1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 3.. _CEC_TRANSMIT: 4.. _CEC_RECEIVE: 5 6*********************************** 7ioctls CEC_RECEIVE and CEC_TRANSMIT 8*********************************** 9 10Name 11==== 12 13CEC_RECEIVE, CEC_TRANSMIT - Receive or transmit a CEC message 14 15 16Synopsis 17======== 18 19.. c:function:: int ioctl( int fd, CEC_RECEIVE, struct cec_msg \*argp ) 20 :name: CEC_RECEIVE 21 22.. c:function:: int ioctl( int fd, CEC_TRANSMIT, struct cec_msg \*argp ) 23 :name: CEC_TRANSMIT 24 25Arguments 26========= 27 28``fd`` 29 File descriptor returned by :c:func:`open() <cec-open>`. 30 31``argp`` 32 Pointer to struct cec_msg. 33 34Description 35=========== 36 37To receive a CEC message the application has to fill in the 38``timeout`` field of struct :c:type:`cec_msg` and pass it to 39:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 40If the file descriptor is in non-blocking mode and there are no received 41messages pending, then it will return -1 and set errno to the ``EAGAIN`` 42error code. If the file descriptor is in blocking mode and ``timeout`` 43is non-zero and no message arrived within ``timeout`` milliseconds, then 44it will return -1 and set errno to the ``ETIMEDOUT`` error code. 45 46A received message can be: 47 481. a message received from another CEC device (the ``sequence`` field will 49 be 0). 502. the result of an earlier non-blocking transmit (the ``sequence`` field will 51 be non-zero). 52 53To send a CEC message the application has to fill in the struct 54:c:type:`cec_msg` and pass it to :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. 55The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is only available if 56``CEC_CAP_TRANSMIT`` is set. If there is no more room in the transmit 57queue, then it will return -1 and set errno to the ``EBUSY`` error code. 58The transmit queue has enough room for 18 messages (about 1 second worth 59of 2-byte messages). Note that the CEC kernel framework will also reply 60to core messages (see :ref:`cec-core-processing`), so it is not a good 61idea to fully fill up the transmit queue. 62 63If the file descriptor is in non-blocking mode then the transmit will 64return 0 and the result of the transmit will be available via 65:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` once the transmit has finished 66(including waiting for a reply, if requested). 67 68The ``sequence`` field is filled in for every transmit and this can be 69checked against the received messages to find the corresponding transmit 70result. 71 72Normally calling :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` when the physical 73address is invalid (due to e.g. a disconnect) will return ``ENONET``. 74 75However, the CEC specification allows sending messages from 'Unregistered' to 76'TV' when the physical address is invalid since some TVs pull the hotplug detect 77pin of the HDMI connector low when they go into standby, or when switching to 78another input. 79 80When the hotplug detect pin goes low the EDID disappears, and thus the 81physical address, but the cable is still connected and CEC still works. 82In order to detect/wake up the device it is allowed to send poll and 'Image/Text 83View On' messages from initiator 0xf ('Unregistered') to destination 0 ('TV'). 84 85.. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{13.0cm}| 86 87.. c:type:: cec_msg 88 89.. cssclass:: longtable 90 91.. flat-table:: struct cec_msg 92 :header-rows: 0 93 :stub-columns: 0 94 :widths: 1 1 16 95 96 * - __u64 97 - ``tx_ts`` 98 - Timestamp in ns of when the last byte of the message was transmitted. 99 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access 100 the same clock from userspace use :c:func:`clock_gettime`. 101 * - __u64 102 - ``rx_ts`` 103 - Timestamp in ns of when the last byte of the message was received. 104 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access 105 the same clock from userspace use :c:func:`clock_gettime`. 106 * - __u32 107 - ``len`` 108 - The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in 109 by the application. The driver will fill this in for 110 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be 111 filled in by the driver with the length of the reply message if ``reply`` was set. 112 * - __u32 113 - ``timeout`` 114 - The timeout in milliseconds. This is the time the device will wait 115 for a message to be received before timing out. If it is set to 0, 116 then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 117 If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, 118 then it will be replaced by 1000 if the ``reply`` is non-zero or 119 ignored if ``reply`` is 0. 120 * - __u32 121 - ``sequence`` 122 - A non-zero sequence number is automatically assigned by the CEC framework 123 for all transmitted messages. It is used by the CEC framework when it queues 124 the transmit result (when transmit was called in non-blocking mode). This 125 allows the application to associate the received message with the original 126 transmit. 