1 <html devsite> 2 <head> 3 <title>MIDI</title> 4 <meta name="project_path" value="/_project.yaml" /> 5 <meta name="book_path" value="/_book.yaml" /> 6 </head> 7 <body> 8 <!-- 9 Copyright 2017 The Android Open Source Project 10 11 Licensed under the Apache License, Version 2.0 (the "License"); 12 you may not use this file except in compliance with the License. 13 You may obtain a copy of the License at 14 15 http://www.apache.org/licenses/LICENSE-2.0 16 17 Unless required by applicable law or agreed to in writing, software 18 distributed under the License is distributed on an "AS IS" BASIS, 19 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 20 See the License for the specific language governing permissions and 21 limitations under the License. 22 --> 23 24 25 26 <p> 27 <a href="http://en.wikipedia.org/wiki/MIDI">MIDI</a> (Musical Instrument Digital Interface) 28 is a standard protocol for inter-connecting computers with musical instruments, stage lighting, 29 and other time-oriented media. 30 </p> 31 32 <p> 33 Strictly speaking, MIDI is unrelated to audio. But since MIDI is commonly used with 34 music, this article is placed in the audio section. 35 </p> 36 37 <h2 id="transports">Transports</h2> 38 39 <p> 40 The physical <a href="http://en.wikipedia.org/wiki/Transport_layer">transport layer</a> 41 specified in original MIDI 1.0 is a current loop with 42 <a href="http://en.wikipedia.org/wiki/DIN_connector">5-pin DIN</a> connector. 43 </p> 44 45 <p> 46 Since MIDI 1.0, additional transports have been defined, including MIDI over USB 47 and a proposed draft for MIDI over 48 <a href="http://en.wikipedia.org/wiki/Bluetooth_low_energy">Bluetooth Low Energy</a> (BLE). 49 </p> 50 51 <h2 id="for-android">MIDI for Android</h2> 52 53 <p> 54 Android 3.1 and later support 55 <a href="http://en.wikipedia.org/wiki/USB_On-The-Go">USB On-The-Go</a>, 56 which permits an Android device to act as USB host to drive USB 57 peripherals. The USB host mode APIs introduced in Android 3.1 permit 58 developers to implement MIDI over USB at the application level, but until 59 recently there have been no built-in platform APIs for MIDI. 60 </p> 61 62 <p> 63 Beginning with the Android 6.0 (Marshmallow) release, device makers can enable optional MIDI support in the platform. 64 Android directly supports USB, draft BLE, and virtual (inter-app) transports. 65 Android indirectly supports MIDI 1.0 via an external adapter. 66 </p> 67 68 <p> 69 For details on application programming with the new MIDI APIs, see the 70 <a href="https://developer.android.com/reference/android/media/midi/package-summary.html"><code>android.media.midi</code></a> 71 package. 72 </p> 73 74 <p> 75 The remainder of this article discusses how an Android device maker can 76 enable MIDI support in the platform. 77 </p> 78 79 <h2 id="transport">Enabling transports</h2> 80 81 <p> 82 The implementation depends on ALSA for USB host mode and USB peripheral mode transports. 83 ALSA is not used for the BLE and virtual transports. 84 </p> 85 86 <h3 id="usb-host">USB host mode</h3> 87 88 <p> 89 To enable MIDI for USB host mode, first support USB host mode in general, and 90 then enable <code>CONFIG_SND_RAWMIDI</code> and <code>CONFIG_SND_USB_MIDI</code> in your kernel configuration. 91 See <a href="/devices/tech/config/kernel.html">Android Kernel Configuration.</a> 92 </p> 93 94 <p> 95 The MIDI over USB transport is formally defined by the 96 <a href="http://www.usb.org/developers/docs/devclass_docs/midi10.pdf"> 97 Universal Serial Bus Device Class Definition for MIDI Devices Release 1.0 Nov 1, 1999</a> 98 standard published by the 99 <a href="http://www.usb.org/">USB Implementers Forum, Inc</a>. 100 </p> 101 102 <h3 id="usb-peripheral">USB peripheral mode</h3> 103 104 <p> 105 To enable MIDI for USB peripheral mode, you may need to apply patches 106 to your Linux kernel to integrate the 107 <code>drivers/usb/gadget/f_midi.c</code> into the USB gadget 108 driver. As of this writing, these patches are available for Linux kernel version 109 3.10. These patches have not yet been updated for 110 <a href="http://en.wikipedia.org/wiki/Configfs">ConfigFs</a> 111 (a new architecture 112 for USB gadget drivers), nor are they merged at upstream 113 <a href="http://kernel.org">kernel.org</a>. 114 </p> 115 116 <p> 117 The patches are shown in commit order for the kernel tree at project <code>kernel/common</code> 118 branch <code>android-3.10</code>: 119 </p> 120 <ol> 121 <li><a href="https://android-review.googlesource.com/#/c/127450/">https://android-review.googlesource.com/#/c/127450/</a></li> 122 <li><a href="https://android-review.googlesource.com/#/c/127452/">https://android-review.googlesource.com/#/c/127452/</a></li> 123 <li><a href="https://android-review.googlesource.com/#/c/143714/">https://android-review.googlesource.com/#/c/143714/</a></li> 124 </ol> 125 126 <p> 127 In addition, the end user must also check the box for MIDI 128 in the <em>Settings / Developer options / Networking / Select USB Configuration</em> dialog, 129 or by pulling down from the top of screen while attached 130 to the USB host, selecting entry "USB for ...", and then choosing <strong>MIDI</strong>. 131 </p> 132 133 <h3 id="ble">BLE</h3> 134 135 <p> 136 MIDI over BLE is always enabled, provided the device supports BLE. 137 As this transport is in draft status, it is subject to change. 138 </p> 139 140 <h3 id="virtual">Virtual (inter-app)</h3> 141 142 <p> 143 The virtual (inter-app) transport is always enabled. 144 </p> 145 146 <h2 id="claim-feature">Claiming the feature</h2> 147 148 <p> 149 Applications can screen for the presence of MIDI support using the 150 <code>android.software.midi</code> feature. 151 </p> 152 153 <p> 154 To claim MIDI support, add this line to your <code>device.mk</code>: 155 </p> 156 <pre class="devsite-click-to-copy"> 157 PRODUCT_COPY_FILES += \ 158 frameworks/native/data/etc/android.software.midi.xml:system/etc/permissions/android.software.midi.xml 159 </pre> 160 161 <p> 162 See the 163 <a href="/compatibility/android-cdd.pdf">Android Compatibility Definition Document (CDD)</a> 164 for information 165 on requirements to claim the feature. 166 </p> 167 168 <h2 id="hostDebugging">Debugging while in host mode</h2> 169 170 <p> 171 While in USB host mode, Android Debug Bridge (adb) debugging over USB is unavailable. 172 See section <a href="http://developer.android.com/tools/help/adb.html#wireless">Wireless usage</a> 173 of 174 <a href="http://developer.android.com/tools/help/adb.html">Android Debug Bridge</a> 175 for an alternative. 176 </p> 177 178 </body> 179 </html> 180
