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). 522. the result of an earlier non-blocking transmit (the ``sequence`` field will 53 be non-zero). 54 55To send a CEC message the application has to fill in the struct 56:c:type:`cec_msg` and pass it to :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. 57The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is only available if 58``CEC_CAP_TRANSMIT`` is set. If there is no more room in the transmit 59queue, then it will return -1 and set errno to the ``EBUSY`` error code. 60The transmit queue has enough room for 18 messages (about 1 second worth 61of 2-byte messages). Note that the CEC kernel framework will also reply 62to core messages (see :ref:`cec-core-processing`), so it is not a good 63idea to fully fill up the transmit queue. 64 65If the file descriptor is in non-blocking mode then the transmit will 66return 0 and the result of the transmit will be available via 67:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` once the transmit has finished 68(including waiting for a reply, if requested). 69 70The ``sequence`` field is filled in for every transmit and this can be 71checked against the received messages to find the corresponding transmit 72result. 73 74Normally calling :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` when the physical 75address is invalid (due to e.g. a disconnect) will return ``ENONET``. 76 77However, the CEC specification allows sending messages from 'Unregistered' to 78'TV' when the physical address is invalid since some TVs pull the hotplug detect 79pin of the HDMI connector low when they go into standby, or when switching to 80another input. 81 82When the hotplug detect pin goes low the EDID disappears, and thus the 83physical address, but the cable is still connected and CEC still works. 84In order to detect/wake up the device it is allowed to send poll and 'Image/Text 85View On' messages from initiator 0xf ('Unregistered') to destination 0 ('TV'). 86 87.. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{12.8cm}| 88 89.. c:type:: cec_msg 90 91.. cssclass:: longtable 92 93.. flat-table:: struct cec_msg 94 :header-rows: 0 95 :stub-columns: 0 96 :widths: 1 1 16 97 98 * - __u64 99 - ``tx_ts`` 100 - Timestamp in ns of when the last byte of the message was transmitted. 101 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access 102 the same clock from userspace use :c:func:`clock_gettime`. 103 * - __u64 104 - ``rx_ts`` 105 - Timestamp in ns of when the last byte of the message was received. 106 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access 107 the same clock from userspace use :c:func:`clock_gettime`. 108 * - __u32 109 - ``len`` 110 - The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in 111 by the application. The driver will fill this in for 112 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be 113 filled in by the driver with the length of the reply message if ``reply`` was set. 114 * - __u32 115 - ``timeout`` 116 - The timeout in milliseconds. This is the time the device will wait 117 for a message to be received before timing out. If it is set to 0, 118 then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 119 If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, 120 then it will be replaced by 1000 if the ``reply`` is non-zero or 121 ignored if ``reply`` is 0. 122 * - __u32 123 - ``sequence`` 124 - A non-zero sequence number is automatically assigned by the CEC framework 125 for all transmitted messages. It is used by the CEC framework when it queues 126 the transmit result (when transmit was called in non-blocking mode). This 127 allows the application to associate the received message with the original 128 transmit. 129 * - __u32 130 - ``flags`` 131 - Flags. See :ref:`cec-msg-flags` for a list of available flags. 132 * - __u8 133 - ``tx_status`` 134 - The status bits of the transmitted message. See 135 :ref:`cec-tx-status` for the possible status values. It is 0 if 136 this message was received, not transmitted. 137 * - __u8 138 - ``msg[16]`` 139 - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the 140 application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 141 For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with 142 the payload of the reply message if ``timeout`` was set. 143 * - __u8 144 - ``reply`` 145 - Wait until this message is replied. If ``reply`` is 0 and the 146 ``timeout`` is 0, then don't wait for a reply but return after 147 transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 148 The case where ``reply`` is 0 (this is the opcode for the Feature Abort 149 message) and ``timeout`` is non-zero is specifically allowed to make it 150 possible to send a message and wait up to ``timeout`` milliseconds for a 151 Feature Abort reply. In this case ``rx_status`` will either be set 152 to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or 153 :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`. 154 155 If the transmitter message is ``CEC_MSG_INITIATE_ARC`` then the ``reply`` 156 values ``CEC_MSG_REPORT_ARC_INITIATED`` and ``CEC_MSG_REPORT_ARC_TERMINATED`` 157 are processed differently: either value will match both possible replies. 158 The reason is that the ``CEC_MSG_INITIATE_ARC`` message is the only CEC 159 message that has two possible replies other than Feature Abort. The 160 ``reply`` field will be updated with the actual reply so that it is 161 synchronized with the contents of the received message. 