127 * - __u32 128 - ``flags`` 129 - Flags. See :ref:`cec-msg-flags` for a list of available flags. 130 * - __u8 131 - ``tx_status`` 132 - The status bits of the transmitted message. See 133 :ref:`cec-tx-status` for the possible status values. It is 0 if 134 this message was received, not transmitted. 135 * - __u8 136 - ``msg[16]`` 137 - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the 138 application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 139 For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with 140 the payload of the reply message if ``timeout`` was set. 141 * - __u8 142 - ``reply`` 143 - Wait until this message is replied. If ``reply`` is 0 and the 144 ``timeout`` is 0, then don't wait for a reply but return after 145 transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 146 The case where ``reply`` is 0 (this is the opcode for the Feature Abort 147 message) and ``timeout`` is non-zero is specifically allowed to make it 148 possible to send a message and wait up to ``timeout`` milliseconds for a 149 Feature Abort reply. In this case ``rx_status`` will either be set 150 to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or 151 :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`. 152 153 If the transmitter message is ``CEC_MSG_INITIATE_ARC`` then the ``reply`` 154 values ``CEC_MSG_REPORT_ARC_INITIATED`` and ``CEC_MSG_REPORT_ARC_TERMINATED`` 155 are processed differently: either value will match both possible replies. 156 The reason is that the ``CEC_MSG_INITIATE_ARC`` message is the only CEC 157 message that has two possible replies other than Feature Abort. The 158 ``reply`` field will be updated with the actual reply so that it is 159 synchronized with the contents of the received message. 160 * - __u8 161 - ``rx_status`` 162 - The status bits of the received message. See 163 :ref:`cec-rx-status` for the possible status values. It is 0 if 164 this message was transmitted, not received, unless this is the 165 reply to a transmitted message. In that case both ``rx_status`` 166 and ``tx_status`` are set. 167 * - __u8 168 - ``tx_status`` 169 - The status bits of the transmitted message. See 170 :ref:`cec-tx-status` for the possible status values. It is 0 if 171 this message was received, not transmitted. 172 * - __u8 173 - ``tx_arb_lost_cnt`` 174 - A counter of the number of transmit attempts that resulted in the 175 Arbitration Lost error. This is only set if the hardware supports 176 this, otherwise it is always 0. This counter is only valid if the 177 :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set. 178 * - __u8 179 - ``tx_nack_cnt`` 180 - A counter of the number of transmit attempts that resulted in the 181 Not Acknowledged error. This is only set if the hardware supports 182 this, otherwise it is always 0. This counter is only valid if the 183 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set. 184 * - __u8 185 - ``tx_low_drive_cnt`` 186 - A counter of the number of transmit attempts that resulted in the 187 Arbitration Lost error. This is only set if the hardware supports 188 this, otherwise it is always 0. This counter is only valid if the 189 :ref:`CEC_TX_STATUS_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set. 190 * - __u8 191 - ``tx_error_cnt`` 192 - A counter of the number of transmit errors other than Arbitration 193 Lost or Not Acknowledged. This is only set if the hardware 194 supports this, otherwise it is always 0. This counter is only 195 valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set. 196 197 198.. tabularcolumns:: |p{6.2cm}|p{1.0cm}|p{10.3cm}| 199 200.. _cec-msg-flags: 201 202.. flat-table:: Flags for struct cec_msg 203 :header-rows: 0 204 :stub-columns: 0 205 :widths: 3 1 4 206 207 * .. _`CEC-MSG-FL-REPLY-TO-FOLLOWERS`: 208 209 - ``CEC_MSG_FL_REPLY_TO_FOLLOWERS`` 210 - 1 211 - If a CEC transmit expects a reply, then by default that reply is only sent to 212 the filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. If this 213 flag is set, then the reply is also sent to all followers, if any. If the 214 filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is also a 215 follower, then that filehandle will receive the reply twice: once as the 216 result of the :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, and once via 217 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 218 219 * .. _`CEC-MSG-FL-RAW`: 220 221 - ``CEC_MSG_FL_RAW`` 222 - 2 223 - Normally CEC messages are validated before transmitting them. If this 224 flag is set when :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is called, 225 then no validation takes place and the message is transmitted as-is. 226 This is useful when debugging CEC issues. 227 This flag is only allowed if the process has the ``CAP_SYS_RAWIO`` 228 capability. If that is not set, then the ``EPERM`` error code is 229 returned. 230 231 232.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}| 233 234.. _cec-tx-status: 235 236.. flat-table:: CEC Transmit Status 237 :header-rows: 0 238 :stub-columns: 0 239 :widths: 3 1 16 240 241 * .. _`CEC-TX-STATUS-OK`: 242 243 - ``CEC_TX_STATUS_OK`` 244 - 0x01 245 - The message was transmitted successfully. This is mutually 246 exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`. 