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 .. tabularcolumns:: |p{1.0cm}|p{1.0cm}|p{15.5cm}|
80 .. flat-table:: struct cec_msg
92 - Timestamp in ns of when the last byte of the message was transmitted.
93 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
94 the same clock from userspace use :c:func:`clock_gettime(2)`.
102 - Timestamp in ns of when the last byte of the message was received.
103 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
104 the same clock from userspace use :c:func:`clock_gettime(2)`.
112 - The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in
113 by the application. The driver will fill this in for
114 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be
115 filled in by the driver with the length of the reply message if ``reply`` was set.
123 - The timeout in milliseconds. This is the time the device will wait
124 for a message to be received before timing out. If it is set to 0,
125 then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
126 If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`,
127 then it will be replaced by 1000 if the ``reply`` is non-zero or
128 ignored if ``reply`` is 0.
136 - A non-zero sequence number is automatically assigned by the CEC framework
137 for all transmitted messages. It is used by the CEC framework when it queues
138 the transmit result (when transmit was called in non-blocking mode). This
139 allows the application to associate the received message with the original
148 - Flags. No flags are defined yet, so set this to 0.
156 - The status bits of the transmitted message. See
157 :ref:`cec-tx-status` for the possible status values. It is 0 if
158 this messages was received, not transmitted.
166 - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the
167 application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
168 For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with
169 the payload of the reply message if ``timeout`` was set.
177 - Wait until this message is replied. If ``reply`` is 0 and the
178 ``timeout`` is 0, then don't wait for a reply but return after
179 transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
180 The case where ``reply`` is 0 (this is the opcode for the Feature Abort
181 message) and ``timeout`` is non-zero is specifically allowed to make it
182 possible to send a message and wait up to ``timeout`` milliseconds for a
183 Feature Abort reply. In this case ``rx_status`` will either be set
184 to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or
185 :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`.
193 - The status bits of the received message. See
194 :ref:`cec-rx-status` for the possible status values. It is 0 if
195 this message was transmitted, not received, unless this is the
196 reply to a transmitted message. In that case both ``rx_status``
197 and ``tx_status`` are set.
205 - The status bits of the transmitted message. See
206 :ref:`cec-tx-status` for the possible status values. It is 0 if
207 this messages was received, not transmitted.
213 - ``tx_arb_lost_cnt``
215 - A counter of the number of transmit attempts that resulted in the
216 Arbitration Lost error. This is only set if the hardware supports
217 this, otherwise it is always 0. This counter is only valid if the
218 :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set.
226 - A counter of the number of transmit attempts that resulted in the
227 Not Acknowledged error. This is only set if the hardware supports
228 this, otherwise it is always 0. This counter is only valid if the
229 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set.
235 - ``tx_low_drive_cnt``
237 - A counter of the number of transmit attempts that resulted in the
238 Arbitration Lost error. This is only set if the hardware supports
239 this, otherwise it is always 0. This counter is only valid if the
240 :ref:`CEC_TX_STATUS_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set.
248 - A counter of the number of transmit errors other than Arbitration
249 Lost or Not Acknowledged. This is only set if the hardware
250 supports this, otherwise it is always 0. This counter is only
251 valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set.
257 .. tabularcolumns:: |p{2.6cm}|p{0.9cm}|p{14.0cm}|
259 .. flat-table:: CEC Transmit Status
265 - .. _`CEC-TX-STATUS-OK`:
267 - ``CEC_TX_STATUS_OK``
271 - The message was transmitted successfully. This is mutually
272 exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`. Other bits can still
273 be set if earlier attempts met with failure before the transmit
274 was eventually successful.
276 - .. _`CEC-TX-STATUS-ARB-LOST`:
278 - ``CEC_TX_STATUS_ARB_LOST``
282 - CEC line arbitration was lost.
284 - .. _`CEC-TX-STATUS-NACK`:
286 - ``CEC_TX_STATUS_NACK``
290 - Message was not acknowledged.
292 - .. _`CEC-TX-STATUS-LOW-DRIVE`:
294 - ``CEC_TX_STATUS_LOW_DRIVE``
298 - Low drive was detected on the CEC bus. This indicates that a
299 follower detected an error on the bus and requests a
302 - .. _`CEC-TX-STATUS-ERROR`:
304 - ``CEC_TX_STATUS_ERROR``
308 - Some error occurred. This is used for any errors that do not fit
309 the previous two, either because the hardware could not tell which
310 error occurred, or because the hardware tested for other
311 conditions besides those two.
313 - .. _`CEC-TX-STATUS-MAX-RETRIES`:
315 - ``CEC_TX_STATUS_MAX_RETRIES``
319 - The transmit failed after one or more retries. This status bit is
320 mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`. Other bits can still
321 be set to explain which failures were seen.
327 .. tabularcolumns:: |p{2.6cm}|p{0.9cm}|p{14.0cm}|
329 .. flat-table:: CEC Receive Status
335 - .. _`CEC-RX-STATUS-OK`:
337 - ``CEC_RX_STATUS_OK``
341 - The message was received successfully.
343 - .. _`CEC-RX-STATUS-TIMEOUT`:
345 - ``CEC_RX_STATUS_TIMEOUT``
349 - The reply to an earlier transmitted message timed out.
351 - .. _`CEC-RX-STATUS-FEATURE-ABORT`:
353 - ``CEC_RX_STATUS_FEATURE_ABORT``
357 - The message was received successfully but the reply was
358 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message
359 was the reply to an earlier transmitted message.
366 On success 0 is returned, on error -1 and the ``errno`` variable is set
367 appropriately. The generic error codes are described at the
368 :ref:`Generic Error Codes <gen-errors>` chapter.