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 :c:type:`struct cec_msg` and pass it to :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
44 If the file descriptor is in non-blocking mode and there are no received
45 messages pending, then it will return -1 and set errno to the ``EAGAIN``
46 error code. If the file descriptor is in blocking mode and ``timeout``
47 is non-zero and no message arrived within ``timeout`` milliseconds, then
48 it will return -1 and set errno to the ``ETIMEDOUT`` error code.
50 A received message can be:
52 1. a message received from another CEC device (the ``sequence`` field will
54 2. the result of an earlier non-blocking transmit (the ``sequence`` field will
57 To send a CEC message the application has to fill in the
58 :c:type:`struct cec_msg` and pass it to
59 :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is only available if
60 ``CEC_CAP_TRANSMIT`` is set. If there is no more room in the transmit
61 queue, then it will return -1 and set errno to the ``EBUSY`` error code.
62 The transmit queue has enough room for 18 messages (about 1 second worth
63 of 2-byte messages). Note that the CEC kernel framework will also reply
64 to core messages (see :ref:cec-core-processing), so it is not a good
65 idea to fully fill up the transmit queue.
67 If the file descriptor is in non-blocking mode then the transmit will
68 return 0 and the result of the transmit will be available via
69 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` once the transmit has finished
70 (including waiting for a reply, if requested).
72 The ``sequence`` field is filled in for every transmit and this can be
73 checked against the received messages to find the corresponding transmit
77 .. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{13.0cm}|
81 .. cssclass:: longtable
83 .. flat-table:: struct cec_msg
95 - Timestamp in ns of when the last byte of the message was transmitted.
96 The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
97 the same clock from userspace use :c:func:`clock_gettime(2)`.
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(2)`.
115 - The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in
116 by the application. The driver will fill this in for
117 :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be
118 filled in by the driver with the length of the reply message if ``reply`` was set.
126 - The timeout in milliseconds. This is the time the device will wait
127 for a message to be received before timing out. If it is set to 0,
128 then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
129 If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`,
130 then it will be replaced by 1000 if the ``reply`` is non-zero or
131 ignored if ``reply`` is 0.
139 - A non-zero sequence number is automatically assigned by the CEC framework
140 for all transmitted messages. It is used by the CEC framework when it queues
141 the transmit result (when transmit was called in non-blocking mode). This
142 allows the application to associate the received message with the original
151 - Flags. No flags are defined yet, so set this to 0.
159 - The status bits of the transmitted message. See
160 :ref:`cec-tx-status` for the possible status values. It is 0 if
161 this messages was received, not transmitted.
169 - The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the
170 application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
171 For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with
172 the payload of the reply message if ``timeout`` was set.
180 - Wait until this message is replied. If ``reply`` is 0 and the
181 ``timeout`` is 0, then don't wait for a reply but return after
182 transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
183 The case where ``reply`` is 0 (this is the opcode for the Feature Abort
184 message) and ``timeout`` is non-zero is specifically allowed to make it
185 possible to send a message and wait up to ``timeout`` milliseconds for a
186 Feature Abort reply. In this case ``rx_status`` will either be set
187 to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or
188 :ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`.
196 - The status bits of the received message. See
197 :ref:`cec-rx-status` for the possible status values. It is 0 if
198 this message was transmitted, not received, unless this is the
199 reply to a transmitted message. In that case both ``rx_status``
200 and ``tx_status`` are set.
208 - The status bits of the transmitted message. See
209 :ref:`cec-tx-status` for the possible status values. It is 0 if
210 this messages was received, not transmitted.
216 - ``tx_arb_lost_cnt``
218 - A counter of the number of transmit attempts that resulted in the
219 Arbitration Lost error. This is only set if the hardware supports
220 this, otherwise it is always 0. This counter is only valid if the
221 :ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set.
229 - A counter of the number of transmit attempts that resulted in the
230 Not Acknowledged error. This is only set if the hardware supports
231 this, otherwise it is always 0. This counter is only valid if the
232 :ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set.
238 - ``tx_low_drive_cnt``
240 - A counter of the number of transmit attempts that resulted in the
241 Arbitration Lost error. This is only set if the hardware supports
242 this, otherwise it is always 0. This counter is only valid if the
243 :ref:`CEC_TX_STATUS_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set.
251 - A counter of the number of transmit errors other than Arbitration
252 Lost or Not Acknowledged. This is only set if the hardware
253 supports this, otherwise it is always 0. This counter is only
254 valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set.
257 .. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
261 .. flat-table:: CEC Transmit Status
267 - .. _`CEC-TX-STATUS-OK`:
269 - ``CEC_TX_STATUS_OK``
273 - The message was transmitted successfully. This is mutually
274 exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`. Other bits can still
275 be set if earlier attempts met with failure before the transmit
276 was eventually successful.
278 - .. _`CEC-TX-STATUS-ARB-LOST`:
280 - ``CEC_TX_STATUS_ARB_LOST``
284 - CEC line arbitration was lost.
286 - .. _`CEC-TX-STATUS-NACK`:
288 - ``CEC_TX_STATUS_NACK``
292 - Message was not acknowledged.
294 - .. _`CEC-TX-STATUS-LOW-DRIVE`:
296 - ``CEC_TX_STATUS_LOW_DRIVE``
300 - Low drive was detected on the CEC bus. This indicates that a
301 follower detected an error on the bus and requests a
304 - .. _`CEC-TX-STATUS-ERROR`:
306 - ``CEC_TX_STATUS_ERROR``
310 - Some error occurred. This is used for any errors that do not fit
311 the previous two, either because the hardware could not tell which
312 error occurred, or because the hardware tested for other
313 conditions besides those two.
315 - .. _`CEC-TX-STATUS-MAX-RETRIES`:
317 - ``CEC_TX_STATUS_MAX_RETRIES``
321 - The transmit failed after one or more retries. This status bit is
322 mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`. Other bits can still
323 be set to explain which failures were seen.
326 .. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
330 .. flat-table:: CEC Receive Status
336 - .. _`CEC-RX-STATUS-OK`:
338 - ``CEC_RX_STATUS_OK``
342 - The message was received successfully.
344 - .. _`CEC-RX-STATUS-TIMEOUT`:
346 - ``CEC_RX_STATUS_TIMEOUT``
350 - The reply to an earlier transmitted message timed out.
352 - .. _`CEC-RX-STATUS-FEATURE-ABORT`:
354 - ``CEC_RX_STATUS_FEATURE_ABORT``
358 - The message was received successfully but the reply was
359 ``CEC_MSG_FEATURE_ABORT``. This status is only set if this message
360 was the reply to an earlier transmitted message.
367 On success 0 is returned, on error -1 and the ``errno`` variable is set
368 appropriately. The generic error codes are described at the
369 :ref:`Generic Error Codes <gen-errors>` chapter.