection to a computer does not
173provide sufficient voltage to power both the ADK and a USB connection to a device.</p>
174
175
176<h2 id="play-audio">Playing Audio</h2>
177
178<p>The ADK 2012 comes with audio output capabilities, including an amplifier and speaker. You can
179use it to play audio from your Android device using either a Bluetooth or USB connection.</p>
180
181<p>To play audio over Bluetooth:</p>
182
183<ol>
184  <li>Follow the instructions in the <a href="#conn-bt">previous section</a> to connect your Android
185device to the ADK over Bluetooth.</li>
186  <li>On your Android device, navigate to the <strong>Settings > Bluetooth</strong> page to view the
187list of paired devices, and make sure the ADK is connected.</li>
188  <li>Select the settings icon next to the <strong>ADK 2012</strong> item.</li>
189  <li>Make sure the <strong>Media Audio</strong> option is enabled.</li>
190  <li>Navigate to an application that plays music or other audio.</li>
191  <li>Play a song or sound and listen to it on the ADK speaker!</li>
192</ol>
193
194<p>To play audio over USB, you must use a device running Android 4.1 (API Level 16) or higher:</p>
195
196<ol>
197  <li>Plug the AC power adapter into the ADK.</li>
198  <li>Connect the Micro USB AB connector (small, rectangular plug) to the Phone port on the ADK
199board.</li>
200  <li>Unlock your Android device and connect the Micro USB B connector to your device.
201    <p class="note"><strong>Note:</strong> Your device must support Android USB accessory
202mode. Devices that support this mode include Google Nexus devices.</p>
203  </li>
204  <li>On the Android device, you should see a prompt to connect to the <strong>ADK DemoKit
2052012</strong>, select <strong>Cancel</strong> and allow the ADK to connect as a media device
206only.</li>
207  <li>Navigate to an application that plays music or other audio.</li>
208  <li>Play a song or sound and listen to it on the ADK speaker!</li>
209</ol>
210
211<p class="note"><strong>Note:</strong> When using the ADK with a USB connection to an Android
212device, make sure the AC power adapter is plugged in. A USB connection to a computer does not
213provide sufficient voltage to power both the ADK and a USB connection to a device.</p>
214
215
216<h2 id="dev">Developing Accessories with ADK 2012</h2>
217
218<p>The ADK 2012 is a hardware platform and a set of software libraries for prototyping Android
219accessories. This section discusses how to set up a development environment for programming the ADK
220to make it do what you want and to test software for building your own Android accessories.</p>
221
222<h3 id="src-download">Downloading the ADK Source</h3>
223
224<p>The support software and hardware specifications for the ADK 2012 are available from the Android
225source repository. Follow the instructions below to obtain the source material for the ADK.</p>
226
227<p>To download the ADK 2012 software, source code and hardware design specifications.</p>
228
229<ol>
230  <li>Download and install <a href="http://git-scm.com/download">Git</a> for your development
231system.</li>
232  <li>Download and setup the {@code repo} tool, as described on the <a
233href="http://source.android.com/source/downloading.html#installing-repo">Android open source
234project</a> site.</li>
235  <li>In a terminal window, create a new directory for the downloaded source files, initialize and
236synchronize a local repository:
237<pre>
238$> mkdir android-accessories
239$> cd android-accessories
240$> repo init -u https://android.googlesource.com/accessories/manifest
241$> repo sync
242</pre>
243  </li>
244</ol>
245
246<p>After successfully completing this process, you should have the source code and tools for
247working with the ADK 2012:</p>
248
249<ul>
250  <li>{@code adk2012/board} - Source code and hardware design files for the ADK 2012</li>
251  <li>{@code adk2012/app} - Source code for the ADK 2012 Android companion application</li>
252  <li>{@code external/ide} - Source code for the ADK 2012 Integrated Development Environment
253(IDE)</li>
254  <li>{@code external/toolchain} - The toolchain used by the ADK 2012 IDE</li>
