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.
39 This documents the proposed CEC API. This API is not yet finalized
40 and is currently only available as a staging kernel module.
42 To receive a CEC message the application has to fill in the
43 ``timeout`` field of struct :c:type:`cec_msg` and pass it to
44 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
45 If the file descriptor is in non-blocking mode and there are no received
46 messages pending, then it will return -1 and set errno to the ``EAGAIN``
47 error code. If the file descriptor is in blocking mode and ``timeout``
48 is non-zero and no message arrived within ``timeout`` milliseconds, then
49 it will return -1 and set errno to the ``ETIMEDOUT`` error code.
51 A received message can be:
53 1. a message received from another CEC device (the ``sequence`` field will
55 2. the result of an earlier non-blocking transmit (the ``sequence`` field will
58 To 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>`.
60 The :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
62 queue, then it will return -1 and set errno to the ``EBUSY`` error code.
63 The transmit queue has enough room for 18 messages (about 1 second worth
64 of 2-byte messages). Note that the CEC kernel framework will also reply
65 to core messages (see :ref:cec-core-processing), so it is not a good
66 idea to fully fill up the transmit queue.
68 If the file descriptor is in non-blocking mode then the transmit will
69 return 0 and the result of the transmit will be available via
70 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` once the transmit has finished
71 (including waiting for a reply, if requested).
73 The ``sequence`` field is filled in for every transmit and this can be
74 checked against the received messages to find the corresponding transmit
78 .. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{13.0cm}|
82 .. cssclass:: longtable
84 .. flat-table:: struct cec_msg
96 - Timestamp in ns of when the last byte of the message was transmitted.
97 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
98 the same clock from userspace use :c:func:`clock_gettime`.
106 - Timestamp in ns of when the last byte of the message was received.
107 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
108 the same clock from userspace use :c:func:`clock_gettime`.
116 - The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in
117 by the application. The driver will fill this in for
118 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be
119 filled in by the driver with the length of the reply message if ``reply`` was set.
127 - The timeout in milliseconds. This is the time the device will wait
128 for a message to be received before timing out. If it is set to 0,
129 then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
130 If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`,
131 then it will be replaced by 1000 if the ``reply`` is non-zero or
132 ignored if ``reply`` is 0.
140 - A non-zero sequence number is automatically assigned by the CEC framework
141 for all transmitted messages. It is used by the CEC framework when it queues
142 the transmit result (when transmit was called in non-blocking mode). This
143 allows the application to associate the received message with the original
152 - Flags. No flags are defined yet, so set this to 0.
160 - The status bits of the transmitted message. See
161 :ref:`cec-tx-status` for the possible status values. It is 0 if
162 this messages was received, not transmitted.
170 - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the
171 application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
172 For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with
173 the payload of the reply message if ``timeout`` was set.
181 - Wait until this message is replied. If ``reply`` is 0 and the
182 ``timeout`` is 0, then don't wait for a reply but return after
183 transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
184 The case where ``reply`` is 0 (this is the opcode for the Feature Abort
185 message) and ``timeout`` is non-zero is specifically allowed to make it
186 possible to send a message and wait up to ``timeout`` milliseconds for a
187 Feature Abort reply. In this case ``rx_status`` will either be set
188 to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or
189 :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`.
197 - The status bits of the received message. See
198 :ref:`cec-rx-status` for the possible status values. It is 0 if
199 this message was transmitted, not received, unless this is the
200 reply to a transmitted message. In that case both ``rx_status``
201 and ``tx_status`` are set.
209 - The status bits of the transmitted message. See
210 :ref:`cec-tx-status` for the possible status values. It is 0 if
211 this messages was received, not transmitted.
217 - ``tx_arb_lost_cnt``
219 - A counter of the number of transmit attempts that resulted in the
220 Arbitration Lost error. This is only set if the hardware supports
221 this, otherwise it is always 0. This counter is only valid if the
222 :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set.
230 - A counter of the number of transmit attempts that resulted in the
231 Not Acknowledged error. This is only set if the hardware supports
232 this, otherwise it is always 0. This counter is only valid if the
233 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set.
239 - ``tx_low_drive_cnt``
241 - A counter of the number of transmit attempts that resulted in the
242 Arbitration Lost error. This is only set if the hardware supports
243 this, otherwise it is always 0. This counter is only valid if the
244 :ref:`CEC_TX_STATUS_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set.
252 - A counter of the number of transmit errors other than Arbitration
253 Lost or Not Acknowledged. This is only set if the hardware
254 supports this, otherwise it is always 0. This counter is only
255 valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set.
258 .. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
262 .. flat-table:: CEC Transmit Status
268 - .. _`CEC-TX-STATUS-OK`:
270 - ``CEC_TX_STATUS_OK``
274 - The message was transmitted successfully. This is mutually
275 exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`. Other bits can still
276 be set if earlier attempts met with failure before the transmit
277 was eventually successful.
279 - .. _`CEC-TX-STATUS-ARB-LOST`:
281 - ``CEC_TX_STATUS_ARB_LOST``
285 - CEC line arbitration was lost.
287 - .. _`CEC-TX-STATUS-NACK`:
289 - ``CEC_TX_STATUS_NACK``
293 - Message was not acknowledged.
295 - .. _`CEC-TX-STATUS-LOW-DRIVE`:
297 - ``CEC_TX_STATUS_LOW_DRIVE``
301 - Low drive was detected on the CEC bus. This indicates that a
302 follower detected an error on the bus and requests a
305 - .. _`CEC-TX-STATUS-ERROR`:
307 - ``CEC_TX_STATUS_ERROR``
311 - Some error occurred. This is used for any errors that do not fit
312 the previous two, either because the hardware could not tell which
313 error occurred, or because the hardware tested for other
314 conditions besides those two.
316 - .. _`CEC-TX-STATUS-MAX-RETRIES`:
318 - ``CEC_TX_STATUS_MAX_RETRIES``
322 - The transmit failed after one or more retries. This status bit is
323 mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`. Other bits can still
324 be set to explain which failures were seen.
327 .. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
331 .. flat-table:: CEC Receive Status
337 - .. _`CEC-RX-STATUS-OK`:
339 - ``CEC_RX_STATUS_OK``
343 - The message was received successfully.
345 - .. _`CEC-RX-STATUS-TIMEOUT`:
347 - ``CEC_RX_STATUS_TIMEOUT``
351 - The reply to an earlier transmitted message timed out.
353 - .. _`CEC-RX-STATUS-FEATURE-ABORT`:
355 - ``CEC_RX_STATUS_FEATURE_ABORT``
359 - The message was received successfully but the reply was
360 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message
361 was the reply to an earlier transmitted message.
368 On success 0 is returned, on error -1 and the ``errno`` variable is set
369 appropriately. The generic error codes are described at the
370 :ref:`Generic Error Codes <gen-errors>` chapter.