1 page.title=HDMI-CEC Control Service 2 @jd:body 3 4 <!-- 5 Copyright 2014 The Android Open Source Project 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18 --> 19 <div id="qv-wrapper"> 20 <div id="qv"> 21 <h2>In this document</h2> 22 <ol id="auto-toc"> 23 </ol> 24 </div> 25 </div> 26 27 <h2 id=intro>Introduction</h2> 28 29 <p>The High-Definition Multimedia Interface Consumer Electronics Control (HDMI-CEC) standard allows mulitmedia consumer products to communicate and 30 exchange information with each other. HDMI-CEC supports many features, like 31 Remote Control Passthrough and System Audio Control, but one of the most 32 popular is One Touch Play. One Touch Play lets a media source device turn on 33 the TV and switch its input port automatically, so you dont have to search for 34 the TV remote to switch from your Chromecast to Blu-ray player.</p> 35 36 <p>Most manufacturers have adopted HDMI-CEC so their devices work with other 37 companies devices. But because each manufacturer implements the HDMI-CEC 38 standard in different ways, devices dont always understand each other and 39 supported features vary between devices. Because of this variance, consumers 40 cant safely assume that two products that claim CEC support are completely 41 compatible.</p> 42 43 <h2 id=solution>Solution</h2> 44 45 46 <p>With the introduction of the Android TV Input Framework (TIF), HDMI-CEC brings 47 together all connected devices and minimizes compatibility issues. Android has 48 created a system service called <code>HdmiControlService</code> to alleviate these pain points.</p> 49 50 <p>By offering <code>HdmiControlService</code> as a part of the Android ecosystem, Android hopes to provide:</p> 51 52 <ul> 53 <li>A standard implementation of HDMI-CEC for all manufacturers, which will reduce 54 device incompatibility. Previously, manufacturers had to develop their own 55 implementations of HDMI-CEC or use third-party solutions.</li> 56 <li>A service that is well-tested against numerous HDMI-CEC devices already in the 57 market. Android has been conducting rigorous research on compatibility issues 58 found among the products and collecting useful advice from partners experienced 59 in the technology. The CEC service is designed to keep a healthy balance 60 between the standard and modifications to that standard so that it works with 61 the products that people already use.</li> 62 </ul> 63 64 <h2 id=overall_design>Overall design</h2> 65 66 67 <p><code>HdmiControlService</code> is connected with the rest of the system like TV Input Framework (TIF), Audio service, and Power service to implement the various features the standard 68 specifies.</p> 69 70 <p>See the following diagram for a depiction of the switch from a custom CEC 71 controller to an implementation of the simpler HDMI-CEC hardware abstraction 72 layer (HAL).</p> 73 74 <img src="images/HDMI_Control_Service.png" alt="Diagram that shows how HDMI-CEC was implemented before and after Android 5.0"> 75 76 <p class="img-caption"><strong>Figure 1.</strong> HDMI Control Service replacement</p> 77 78 <h2 id=implementation>Implementation</h2> 79 80 81 <p>See the following diagram for a detailed view of the HDMI control service.</p> 82 83 <img src="images/HDMI_Control_Service_Flow.png" alt="Image that shows how HDMI Control service details"> 84 85 <p class="img-caption"><strong>Figure 2.</strong> HDMI Control Service details</p> 86 87 <p>Here are the key ingredients to a proper Android HDMI-CEC implementation:</p> 88 89 <ul> 90 <li> A manager class <code>HdmiControlManager</code> provides priviledged apps with the API. System services like TV Input Manager service and Audio service can grab the service directly.</li> 91 <li> The service is designed to allow hosting more than one type of logical device.</li> 92 <li> HDMI-CEC is connected with the hardware via a hardware abstraction layer (HAL) 93 to simplify handling differences of the protocol and signalling mechanisms 94 between the devices. The HAL definition is available for device manufacturers 95 to use to implement the HAL layer.</li> 96 </ul> 97 98 <p class="note"><strong>Note</strong>: Device manufacturers should add the following line into <code>PRODUCT_COPY_FILES</code> in <code>device.mk</code>.