255</ul>
256
257
258<h3 id="dev-setup">Setting Up the Development Environment</h3>
259
260<p>The ADK 2012 comes with an integrated development environment (IDE) that you use to develop
261software and program the ADK 2012 accessory. The following instructions explain how to setup and run
262the ADK 2012 IDE.</p>
263
264<p>To set up and run the ADK 2012 IDE:</p>
265
266<ol>
267  <li>Download and install the Java Development Kit 6 or higher from <a
268    href="http://java.oracle.com">java.oracle.com</a>.</li>
269  <li>Download the ADK 2012 IDE for your development platform:
270    <ul>
271      <li><a href="https://dl-ssl.google.com/android/adk/adk2012_ide-win32-20120626.zip">
272          Windows</a></li>
273      <li><a href="https://dl-ssl.google.com/android/adk/adk2012_ide-macosx-20120626.zip">
274          Mac</a></li>
275      <li>Linux
276        <a href="https://dl-ssl.google.com/android/adk/adk2012_ide-linux32-20120626.tgz">32bit</a>,
277        <a href="https://dl-ssl.google.com/android/adk/adk2012_ide-linux64-20120626.tgz">64bit</a>
278      </li>
279    </ul>
280  </li>
281  <li>Unpack the downloaded archive.</li>
282  <li>Run the application by navigating to the unpacked {@code ADK2012_IDE/} folder and execute
283    the {@code arduino} file.</li>
284</ol>
285
286<p>After you have successfully installed and run the ADK 2012 IDE, you must configure it to use
287the ADK 2012 library.</p>
288
289<p>To configure the ADK 2012 IDE for use with the ADK libraries:</p>
290
291<ol>
292  <li>Start the ADK 2012 IDE and choose <strong>File > Preferences</strong>.</li>
293  <li>In the <strong>Preferences</strong> dialog, make a note of the <strong>Sketchbook
294location</strong> directory.</li>
295  <li>Copy the {@code &lt;adk-source-download&gt;/adk2012/board/library/ADK2} directory and its
296contents into your {@code sketchbook/libraries/} directory, so that you create a {@code
297sketchbook/libraries/ADK2} directory.</li>
298  <li>Stop and restart the <strong>ADK 2012 IDE</strong>.</li>
299  <li>In the IDE, choose <strong>File > Examples > ADK2</strong> and then choose one of the example
300sketches:
301    <ul>
302      <li><strong>clock</strong> - The sketch that is preloaded onto the ADK 2012.</li>
303      <li><strong>BluetoothScan</strong> - An example sketch demonstrating code that connects an
304accessory to an Android device over Bluetooth.</li>
305      <li><strong>usbaccessory</strong> - An example sketch demonstrating code that connects an
306accessory to an Android device through a USB cable.</li>
307    </ul>
308  </li>
309  <li>Connect a Micro USB cable from the <strong>Computer</strong> port on the ADK board to your
310development computer.</li>
311  <li>In the <strong>ADK 2012 IDE</strong>, establish a serial port connection with the ADK by
312selecting <strong>Tools > Serial Port</strong> and selecting the serial port for the ADK.</li>
313  <li>In the <strong>ADK 2012 IDE</strong>, choose the ADK by selecting<strong>Tools > Board >
314Google ADK2</strong>.</li>
315  <li>Modify an example sketch or create your own.</li>
316  <li>Upload the sketch to the ADK by choosing <strong>File > Upload</strong>. When the <strong>ADK
3172012 IDE</strong> reports <strong>Done uploading</strong>, the sketch is uploaded and the ADK is
318ready to communicate with your Android device.</li>
319</ol>
320
321<h3 id="alt-build">Using the ADK Alternative Build System</h3>
322
323<p>An alternative, make file-based build and upload system is also available for the ADK 2012. This
324system is command line based and intended for production environments where using an IDE environment
325to load software onto accessory hardware may be inconvenient or undesirable.</p>
326
327<p>To setup the environment:</p>
328<ol>
329  <li><a href="#src-download">Download</a> the ADK 2012 source code files.</li>
330  <li>In a terminal window, navigate to {@code
331&lt;adk-source-download&gt;/adk2012/board/MakefileBasedBuild}.</li>
332  <li>Execute the following command and follow the instructions:
333    <pre>$> ./setup</pre>
334  </li>
335</ol>
336
337<p>To build a program for your accessory:</p>
