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 .. cpp:function:: int ioctl( int fd, int request, struct cec_msg *argp )
25 File descriptor returned by :ref:`open() <cec-func-open>`.
28 CEC_RECEIVE, CEC_TRANSMIT
38 This documents the proposed CEC API. This API is not yet finalized
39 and is currently only available as a staging kernel module.
41 To receive a CEC message the application has to fill in the
42 ``timeout`` field of :c:type:`struct cec_msg` and pass it to :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
43 If the file descriptor is in non-blocking mode and there are no received
44 messages pending, then it will return -1 and set errno to the ``EAGAIN``
45 error code. If the file descriptor is in blocking mode and ``timeout``
46 is non-zero and no message arrived within ``timeout`` milliseconds, then
47 it will return -1 and set errno to the ``ETIMEDOUT`` error code.
49 A received message can be:
51 1. a message received from another CEC device (the ``sequence`` field will
53 2. the result of an earlier non-blocking transmit (the ``sequence`` field will
56 To send a CEC message the application has to fill in the
57 :c:type:`struct cec_msg` and pass it to
58 :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is only available if
59 ``CEC_CAP_TRANSMIT`` is set. If there is no more room in the transmit
60 queue, then it will return -1 and set errno to the ``EBUSY`` error code.
61 The transmit queue has enough room for 18 messages (about 1 second worth
62 of 2-byte messages). Note that the CEC kernel framework will also reply
63 to core messages (see :ref:cec-core-processing), so it is not a good
64 idea to fully fill up the transmit queue.
66 If the file descriptor is in non-blocking mode then the transmit will
67 return 0 and the result of the transmit will be available via
68 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` once the transmit has finished
69 (including waiting for a reply, if requested).
71 The ``sequence`` field is filled in for every transmit and this can be
72 checked against the received messages to find the corresponding transmit
78 .. flat-table:: struct cec_msg
90 - Timestamp in ns of when the last byte of the message was transmitted.
91 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
92 the same clock from userspace use :c:func:`clock_gettime(2)`.
100 - Timestamp in ns of when the last byte of the message was received.
101 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
102 the same clock from userspace use :c:func:`clock_gettime(2)`.
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.
121 - The timeout in milliseconds. This is the time the device will wait
122 for a message to be received before timing out. If it is set to 0,
123 then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
124 If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`,
125 then it will be replaced by 1000 if the ``reply`` is non-zero or
126 ignored if ``reply`` is 0.
134 - A non-zero sequence number is automatically assigned by the CEC framework
135 for all transmitted messages. It is used by the CEC framework when it queues
136 the transmit result (when transmit was called in non-blocking mode). This
137 allows the application to associate the received message with the original
146 - Flags. No flags are defined yet, so set this to 0.
154 - The status bits of the transmitted message. See
155 :ref:`cec-tx-status` for the possible status values. It is 0 if
156 this messages was received, not transmitted.
164 - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the
165 application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
166 For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with
167 the payload of the reply message if ``timeout`` was set.
175 - Wait until this message is replied. If ``reply`` is 0 and the
176 ``timeout`` is 0, then don't wait for a reply but return after
177 transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
178 The case where ``reply`` is 0 (this is the opcode for the Feature Abort
179 message) and ``timeout`` is non-zero is specifically allowed to make it
180 possible to send a message and wait up to ``timeout`` milliseconds for a
181 Feature Abort reply. In this case ``rx_status`` will either be set
182 to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or
183 :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`.
191 - The status bits of the received message. See
192 :ref:`cec-rx-status` for the possible status values. It is 0 if
193 this message was transmitted, not received, unless this is the
194 reply to a transmitted message. In that case both ``rx_status``
195 and ``tx_status`` are set.
203 - The status bits of the transmitted message. See
204 :ref:`cec-tx-status` for the possible status values. It is 0 if
205 this messages was received, not transmitted.
211 - ``tx_arb_lost_cnt``
213 - A counter of the number of transmit attempts that resulted in the
214 Arbitration Lost error. This is only set if the hardware supports
215 this, otherwise it is always 0. This counter is only valid if the
216 :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set.
224 - A counter of the number of transmit attempts that resulted in the
225 Not Acknowledged error. This is only set if the hardware supports
226 this, otherwise it is always 0. This counter is only valid if the
227 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set.
233 - ``tx_low_drive_cnt``
235 - A counter of the number of transmit attempts that resulted in the
236 Arbitration Lost error. This is only set if the hardware supports
237 this, otherwise it is always 0. This counter is only valid if the
238 :ref:`CEC_TX_STATUS_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set.
246 - A counter of the number of transmit errors other than Arbitration
247 Lost or Not Acknowledged. This is only set if the hardware
248 supports this, otherwise it is always 0. This counter is only
249 valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set.
255 .. flat-table:: CEC Transmit Status
261 - .. _`CEC-TX-STATUS-OK`:
263 - ``CEC_TX_STATUS_OK``
267 - The message was transmitted successfully. This is mutually
268 exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`. Other bits can still
269 be set if earlier attempts met with failure before the transmit
270 was eventually successful.
272 - .. _`CEC-TX-STATUS-ARB-LOST`:
274 - ``CEC_TX_STATUS_ARB_LOST``
278 - CEC line arbitration was lost.
280 - .. _`CEC-TX-STATUS-NACK`:
282 - ``CEC_TX_STATUS_NACK``
286 - Message was not acknowledged.
288 - .. _`CEC-TX-STATUS-LOW-DRIVE`:
290 - ``CEC_TX_STATUS_LOW_DRIVE``
294 - Low drive was detected on the CEC bus. This indicates that a
295 follower detected an error on the bus and requests a
298 - .. _`CEC-TX-STATUS-ERROR`:
300 - ``CEC_TX_STATUS_ERROR``
304 - Some error occurred. This is used for any errors that do not fit
305 the previous two, either because the hardware could not tell which
306 error occurred, or because the hardware tested for other
307 conditions besides those two.
309 - .. _`CEC-TX-STATUS-MAX-RETRIES`:
311 - ``CEC_TX_STATUS_MAX_RETRIES``
315 - The transmit failed after one or more retries. This status bit is
316 mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`. Other bits can still
317 be set to explain which failures were seen.
323 .. flat-table:: CEC Receive Status
329 - .. _`CEC-RX-STATUS-OK`:
331 - ``CEC_RX_STATUS_OK``
335 - The message was received successfully.
337 - .. _`CEC-RX-STATUS-TIMEOUT`:
339 - ``CEC_RX_STATUS_TIMEOUT``
343 - The reply to an earlier transmitted message timed out.
345 - .. _`CEC-RX-STATUS-FEATURE-ABORT`:
347 - ``CEC_RX_STATUS_FEATURE_ABORT``
351 - The message was received successfully but the reply was
352 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message
353 was the reply to an earlier transmitted message.
360 On success 0 is returned, on error -1 and the ``errno`` variable is set
361 appropriately. The generic error codes are described at the
362 :ref:`Generic Error Codes <gen-errors>` chapter.