</p> 99 100 <pre> 101 PRODUCT_COPY_FILES += \ 102 frameworks/native/data/etc/android.hardware.hdmi.cec.xml:system/etc/permissions/android.hardware.hdmi.cec.xml 103 </pre> 104 105 106 <p>Depending on whether your device is a HDMI sink device or a HDMI source device, 107 device manufactureres need to set <code>ro.hdmi.device_type</code> in <code>device.mk</code> for <code>HdmiControlService</code> to work correctly.</p> 108 109 <p>For HDMI source devices, like Over the Top (OTT) boxes, set:</p> 110 111 <pre> 112 PRODUCT_PROPERTY_OVERRIDES += ro.hdmi.device_type=<strong>4</strong> 113 </pre> 114 115 <p>For HDMI sink devices, like panel TVs, set:</p> 116 117 <pre> 118 PRODUCT_PROPERTY_OVERRIDES += ro.hdmi.device_type=<strong>0</strong></pre> 119 </p> 120 121 122 <ul> 123 <li> A device manufacturer-provided proprietary CEC controller cannot coexist with <code>HdmiControlService</code>. It must be disabled or removed. Common requirements for this come from the need to handle manufacturer-specific commands. The manufacturer-specific 124 command handler should be incorporated into the service by extending/modifying 125 it. This work is left to the device manufacturer and not specified by Android. 126 Note that any change made in the service for manufacturer-specific commands 127 must not interfere with the way standard commands are handled or the device 128 will not be Android compatible.</li> 129 <li> Access to the HDMI-CEC service is guarded with the protection level <code>SignatureOrSystem</code>. Only system components or the apps placed in <code>/system/priv-app</code> can access the service. This is to protect the service from abuse by apps with malicous intent.</li> 130 </ul> 131 132 <p>Android supports type <code>TV/Display(0)</code> and <code>playback device(4)</code>, which can issue the One Touch Play command to display. The other types (tuner 133 and recorder) are currently not supported.</p> 134 135 <h2 id=hdmi-cec_hal_definition>HDMI-CEC HAL definition</h2> 136 137 138 <p>In order to have the service in action, the HDMI-CEC HAL needs to be 139 implemented to the definition provided by Android. It abstracts differences in 140 the hardware level and exposes the primitive operations (allocate/read/write, 141 etc.) to the upper layer through API.</p> 142 143 <p>The API calls that device manufacturers must support are:</p> 144 145 <h3 id=tx_rx_events>TX/RX/Events</h3> 146 <ul> 147 <li><code>send_message</code></li> 148 <li><code>register_event_callback</code></li> 149 </ul> 150 151 <h3 id=info>Info</h3> 152 <ul> 153 <li><code>get_physical_address</code></li> 154 <li><code>get_version</code></li> 155 <li><code>get_vendor_id</code></li> 156 <li><code>get_port_info</code></li> 157 </ul> 158 159 <h3 id=logical_address>Logical Address</h3> 160 <ul> 161 <li><code>add_logical_address</code></li> 162 <li><code>clear_logical_address</code></li> 163 </ul> 164 165 <h3 id=status>Status</h3> 166 <ul> 167 <li><code>is_connected set_option</code></li> 168 <li><code>set_audio_return_channel</code></li> 169 </ul> 170 171 <p>Here is an excerpt of the HDMI-CEC HAL definition regarding APIs:</p> 172 173 <pre> 174 #ifndef ANDROID_INCLUDE_HARDWARE_HDMI_CEC_H 175 #define ANDROID_INCLUDE_HARDWARE_HDMI_CEC_H 176 177 ... 178 179 /* 180 * HDMI-CEC HAL interface definition. 181 */ 182 typedef struct hdmi_cec_device { 183 /** 184 * Common methods of the HDMI-CEC device. This *must* be the first member of 185 * hdmi_cec_device as users of this structure will cast a hw_device_t to hdmi_cec_device 186 * pointer in contexts where it's known the hw_device_t references a hdmi_cec_device. 187 */ 188 struct hw_device_t common; 189 190 /* 191 * (*add_logical_address)() passes the logical address that will be used 192 * in this system. 193 * 194 * HAL may use it to configure the hardware so that the CEC commands addressed 195 * the given logical address can be filtered in. This method can be called 196 * as many times as necessary in order to support multiple logical devices. 197 * addr should be in the range of valid logical addresses for the call 198 * to succeed. 199 * 200 * Returns 0 on success or -errno on error. 201 */ 202 int (*add_logical_address)(const struct hdmi_cec_device* dev, cec_logical_address_t addr); 203 204 /* 205 * (*clear_logical_address)() tells HAL to reset all the logical addresses. 