cec-ioc-receive.rst (15568B)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: CEC 3 4.. _CEC_TRANSMIT: 5.. _CEC_RECEIVE: 6 7*********************************** 8ioctls CEC_RECEIVE and CEC_TRANSMIT 9*********************************** 10 11Name 12==== 13 14CEC_RECEIVE, CEC_TRANSMIT - Receive or transmit a CEC message 15 16Synopsis 17======== 18 19.. c:macro:: CEC_RECEIVE 20 21``int ioctl(int fd, CEC_RECEIVE, struct cec_msg *argp)`` 22 23.. c:macro:: CEC_TRANSMIT 24 25``int ioctl(int fd, CEC_TRANSMIT, struct cec_msg *argp)`` 26 27Arguments 28========= 29 30``fd`` 31 File descriptor returned by :c:func:`open()`. 32 33``argp`` 34 Pointer to struct cec_msg. 35 36Description 37=========== 38 39To receive a CEC message the application has to fill in the 40``timeout`` field of struct :c:type:`cec_msg` and pass it to 41:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 42If the file descriptor is in non-blocking mode and there are no received 43messages pending, then it will return -1 and set errno to the ``EAGAIN`` 44error code. If the file descriptor is in blocking mode and ``timeout`` 45is non-zero and no message arrived within ``timeout`` milliseconds, then 46it will return -1 and set errno to the ``ETIMEDOUT`` error code. 47 48A received message can be: 49 501. a message received from another CEC device (the ``sequence`` field will 51 be 0, ``tx_status`` will be 0 and ``rx_status`` will be non-zero). 522. the transmit result of an earlier non-blocking transmit (the ``sequence`` 53 field will be non-zero, ``tx_status`` will be non-zero and ``rx_status`` 54 will be 0). 553. the reply to an earlier non-blocking transmit (the ``sequence`` field will 56 be non-zero, ``tx_status`` will be 0 and ``rx_status`` will be non-zero). 57 58To send a CEC message the application has to fill in the struct 59:c:type:`cec_msg` and pass it to :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. 60The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is only available if 61``CEC_CAP_TRANSMIT`` is set. If there is no more room in the transmit 62queue, then it will return -1 and set errno to the ``EBUSY`` error code. 63The transmit queue has enough room for 18 messages (about 1 second worth 64of 2-byte messages). Note that the CEC kernel framework will also reply 65to core messages (see :ref:`cec-core-processing`), so it is not a good 66idea to fully fill up the transmit queue. 67 68If the file descriptor is in non-blocking mode then the transmit will 69return 0 and the result of the transmit will be available via 70:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` once the transmit has finished. 71If a non-blocking transmit also specified waiting for a reply, then 72the reply will arrive in a later message. The ``sequence`` field can 73be used to associate both transmit results and replies with the original 74transmit. 75 76Normally calling :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` when the physical 77address is invalid (due to e.g. a disconnect) will return ``ENONET``. 78 79However, the CEC specification allows sending messages from 'Unregistered' to 80'TV' when the physical address is invalid since some TVs pull the hotplug detect 81pin of the HDMI connector low when they go into standby, or when switching to 82another input. 83 84When the hotplug detect pin goes low the EDID disappears, and thus the 85physical address, but the cable is still connected and CEC still works. 86In order to detect/wake up the device it is allowed to send poll and 'Image/Text 87View On' messages from initiator 0xf ('Unregistered') to destination 0 ('TV'). 88 89.. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{12.8cm}| 90 91.. c:type:: cec_msg 92 93.. cssclass:: longtable 94 95.. flat-table:: struct cec_msg 96 :header-rows: 0 97 :stub-columns: 0 98 :widths: 1 1 16 99 100 * - __u64 101 - ``tx_ts`` 102 - Timestamp in ns of when the last byte of the message was transmitted. 103 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access 104 the same clock from userspace use :c:func:`clock_gettime`. 105 * - __u64 106 - ``rx_ts`` 107 - Timestamp in ns of when the last byte of the message was received. 108 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access 109 the same clock from userspace use :c:func:`clock_gettime`. 110 * - __u32 111 - ``len`` 112 - The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in 113 by the application. The driver will fill this in for 114 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be 115 filled in by the driver with the length of the reply message if ``reply`` was set. 116 * - __u32 117 - ``timeout`` 118 - The timeout in milliseconds. This is the time the device will wait 119 for a message to be received before timing out. If it is set to 0, 120 then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 121 If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, 122 then it will be replaced by 1000 if the ``reply`` is non-zero or 123 ignored if ``reply`` is 0. 124 * - __u32 125 - ``sequence`` 126 - A non-zero sequence number is automatically assigned by the CEC framework 127 for all transmitted messages. It is used by the CEC framework when it queues 128 the transmit result for a non-blocking transmit. This allows the application 129 to associate the received message with the original transmit. 