338<ol>
339  <li>Place your accessory code in the {@code MakefileBasedBuild/app} directory, including all
340required library files. See the {@code app/main.c} file for an example of the program format.</li>
341  <li>Execute the following command and follow the instructions:
342    <pre>$> ./build</pre>
343  </li>
344</ol>
345
346<p>To load the program on your accessory hardware:</p>
347<ol>
348  <li>Run the build process above and make sure your program compiled successfully.</li>
349  <li>Attach the accessory via USB cable to your development computer.</li>
350  <li>Check which port the accessory is attached to and modify the {@code UART} variable in the
351{@code flash} script to the correct port address. On linux machines, the port address is typically
352{@code /dev/ttyUSB0}.</li>
353  <li>Execute the following command to load the program on the accessory:
354  <pre>$> ./flash</pre></li>
355</ol>
356
357<h2 id="adk-conn">How the ADK Connects with Android Devices</h2>
358
359<p>The essential feature of any Android accessory is its ability to connect and communicate with an
360Android device. Creating a fast and reliable connection between your accessory and Android devices
361is the first order of business when building software for an accessory. This section describes the
362connection and communication essentials used in the ADK 2012 so that you can apply them to
363developing your own Android accessories.</p>
364
365<h3 id="adk-conn-bt">ADK Connection over Bluetooth</h3>
366
367<p>The ADK 2012 app and hardware accessory use a Bluetooth Serial Port Profile (SPP) connection to
368communicate. This connection allows two way communication between the ADK accessory and Android
369devices.</p>
370
371<p class="note"><strong>Note:</strong> The implementation of the ADK hardware allows the use of
372other profiles and multiple connections. However, the basic communication between the ADK 2012
373accessory and the Android application uses SPP.</p>
374
375<h4 id="acc-bt-code">Accessory Bluetooth Code</h4>
376
377<p>In order to enable Bluetooth communications, the {@code clock.ino} sketch for the ADK 2012
378accessory calls a {@code btStart()} method during the {@code setup()} method to enable radio
379frequency communications and start listening for Bluetooth connections:</p>
380
381<pre>
382ADK L;
383void setup() {
384 L.adkInit();
385 L.btStart();
386}
387...
388void btStart(){
389    uint8_t i, dlci;
390    int f;
391
392    L.btEnable(adkBtConnectionRequest, adkBtLinkKeyRequest, adkBtLinkKeyCreated,
393               adkBtPinRequest, NULL);
394
395    dlci = L.btRfcommReserveDlci(RFCOMM_DLCI_NEED_EVEN);
396
397    if(!dlci) dbgPrintf("BTADK: failed to allocate DLCI\n");
398    else{
399
400        //change descriptor to be valid...
401        for(i = 0, f = -1; i &lt; sizeof(sdpDescrADK); i++){
402
403            if(sdpDescrADK[i] == MAGIX){
404                if(f == -1) f = i;
405                else break;
406            }
407        }
408
409        if(i != sizeof(sdpDescrADK) || f == -1){
410
411            dbgPrintf("BTADK: failed to find a single marker in descriptor\n");
412            L.btRfcommReleaseDlci(dlci);
413            return;
414        }
415
416        sdpDescrADK[f] = dlci >> 1;
417
418        dbgPrintf("BTADK has DLCI %u\n", dlci);
419
420        L.btRfcommRegisterPort(dlci, btAdkPortOpen, btAdkPortClose, btAdkPortRx);
421        L.btSdpServiceDescriptorAdd(sdpDescrADK, sizeof(sdpDescrADK));
422    }
423}
424</pre>
425
426<p>Notice that the {@code sdpDescrADK} object contains a Universally Unique Identifier (UUID) in the
427variable {@code BT_ADK_UUID}. This identifier <em>must match</em> the device UUID provided in the
428{@link android.bluetooth.BluetoothSocket} connection request in the Android application code.</p>
429
430<p>Once Bluetooth is enabled with the code shown above, the accessory listens for connection
431requests. The ADK library handles listening and connection details, so the accessory calls
432{@code ADK::adkEventProcess()} once during each loop execution:</p>
433
434<pre>
435void loop(void)
436{
437  ...