206 * 207 * It is used when the system doesn't need to process CEC command any more, 208 * hence to tell HAL to stop receiving commands from the CEC bus, and change 209 * the state back to the beginning. 210 */ 211 void (*clear_logical_address)(const struct hdmi_cec_device* dev); 212 213 /* 214 * (*get_physical_address)() returns the CEC physical address. The 215 * address is written to addr. 216 * 217 * The physical address depends on the topology of the network formed 218 * by connected HDMI devices. It is therefore likely to change if the cable 219 * is plugged off and on again. It is advised to call get_physical_address 220 * to get the updated address when hot plug event takes place. 221 * 222 * Returns 0 on success or -errno on error. 223 */ 224 int (*get_physical_address)(const struct hdmi_cec_device* dev, uint16_t* addr); 225 226 /* 227 * (*send_message)() transmits HDMI-CEC message to other HDMI device. 228 * 229 * The method should be designed to return in a certain amount of time not 230 * hanging forever, which can happen if CEC signal line is pulled low for 231 * some reason. HAL implementation should take the situation into account 232 * so as not to wait forever for the message to get sent out. 233 * 234 * It should try retransmission at least once as specified in the standard. 235 * 236 * Returns error code. See HDMI_RESULT_SUCCESS, HDMI_RESULT_NACK, and 237 * HDMI_RESULT_BUSY. 238 */ 239 int (*send_message)(const struct hdmi_cec_device* dev, const cec_message_t*); 240 241 /* 242 * (*register_event_callback)() registers a callback that HDMI-CEC HAL 243 * can later use for incoming CEC messages or internal HDMI events. 244 * When calling from C++, use the argument arg to pass the calling object. 245 * It will be passed back when the callback is invoked so that the context 246 * can be retrieved. 247 */ 248 void (*register_event_callback)(const struct hdmi_cec_device* dev, 249 event_callback_t callback, void* arg); 250 251 /* 252 * (*get_version)() returns the CEC version supported by underlying hardware. 253 */ 254 void (*get_version)(const struct hdmi_cec_device* dev, int* version); 255 256 /* 257 * (*get_vendor_id)() returns the identifier of the vendor. It is 258 * the 24-bit unique company ID obtained from the IEEE Registration 259 * Authority Committee (RAC). 260 */ 261 void (*get_vendor_id)(const struct hdmi_cec_device* dev, uint32_t* vendor_id); 262 263 /* 264 * (*get_port_info)() returns the hdmi port information of underlying hardware. 265 * info is the list of HDMI port information, and 'total' is the number of 266 * HDMI ports in the system. 267 */ 268 void (*get_port_info)(const struct hdmi_cec_device* dev, 269 struct hdmi_port_info* list[], int* total); 270 271 /* 272 * (*set_option)() passes flags controlling the way HDMI-CEC service works down 273 * to HAL implementation. Those flags will be used in case the feature needs 274 * update in HAL itself, firmware or microcontroller. 275 */ 276 void (*set_option)(const struct hdmi_cec_device* dev, int flag, int value); 277 278 /* 279 * (*set_audio_return_channel)() configures ARC circuit in the hardware logic 280 * to start or stop the feature. Flag can be either 1 to start the feature 281 * or 0 to stop it. 282 * 283 * Returns 0 on success or -errno on error. 284 */ 285 void (*set_audio_return_channel)(const struct hdmi_cec_device* dev, int flag); 286 287 /* 288 * (*is_connected)() returns the connection status of the specified port. 289 * Returns HDMI_CONNECTED if a device is connected, otherwise HDMI_NOT_CONNECTED. 290 * The HAL should watch for +5V power signal to determine the status. 291 */ 292 int (*is_connected)(const struct hdmi_cec_device* dev, int port); 293 294 /* Reserved for future use to maximum 16 functions. Must be NULL. */ 295 void* reserved[16 - 11]; 296 } hdmi_cec_device_t; 297 298 #endif /* ANDROID_INCLUDE_HARDWARE_HDMI_CEC_H */ 299 </pre> 300 301 302 <p>The API lets the service make use of the hardware resource to send/receive 303 HDMI-CEC commands, configure necessary settings, and (optionally) communicate 304 with the microprocessor in the underlying platform that will take over the CEC 305 control while the Android system is in standby mode.</p> 306 307 <h2 id=testing>Testing</h2> 308 309 310 <p>Device manufacturers must test the APIs of the HDMI-CEC HAL with their own 311 tools to make sure they provide expected functionality.</p> 312