130 131 In addition, if a non-blocking transmit will wait for a reply (ii.e. ``timeout`` 132 was not 0), then the ``sequence`` field of the reply will be set to the sequence 133 value of the original transmit. This allows the application to associate the 134 received message with the original transmit. 135 * - __u32 136 - ``flags`` 137 - Flags. See :ref:`cec-msg-flags` for a list of available flags. 138 * - __u8 139 - ``msg[16]`` 140 - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the 141 application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 142 For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with 143 the payload of the reply message if ``timeout`` was set. 144 * - __u8 145 - ``reply`` 146 - Wait until this message is replied. If ``reply`` is 0 and the 147 ``timeout`` is 0, then don't wait for a reply but return after 148 transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 149 The case where ``reply`` is 0 (this is the opcode for the Feature Abort 150 message) and ``timeout`` is non-zero is specifically allowed to make it 151 possible to send a message and wait up to ``timeout`` milliseconds for a 152 Feature Abort reply. In this case ``rx_status`` will either be set 153 to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or 154 :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`. 155 156 If the transmitter message is ``CEC_MSG_INITIATE_ARC`` then the ``reply`` 157 values ``CEC_MSG_REPORT_ARC_INITIATED`` and ``CEC_MSG_REPORT_ARC_TERMINATED`` 158 are processed differently: either value will match both possible replies. 159 The reason is that the ``CEC_MSG_INITIATE_ARC`` message is the only CEC 160 message that has two possible replies other than Feature Abort. The 161 ``reply`` field will be updated with the actual reply so that it is 162 synchronized with the contents of the received message. 163 * - __u8 164 - ``rx_status`` 165 - The status bits of the received message. See 166 :ref:`cec-rx-status` for the possible status values. 167 * - __u8 168 - ``tx_status`` 169 - The status bits of the transmitted message. See 170 :ref:`cec-tx-status` for the possible status values. 171 When calling :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` in non-blocking mode, 172 this field will be 0 if the transmit started, or non-0 if the transmit 173 result is known immediately. The latter would be the case when attempting 174 to transmit a Poll message to yourself. That results in a 175 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` without ever actually 176 transmitting the Poll message. 177 * - __u8 178 - ``tx_arb_lost_cnt`` 179 - A counter of the number of transmit attempts that resulted in the 180 Arbitration Lost error. This is only set if the hardware supports 181 this, otherwise it is always 0. This counter is only valid if the 182 :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set. 183 * - __u8 184 - ``tx_nack_cnt`` 185 - A counter of the number of transmit attempts that resulted in the 186 Not Acknowledged error. This is only set if the hardware supports 187 this, otherwise it is always 0. This counter is only valid if the 188 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set. 189 * - __u8 190 - ``tx_low_drive_cnt`` 191 - A counter of the number of transmit attempts that resulted in the 192 Arbitration Lost error. This is only set if the hardware supports 193 this, otherwise it is always 0. This counter is only valid if the 194 :ref:`CEC_TX_STATUS_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set. 195 * - __u8 196 - ``tx_error_cnt`` 197 - A counter of the number of transmit errors other than Arbitration 198 Lost or Not Acknowledged. This is only set if the hardware 199 supports this, otherwise it is always 0. This counter is only 200 valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set. 201 202.. tabularcolumns:: |p{6.2cm}|p{1.0cm}|p{10.1cm}| 203 204.. _cec-msg-flags: 205 206.. flat-table:: Flags for struct cec_msg 207 :header-rows: 0 208 :stub-columns: 0 209 :widths: 3 1 4 210 211 * .. _`CEC-MSG-FL-REPLY-TO-FOLLOWERS`: 212 213 - ``CEC_MSG_FL_REPLY_TO_FOLLOWERS`` 214 - 1 215 - If a CEC transmit expects a reply, then by default that reply is only sent to 216 the filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. If this 217 flag is set, then the reply is also sent to all followers, if any. If the 218 filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is also a 219 follower, then that filehandle will receive the reply twice: once as the 220 result of the :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, and once via 221 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 222 223 * .. _`CEC-MSG-FL-RAW`: 224 225 - ``CEC_MSG_FL_RAW`` 226 - 2 227 - Normally CEC messages are validated before transmitting them. If this 228 flag is set when :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is called, 229 then no validation takes place and the message is transmitted as-is. 230 This is useful when debugging CEC issues. 231 This flag is only allowed if the process has the ``CAP_SYS_RAWIO`` 232 capability. If that is not set, then the ``EPERM`` error code is 233 returned. 234 235.