438  L.adkEventProcess(); //let the adk framework do its thing
439  ...
440}
441</pre>
442
443<p>If a Bluetooth connection has been established, any commands are routed to the
444{@code btAdkPortRx()} callback method (which was registered with the ADK library as part of the
445{@code btStart()} method) and processed accordingly. The ADK accessory sends messages back through
446the Bluetooth connection using the {@code ADK::btRfcommPortTx()} method.
447For more details, review the implementations of these methods in the {@code clock.ino} sketch.</p>
448
449<h4 id="app-bt-code">Android App Bluetooth Code</h4>
450
451<p>In the ADK 2012 Android app, the code for handling Bluetooth connections is encapsulated in in a
452{@code BTConnection} class. In this class, the application requests access to the Bluetooth adapter
453and negotiates a connection with the ADK 2012 accessory. Here is a summary of the relevant code:</p>
454
455<pre>
456mAdapter = BluetoothAdapter.getDefaultAdapter();
457BluetoothDevice device = mAdapter.getRemoteDevice(address);
458mSocket = device.createInsecureRfcommSocketToServiceRecord(ADK_UUID);
459mSocket.connect();
460</pre>
461
462<p>Note the {@code ADK_UUID} parameter in the second line. This identifier must match the identifier
463output by the accessory (the {@code BT_ADK_UUID} variable mentioned earlier), otherwise the protocol
464negotiation fails and the {@link android.bluetooth.BluetoothSocket} is not created. Once a
465connection is established, you obtain {@link java.io.InputStream} and {@link java.io.OutputStream}
466objects from the socket to communicate with the accessory:</p>
467
468<pre>
469mInStream = mSocket.getInputStream();
470mOutStream = mSocket.getOutputStream();
471</pre>
472
473<p>Review the {@code BTConnection.java} file provided in the ADK 2012 software download for more
474implementation details.</p>
475
476<h3 id="adk-conn-usb">ADK Connection over USB</h3>
477
478<p>The ADK 2012 app and hardware accessory can also use a USB connection to communicate, similar to
479the original ADK.</p>
480
481<h4 id="acc-usb-code">Accessory USB Code</h4>
482
483<p>The ADK library takes care of most of the implementation details for a USB connection, the
484accessory code must make a few calls to initialize USB connectivity, including setting the accessory
485identification strings:</p>
486
487<pre>
488ADK L;
489void setup() {
490  L.adkInit();
491  L.usbSetAccessoryStringVendor(...);
492  L.usbSetAccessoryStringName(...);
493  L.usbSetAccessoryStringLongname(...);
494  L.usbSetAccessoryStringVersion(...);
495  L.usbSetAccessoryStringUrl(...);
496  L.usbSetAccessoryStringSerial(...);
497
498  L.usbStart();
499}
500</pre>
501
502<p class="note"><strong>Note:</strong> The identification strings must match the USB accessory
503filter settings specified in the connecting Android application,otherwise the application cannot
504connect with the accessory.</p>
505
506<p>Once USB is enabled with code shown above, the accessory listens for connection requests. The ADK
507library handles listening and connection details, so the accessory calls {@code
508ADK::adkEventProcess()} once during each loop execution:</p>
509
510<pre>
511void loop(void)
512{
513  ...
514  L.adkEventProcess(); //let the adk framework do its thing
515  ...
516}
517</pre>
518
519<p>The accessory must then check for a live USB connection to process commands and send
520messages. Here is a summary of the relevant code:</p>
521
522<pre>
523void loop() {
524  if (L.accessoryConnected()) {
525    int recvLen = L.accessoryReceive(msg, sizeof(msg));
526    if (recvLen > 0) {
527      ... // process message
528    }
529
530    L.accessorySend(outmsg, outmsgLen);
531  }
532  L.adkEventProcess();
533}
534</pre>
535
536<p>For more details, review the implementations of these methods in the {@code clock.ino}
537sketch.</p>
538
539<h4 id="app-usb-code">Android App USB Code</h4>
540
541<p>In the ADK 2012 Android app, the code for handling USB connections is encapsulated in a
542{@code UsbConnection} class. This class sets up a {@link android.content.BroadcastReceiver} to
543listen for USB events and then attempts to connect when a matching connection event is received.
