1 .. -*- coding: utf-8; mode: rst -*-
6 ***********************************
7 ioctls CEC_RECEIVE and CEC_TRANSMIT
8 ***********************************
13 CEC_RECEIVE, CEC_TRANSMIT - Receive or transmit a CEC message
19 .. c:function:: int ioctl( int fd, CEC_RECEIVE, struct cec_msg \*argp )
22 .. c:function:: int ioctl( int fd, CEC_TRANSMIT, struct cec_msg \*argp )
29 File descriptor returned by :c:func:`open() <cec-open>`.
32 Pointer to struct cec_msg.
37 To 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>`.
40 If the file descriptor is in non-blocking mode and there are no received
41 messages pending, then it will return -1 and set errno to the ``EAGAIN``
42 error code. If the file descriptor is in blocking mode and ``timeout``
43 is non-zero and no message arrived within ``timeout`` milliseconds, then
44 it will return -1 and set errno to the ``ETIMEDOUT`` error code.
46 A received message can be:
48 1. a message received from another CEC device (the ``sequence`` field will
50 2. the result of an earlier non-blocking transmit (the ``sequence`` field will
53 To 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>`.
55 The :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
57 queue, then it will return -1 and set errno to the ``EBUSY`` error code.
58 The transmit queue has enough room for 18 messages (about 1 second worth
59 of 2-byte messages). Note that the CEC kernel framework will also reply
60 to core messages (see :ref:`cec-core-processing`), so it is not a good
61 idea to fully fill up the transmit queue.
63 If the file descriptor is in non-blocking mode then the transmit will
64 return 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).
68 The ``sequence`` field is filled in for every transmit and this can be
69 checked against the received messages to find the corresponding transmit
72 Normally calling :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` when the physical
73 address is invalid (due to e.g. a disconnect) will return ``ENONET``.
75 However, the CEC specification allows sending messages from 'Unregistered' to
76 'TV' when the physical address is invalid since some TVs pull the hotplug detect
77 pin of the HDMI connector low when they go into standby, or when switching to
80 When the hotplug detect pin goes low the EDID disappears, and thus the
81 physical address, but the cable is still connected and CEC still works.
82 In order to detect/wake up the device it is allowed to send poll and 'Image/Text
83 View On' messages from initiator 0xf ('Unregistered') to destination 0 ('TV').
85 .. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{13.0cm}|
89 .. cssclass:: longtable
91 .. flat-table:: struct cec_msg
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`.
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`.
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.
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.
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
129 - Flags. See :ref:`cec-msg-flags` for a list of available flags.
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.
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.
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>`.
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.
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.
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.
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.
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.
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.
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.
198 .. tabularcolumns:: |p{6.2cm}|p{1.0cm}|p{10.3cm}|
202 .. flat-table:: Flags for struct cec_msg
207 * .. _`CEC-MSG-FL-REPLY-TO-FOLLOWERS`:
209 - ``CEC_MSG_FL_REPLY_TO_FOLLOWERS``
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>`.
220 .. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
224 .. flat-table:: CEC Transmit Status
229 * .. _`CEC-TX-STATUS-OK`:
231 - ``CEC_TX_STATUS_OK``
233 - The message was transmitted successfully. This is mutually
234 exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`.
235 Other bits can still be set if earlier attempts met with failure before
236 the transmit was eventually successful.
237 * .. _`CEC-TX-STATUS-ARB-LOST`:
239 - ``CEC_TX_STATUS_ARB_LOST``
241 - CEC line arbitration was lost, i.e. another transmit started at the
242 same time with a higher priority. Optional status, not all hardware
243 can detect this error condition.
244 * .. _`CEC-TX-STATUS-NACK`:
246 - ``CEC_TX_STATUS_NACK``
248 - Message was not acknowledged. Note that some hardware cannot tell apart
249 a 'Not Acknowledged' status from other error conditions, i.e. the result
250 of a transmit is just OK or FAIL. In that case this status will be
251 returned when the transmit failed.
252 * .. _`CEC-TX-STATUS-LOW-DRIVE`:
254 - ``CEC_TX_STATUS_LOW_DRIVE``
256 - Low drive was detected on the CEC bus. This indicates that a
257 follower detected an error on the bus and requests a
258 retransmission. Optional status, not all hardware can detect this
260 * .. _`CEC-TX-STATUS-ERROR`:
262 - ``CEC_TX_STATUS_ERROR``
264 - Some error occurred. This is used for any errors that do not fit
265 ``CEC_TX_STATUS_ARB_LOST`` or ``CEC_TX_STATUS_LOW_DRIVE``, either because
266 the hardware could not tell which error occurred, or because the hardware
267 tested for other conditions besides those two. Optional status.
268 * .. _`CEC-TX-STATUS-MAX-RETRIES`:
270 - ``CEC_TX_STATUS_MAX_RETRIES``
272 - The transmit failed after one or more retries. This status bit is
273 mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`.
274 Other bits can still be set to explain which failures were seen.
275 * .. _`CEC-TX-STATUS-ABORTED`:
277 - ``CEC_TX_STATUS_ABORTED``
279 - The transmit was aborted due to an HDMI disconnect, or the adapter
280 was unconfigured, or a transmit was interrupted, or the driver
281 returned an error when attempting to start a transmit.
282 * .. _`CEC-TX-STATUS-TIMEOUT`:
284 - ``CEC_TX_STATUS_TIMEOUT``
286 - The transmit timed out. This should not normally happen and this
287 indicates a driver problem.
290 .. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
294 .. flat-table:: CEC Receive Status
299 * .. _`CEC-RX-STATUS-OK`:
301 - ``CEC_RX_STATUS_OK``
303 - The message was received successfully.
304 * .. _`CEC-RX-STATUS-TIMEOUT`:
306 - ``CEC_RX_STATUS_TIMEOUT``
308 - The reply to an earlier transmitted message timed out.
309 * .. _`CEC-RX-STATUS-FEATURE-ABORT`:
311 - ``CEC_RX_STATUS_FEATURE_ABORT``
313 - The message was received successfully but the reply was
314 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message
315 was the reply to an earlier transmitted message.
316 * .. _`CEC-RX-STATUS-ABORTED`:
318 - ``CEC_RX_STATUS_ABORTED``
320 - The wait for a reply to an earlier transmitted message was aborted
321 because the HDMI cable was disconnected, the adapter was unconfigured
322 or the :ref:`CEC_TRANSMIT <CEC_RECEIVE>` that waited for a
323 reply was interrupted.
330 On success 0 is returned, on error -1 and the ``errno`` variable is set
331 appropriately. The generic error codes are described at the
332 :ref:`Generic Error Codes <gen-errors>` chapter.
334 The :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` can return the following
338 No messages are in the receive queue, and the filehandle is in non-blocking mode.
341 The ``timeout`` was reached while waiting for a message.
344 The wait for a message was interrupted (e.g. by Ctrl-C).
346 The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` can return the following
350 The ``CEC_CAP_TRANSMIT`` capability wasn't set, so this ioctl is not supported.
353 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>`
354 has never been called.
357 The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>`
358 was called, but the physical address is invalid so no logical address was claimed.
359 An exception is made in this case for transmits from initiator 0xf ('Unregistered')
360 to destination 0 ('TV'). In that case the transmit will proceed as usual.
363 Another filehandle is in exclusive follower or initiator mode, or the filehandle
364 is in mode ``CEC_MODE_NO_INITIATOR``. This is also returned if the transmit
368 The contents of struct :c:type:`cec_msg` is invalid.
371 The wait for a successful transmit was interrupted (e.g. by Ctrl-C).