162 * - __u8 163 - ``rx_status`` 164 - The status bits of the received message. See 165 :ref:`cec-rx-status` for the possible status values. It is 0 if 166 this message was transmitted, not received, unless this is the 167 reply to a transmitted message. In that case both ``rx_status`` 168 and ``tx_status`` are set. 169 * - __u8 170 - ``tx_status`` 171 - The status bits of the transmitted message. See 172 :ref:`cec-tx-status` for the possible status values. It is 0 if 173 this message was received, not transmitted. 174 * - __u8 175 - ``tx_arb_lost_cnt`` 176 - A counter of the number of transmit attempts that resulted in the 177 Arbitration Lost error. This is only set if the hardware supports 178 this, otherwise it is always 0. This counter is only valid if the 179 :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set. 180 * - __u8 181 - ``tx_nack_cnt`` 182 - A counter of the number of transmit attempts that resulted in the 183 Not Acknowledged error. This is only set if the hardware supports 184 this, otherwise it is always 0. This counter is only valid if the 185 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set. 186 * - __u8 187 - ``tx_low_drive_cnt`` 188 - A counter of the number of transmit attempts that resulted in the 189 Arbitration Lost error. This is only set if the hardware supports 190 this, otherwise it is always 0. This counter is only valid if the 191 :ref:`CEC_TX_STATUS_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set. 192 * - __u8 193 - ``tx_error_cnt`` 194 - A counter of the number of transmit errors other than Arbitration 195 Lost or Not Acknowledged. This is only set if the hardware 196 supports this, otherwise it is always 0. This counter is only 197 valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set. 198 199.. tabularcolumns:: |p{6.2cm}|p{1.0cm}|p{10.1cm}| 200 201.. _cec-msg-flags: 202 203.. flat-table:: Flags for struct cec_msg 204 :header-rows: 0 205 :stub-columns: 0 206 :widths: 3 1 4 207 208 * .. _`CEC-MSG-FL-REPLY-TO-FOLLOWERS`: 209 210 - ``CEC_MSG_FL_REPLY_TO_FOLLOWERS`` 211 - 1 212 - If a CEC transmit expects a reply, then by default that reply is only sent to 213 the filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. If this 214 flag is set, then the reply is also sent to all followers, if any. If the 215 filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is also a 216 follower, then that filehandle will receive the reply twice: once as the 217 result of the :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, and once via 218 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. 219 220 * .. _`CEC-MSG-FL-RAW`: 221 222 - ``CEC_MSG_FL_RAW`` 223 - 2 224 - Normally CEC messages are validated before transmitting them. If this 225 flag is set when :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is called, 226 then no validation takes place and the message is transmitted as-is. 227 This is useful when debugging CEC issues. 228 This flag is only allowed if the process has the ``CAP_SYS_RAWIO`` 229 capability. If that is not set, then the ``EPERM`` error code is 230 returned. 231 232.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{10.8cm}| 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.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{10.8cm}| 302 303.. _cec-rx-status: 304 305.. flat-table:: CEC Receive Status 306 :header-rows: 0 307 :stub-columns: 0 308 :widths: 3 1 16 309 310 * .. _`CEC-RX-STATUS-OK`: 311 312 - ``CEC_RX_STATUS_OK`` 313 - 0x01 314 - The message was received successfully. 315 * .. _`CEC-RX-STATUS-TIMEOUT`: 316 317 - ``CEC_RX_STATUS_TIMEOUT`` 318 - 0x02 319 - The reply to an earlier transmitted message timed out. 320 * .. _`CEC-RX-STATUS-FEATURE-ABORT`: 321 322 - ``CEC_RX_STATUS_FEATURE_ABORT`` 323 - 0x04 324 - The message was received successfully but the reply was 325 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message 326 was the reply to an earlier transmitted message. 327 * .. _`CEC-RX-STATUS-ABORTED`: 328 329 - ``CEC_RX_STATUS_ABORTED`` 330 - 0x08 331 - The wait for a reply to an earlier transmitted message was aborted 332 because the HDMI cable was disconnected, the adapter was unconfigured 333 or the :ref:`CEC_TRANSMIT <CEC_RECEIVE>` that waited for a 334 reply was interrupted. 335 336 337Return Value 338============ 339 340On success 0 is returned, on error -1 and the ``errno`` variable is set 341appropriately. The generic error codes are described at the 342:ref:`Generic Error Codes <gen-errors>` chapter. 343 344The :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` can return the following 345error codes: 346 347EAGAIN 348 No messages are in the receive queue, and the filehandle is in non-blocking mode. 349 350ETIMEDOUT 351 The ``timeout`` was reached while waiting for a message. 352 353ERESTARTSYS 354 The wait for a message was interrupted (e.g. by Ctrl-C). 355 356The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` can return the following 357error codes: 358 359ENOTTY 360 The ``CEC_CAP_TRANSMIT`` capability wasn't set, so this ioctl is not supported. 361 362EPERM 363 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>` 364 has never been called, or ``CEC_MSG_FL_RAW`` was used from a process that 365 did not have the ``CAP_SYS_RAWIO`` capability. 366 367ENONET 368 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>` 369 was called, but the physical address is invalid so no logical address was claimed. 370 An exception is made in this case for transmits from initiator 0xf ('Unregistered') 371 to destination 0 ('TV'). In that case the transmit will proceed as usual. 372 373EBUSY 374 Another filehandle is in exclusive follower or initiator mode, or the filehandle 375 is in mode ``CEC_MODE_NO_INITIATOR``. This is also returned if the transmit 376 queue is full. 377 378EINVAL 379 The contents of struct :c:type:`cec_msg` is invalid. 380 381ERESTARTSYS 382 The wait for a successful transmit was interrupted (e.g. by Ctrl-C). 383