247 Other bits can still be set if earlier attempts met with failure before 248 the transmit was eventually successful. 249 * .. _`CEC-TX-STATUS-ARB-LOST`: 250 251 - ``CEC_TX_STATUS_ARB_LOST`` 252 - 0x02 253 - CEC line arbitration was lost, i.e. another transmit started at the 254 same time with a higher priority. Optional status, not all hardware 255 can detect this error condition. 256 * .. _`CEC-TX-STATUS-NACK`: 257 258 - ``CEC_TX_STATUS_NACK`` 259 - 0x04 260 - Message was not acknowledged. Note that some hardware cannot tell apart 261 a 'Not Acknowledged' status from other error conditions, i.e. the result 262 of a transmit is just OK or FAIL. In that case this status will be 263 returned when the transmit failed. 264 * .. _`CEC-TX-STATUS-LOW-DRIVE`: 265 266 - ``CEC_TX_STATUS_LOW_DRIVE`` 267 - 0x08 268 - Low drive was detected on the CEC bus. This indicates that a 269 follower detected an error on the bus and requests a 270 retransmission. Optional status, not all hardware can detect this 271 error condition. 272 * .. _`CEC-TX-STATUS-ERROR`: 273 274 - ``CEC_TX_STATUS_ERROR`` 275 - 0x10 276 - Some error occurred. This is used for any errors that do not fit 277 ``CEC_TX_STATUS_ARB_LOST`` or ``CEC_TX_STATUS_LOW_DRIVE``, either because 278 the hardware could not tell which error occurred, or because the hardware 279 tested for other conditions besides those two. Optional status. 280 * .. _`CEC-TX-STATUS-MAX-RETRIES`: 281 282 - ``CEC_TX_STATUS_MAX_RETRIES`` 283 - 0x20 284 - The transmit failed after one or more retries. This status bit is 285 mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`. 286 Other bits can still be set to explain which failures were seen. 287 * .. _`CEC-TX-STATUS-ABORTED`: 288 289 - ``CEC_TX_STATUS_ABORTED`` 290 - 0x40 291 - The transmit was aborted due to an HDMI disconnect, or the adapter 292 was unconfigured, or a transmit was interrupted, or the driver 293 returned an error when attempting to start a transmit. 294 * .. _`CEC-TX-STATUS-TIMEOUT`: 295 296 - ``CEC_TX_STATUS_TIMEOUT`` 297 - 0x80 298 - The transmit timed out. This should not normally happen and this 299 indicates a driver problem. 300 301 302.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}| 303 304.. _cec-rx-status: 305 306.. flat-table:: CEC Receive Status 307 :header-rows: 0 308 :stub-columns: 0 309 :widths: 3 1 16 310 311 * .. _`CEC-RX-STATUS-OK`: 312 313 - ``CEC_RX_STATUS_OK`` 314 - 0x01 315 - The message was received successfully. 316 * .. _`CEC-RX-STATUS-TIMEOUT`: 317 318 - ``CEC_RX_STATUS_TIMEOUT`` 319 - 0x02 320 - The reply to an earlier transmitted message timed out. 321 * .. _`CEC-RX-STATUS-FEATURE-ABORT`: 322 323 - ``CEC_RX_STATUS_FEATURE_ABORT`` 324 - 0x04 325 - The message was received successfully but the reply was 326 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message 327 was the reply to an earlier transmitted message. 328 * .. _`CEC-RX-STATUS-ABORTED`: 329 330 - ``CEC_RX_STATUS_ABORTED`` 331 - 0x08 332 - The wait for a reply to an earlier transmitted message was aborted 333 because the HDMI cable was disconnected, the adapter was unconfigured 334 or the :ref:`CEC_TRANSMIT <CEC_RECEIVE>` that waited for a 335 reply was interrupted. 336 337 338 339Return Value 340============ 341 342On success 0 is returned, on error -1 and the ``errno`` variable is set 343appropriately. The generic error codes are described at the 344:ref:`Generic Error Codes <gen-errors>` chapter. 345 346The :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` can return the following 347error codes: 348 349EAGAIN 350 No messages are in the receive queue, and the filehandle is in non-blocking mode. 351 352ETIMEDOUT 353 The ``timeout`` was reached while waiting for a message. 354 355ERESTARTSYS 356 The wait for a message was interrupted (e.g. by Ctrl-C). 357 358The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` can return the following 359error codes: 360 361ENOTTY 362 The ``CEC_CAP_TRANSMIT`` capability wasn't set, so this ioctl is not supported. 363 364EPERM 365 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>` 366 has never been called, or ``CEC_MSG_FL_RAW`` was used from a process that 367 did not have the ``CAP_SYS_RAWIO`` capability. 368 369ENONET 370 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>` 371 was called, but the physical address is invalid so no logical address was claimed. 372 An exception is made in this case for transmits from initiator 0xf ('Unregistered') 373 to destination 0 ('TV'). In that case the transmit will proceed as usual. 374 375EBUSY 376 Another filehandle is in exclusive follower or initiator mode, or the filehandle 377 is in mode ``CEC_MODE_NO_INITIATOR``. This is also returned if the transmit 378 queue is full. 379 380EINVAL 381 The contents of struct :c:type:`cec_msg` is invalid. 382 383ERESTARTSYS 384 The wait for a successful transmit was interrupted (e.g. by Ctrl-C). 385