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{10.8cm}| 236 237.. _cec-tx-status: 238 239.. flat-table:: CEC Transmit Status 240 :header-rows: 0 241 :stub-columns: 0 242 :widths: 3 1 16 243 244 * .. _`CEC-TX-STATUS-OK`: 245 246 - ``CEC_TX_STATUS_OK`` 247 - 0x01 248 - The message was transmitted successfully. This is mutually 249 exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`. 250 Other bits can still be set if earlier attempts met with failure before 251 the transmit was eventually successful. 252 * .. _`CEC-TX-STATUS-ARB-LOST`: 253 254 - ``CEC_TX_STATUS_ARB_LOST`` 255 - 0x02 256 - CEC line arbitration was lost, i.e. another transmit started at the 257 same time with a higher priority. Optional status, not all hardware 258 can detect this error condition. 259 * .. _`CEC-TX-STATUS-NACK`: 260 261 - ``CEC_TX_STATUS_NACK`` 262 - 0x04 263 - Message was not acknowledged. Note that some hardware cannot tell apart 264 a 'Not Acknowledged' status from other error conditions, i.e. the result 265 of a transmit is just OK or FAIL. In that case this status will be 266 returned when the transmit failed. 267 * .. _`CEC-TX-STATUS-LOW-DRIVE`: 268 269 - ``CEC_TX_STATUS_LOW_DRIVE`` 270 - 0x08 271 - Low drive was detected on the CEC bus. This indicates that a 272 follower detected an error on the bus and requests a 273 retransmission. Optional status, not all hardware can detect this 274 error condition. 275 * .. _`CEC-TX-STATUS-ERROR`: 276 277 - ``CEC_TX_STATUS_ERROR`` 278 - 0x10 279 - Some error occurred. This is used for any errors that do not fit 280 ``CEC_TX_STATUS_ARB_LOST`` or ``CEC_TX_STATUS_LOW_DRIVE``, either because 281 the hardware could not tell which error occurred, or because the hardware 282 tested for other conditions besides those two. Optional status. 283 * .. _`CEC-TX-STATUS-MAX-RETRIES`: 284 285 - ``CEC_TX_STATUS_MAX_RETRIES`` 286 - 0x20 287 - The transmit failed after one or more retries. This status bit is 288 mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`. 289 Other bits can still be set to explain which failures were seen. 290 * .. _`CEC-TX-STATUS-ABORTED`: 291 292 - ``CEC_TX_STATUS_ABORTED`` 293 - 0x40 294 - The transmit was aborted due to an HDMI disconnect, or the adapter 295 was unconfigured, or a transmit was interrupted, or the driver 296 returned an error when attempting to start a transmit. 297 * .. _`CEC-TX-STATUS-TIMEOUT`: 298 299 - ``CEC_TX_STATUS_TIMEOUT`` 300 - 0x80 301 - The transmit timed out. This should not normally happen and this 302 indicates a driver problem. 303 304.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{10.8cm}| 305 306.. _cec-rx-status: 307 308.. flat-table:: CEC Receive Status 309 :header-rows: 0 310 :stub-columns: 0 311 :widths: 3 1 16 312 313 * .. _`CEC-RX-STATUS-OK`: 314 315 - ``CEC_RX_STATUS_OK`` 316 - 0x01 317 - The message was received successfully. 318 * .. _`CEC-RX-STATUS-TIMEOUT`: 319 320 - ``CEC_RX_STATUS_TIMEOUT`` 321 - 0x02 322 - The reply to an earlier transmitted message timed out. 323 * .. _`CEC-RX-STATUS-FEATURE-ABORT`: 324 325 - ``CEC_RX_STATUS_FEATURE_ABORT`` 326 - 0x04 327 - The message was received successfully but the reply was 328 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message 329 was the reply to an earlier transmitted message. 330 * .. _`CEC-RX-STATUS-ABORTED`: 331 332 - ``CEC_RX_STATUS_ABORTED`` 333 - 0x08 334 - The wait for a reply to an earlier transmitted message was aborted 335 because the HDMI cable was disconnected, the adapter was unconfigured 336 or the :ref:`CEC_TRANSMIT <CEC_RECEIVE>` that waited for a 337 reply was interrupted. 338 339 340Return Value 341============ 342 343On success 0 is returned, on error -1 and the ``errno`` variable is set 344appropriately. The generic error codes are described at the 345:ref:`Generic Error Codes <gen-errors>` chapter. 346 347The :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` can return the following 348error codes: 349 350EAGAIN 351 No messages are in the receive queue, and the filehandle is in non-blocking mode. 352 353ETIMEDOUT 354 The ``timeout`` was reached while waiting for a message. 355 356ERESTARTSYS 357 The wait for a message was interrupted (e.g. by Ctrl-C). 358 359The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` can return the following 360error codes: 361 362ENOTTY 363 The ``CEC_CAP_TRANSMIT`` capability wasn't set, so this ioctl is not supported. 364 365EPERM 366 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>` 367 has never been called, or ``CEC_MSG_FL_RAW`` was used from a process that 368 did not have the ``CAP_SYS_RAWIO`` capability. 369 370ENONET 371 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>` 372 was called, but the physical address is invalid so no logical address was claimed. 373 An exception is made in this case for transmits from initiator 0xf ('Unregistered') 374 to destination 0 ('TV'). In that case the transmit will proceed as usual. 375 376EBUSY 377 Another filehandle is in exclusive follower or initiator mode, or the filehandle 378 is in mode ``CEC_MODE_NO_INITIATOR``. This is also returned if the transmit 379 queue is full. 380 381EINVAL 382 The contents of struct :c:type:`cec_msg` is invalid. 383 384ERESTARTSYS 385 The wait for a successful transmit was interrupted (e.g. by Ctrl-C).