544Here is a summary of the relevant code:</p>
545
546<pre>
547import com.android.future.usb.UsbAccessory;
548import com.android.future.usb.UsbManager;
549
550mUSBManager = UsbManager.getInstance(this);
551UsbAccessory acc = mUSBManager.getAccessoryList()[0];
552
553if (!mUSBManager.hasPermission(acc)) return;
554</pre>
555
556<p>The ADK 2012 app uses the support library to implement the USB accessory connections, in order to
557support devices running Android 2.3.4 (API Level 10). If you only need to support Android
5583.1 (API Level 12) and higher devices, you can replace the first 4 lines the following code:</p>
559
560<pre>
561import android.hardware.usb.UsbAccessory
562import android.hardware.usb.UsbManager
563
564mUSBManager = (UsbManager) getSystemService(Context.USB_SERVICE);
565UsbAccessory acc = (UsbAccessory)
566                   intent.getParcelableExtra(UsbManager.EXTRA_ACCESSORY);
567</pre>
568
569<p>Note that the app only receives events when the USB accessory identification information matches
570the information in the {@code res/xml/usb_accessory_filter.xml} file, referenced by the
571application’s manifest statement:</p>
572
573<pre>
574&lt;meta-data
575    android:name="android.hardware.usb.action.USB_ACCESSORY_ATTACHED"
576    android:resource="@xml/usb_accessory_filter" /&gt;
577</pre>
578
579<p>Connections from other USB devices are not received by the ADK 2012 accessory.</p>
580
581<p>Once the connection is established, the app can communicate with the accessory through file input
582and output streams, as shown in the following example code:</p>
583
584<pre>
585ParcelFileDescriptor mFD = mUSBManager.openAccessory(acc);
586if (mFD != null) {
587  FileDescripter fd = mFD.getFileDescriptor();
588  mIS = new FileInputStream(fd);  // use this to receive messages
589  mOS = new FileOutputStream(fd); // use this to send commands
590}
591</pre>
592
593<p>Review the {@code UsbConnection.java} file provided in the ADK 2012 source code for more
594implementation details.</p>
595
596<h2 id="audio-dock">USB Audio Dock Implementation</h2>
597
598<p>One of the important new features introduced with the ADK 2012 is the ability to play audio over
599a USB connection. This innovation was introduced as an update to Android Open Accessory (AOA)
600<a href="aoa2.html">protocol 2.0</a> and is available on devices running Android 4.1 (API Level 16)
601and higher.</p>
602
603<p>The ADK 2012 provides a reference implementation of this functionality for accessory developers.
604No software application is required to be installed on the connected Android device, accessory
605developers only need to support AOA v2. This implementation demonstrates audio output of 16bit,
60644.1kHz stereo PCM source data compressed into a single channel due to the audio hardware available
607on the accessory.</p>
608
609<p>Using the audio output features provided by the ADK library requires only a few function calls.
610The first few calls are in the accessory {@code setup()} routine, which prepare the accessory for
611USB connections and audio output, as summarized in the code example below:</p>
612
613<pre>
614ADK L;
615void setup() {
616  L.audioInit();
617  L.usbh_init()
618  L.usbStart();
619}
620</pre>
621
622<p>For more information about the {@code ADK::audioInit()} function, see the {@code
623libraries/ADK/Audio.c} library file. For more information about the {@code ADK::usbh_init()}
624function, see the {@code libraries/ADK/Usbh.c} library file.</p>
625
626<p>After completing this setup, the {@code loop()} function calls {@code ADK::adkEventProcess()} to
627handle audio output and other ADK functions:</p>
628
629<pre>
630void loop(void)
631{
632  ...
633  L.adkEventProcess(); //let the adk framework do its thing
634  ...
635}
636</pre>
637
638<p>This call executes task queuing for the ADK and as part of the execution process, the task queue
639executes {@code usbh_work()} in {@code libraries/ADK/Usbh.c}, which handles audio output requests.
640Review the implementation of this function for details. For additional implementation details on
641audio output, see the {@code libraries/ADK/accessory.c} library file.</p>
642