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CEC_TX_STATUS_ERROR can be used if the HW cannot tell LOST_ARB and LOW_DRIVE apart, or when some other error occurs. It is not a replacement for NACK. So the hardware must be able to tell the difference between OK, NACK and 'something else'. Clarify the documentation (both public and kernel API) on this point. Also fix two small typos (this messages -> this message). Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
345 lines
13 KiB
ReStructuredText
345 lines
13 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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.. _CEC_TRANSMIT:
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.. _CEC_RECEIVE:
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***********************************
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ioctls CEC_RECEIVE and CEC_TRANSMIT
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***********************************
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Name
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====
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CEC_RECEIVE, CEC_TRANSMIT - Receive or transmit a CEC message
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Synopsis
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========
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.. c:function:: int ioctl( int fd, CEC_RECEIVE, struct cec_msg *argp )
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:name: CEC_RECEIVE
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.. c:function:: int ioctl( int fd, CEC_TRANSMIT, struct cec_msg *argp )
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:name: CEC_TRANSMIT
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Arguments
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=========
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``fd``
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File descriptor returned by :c:func:`open() <cec-open>`.
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``argp``
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Pointer to struct cec_msg.
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Description
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===========
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To receive a CEC message the application has to fill in the
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``timeout`` field of struct :c:type:`cec_msg` and pass it to
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:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
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If the file descriptor is in non-blocking mode and there are no received
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messages pending, then it will return -1 and set errno to the ``EAGAIN``
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error code. If the file descriptor is in blocking mode and ``timeout``
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is non-zero and no message arrived within ``timeout`` milliseconds, then
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it will return -1 and set errno to the ``ETIMEDOUT`` error code.
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A received message can be:
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1. a message received from another CEC device (the ``sequence`` field will
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be 0).
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2. the result of an earlier non-blocking transmit (the ``sequence`` field will
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be non-zero).
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To send a CEC message the application has to fill in the struct
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:c:type:`cec_msg` and pass it to :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`.
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The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is only available if
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``CEC_CAP_TRANSMIT`` is set. If there is no more room in the transmit
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queue, then it will return -1 and set errno to the ``EBUSY`` error code.
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The transmit queue has enough room for 18 messages (about 1 second worth
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of 2-byte messages). Note that the CEC kernel framework will also reply
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to core messages (see :ref:`cec-core-processing`), so it is not a good
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idea to fully fill up the transmit queue.
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If the file descriptor is in non-blocking mode then the transmit will
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return 0 and the result of the transmit will be available via
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:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` once the transmit has finished
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(including waiting for a reply, if requested).
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The ``sequence`` field is filled in for every transmit and this can be
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checked against the received messages to find the corresponding transmit
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result.
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Normally calling :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` when the physical
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address is invalid (due to e.g. a disconnect) will return ``ENONET``.
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However, the CEC specification allows sending messages from 'Unregistered' to
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'TV' when the physical address is invalid since some TVs pull the hotplug detect
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pin of the HDMI connector low when they go into standby, or when switching to
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another input.
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When the hotplug detect pin goes low the EDID disappears, and thus the
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physical address, but the cable is still connected and CEC still works.
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In order to detect/wake up the device it is allowed to send poll and 'Image/Text
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View On' messages from initiator 0xf ('Unregistered') to destination 0 ('TV').
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.. tabularcolumns:: |p{1.0cm}|p{3.5cm}|p{13.0cm}|
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.. c:type:: cec_msg
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.. cssclass:: longtable
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.. flat-table:: struct cec_msg
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 16
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* - __u64
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- ``tx_ts``
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- Timestamp in ns of when the last byte of the message was transmitted.
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The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
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the same clock from userspace use :c:func:`clock_gettime`.
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* - __u64
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- ``rx_ts``
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- Timestamp in ns of when the last byte of the message was received.
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The timestamp has been taken from the ``CLOCK_MONOTONIC`` clock. To access
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the same clock from userspace use :c:func:`clock_gettime`.
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* - __u32
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- ``len``
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- The length of the message. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in
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by the application. The driver will fill this in for
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:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be
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filled in by the driver with the length of the reply message if ``reply`` was set.
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* - __u32
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- ``timeout``
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- The timeout in milliseconds. This is the time the device will wait
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for a message to be received before timing out. If it is set to 0,
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then it will wait indefinitely when it is called by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
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If it is 0 and it is called by :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`,
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then it will be replaced by 1000 if the ``reply`` is non-zero or
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ignored if ``reply`` is 0.
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* - __u32
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- ``sequence``
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- A non-zero sequence number is automatically assigned by the CEC framework
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for all transmitted messages. It is used by the CEC framework when it queues
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the transmit result (when transmit was called in non-blocking mode). This
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allows the application to associate the received message with the original
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transmit.
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* - __u32
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- ``flags``
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- Flags. See :ref:`cec-msg-flags` for a list of available flags.
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* - __u8
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- ``tx_status``
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- The status bits of the transmitted message. See
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:ref:`cec-tx-status` for the possible status values. It is 0 if
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this message was received, not transmitted.
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* - __u8
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- ``msg[16]``
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- The message payload. For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` this is filled in by the
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application. The driver will fill this in for :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
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For :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` it will be filled in by the driver with
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the payload of the reply message if ``timeout`` was set.
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* - __u8
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- ``reply``
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- Wait until this message is replied. If ``reply`` is 0 and the
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``timeout`` is 0, then don't wait for a reply but return after
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transmitting the message. Ignored by :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
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The case where ``reply`` is 0 (this is the opcode for the Feature Abort
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message) and ``timeout`` is non-zero is specifically allowed to make it
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possible to send a message and wait up to ``timeout`` milliseconds for a
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Feature Abort reply. In this case ``rx_status`` will either be set
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to :ref:`CEC_RX_STATUS_TIMEOUT <CEC-RX-STATUS-TIMEOUT>` or
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:ref:`CEC_RX_STATUS_FEATURE_ABORT <CEC-RX-STATUS-FEATURE-ABORT>`.
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If the transmitter message is ``CEC_MSG_INITIATE_ARC`` then the ``reply``
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values ``CEC_MSG_REPORT_ARC_INITIATED`` and ``CEC_MSG_REPORT_ARC_TERMINATED``
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are processed differently: either value will match both possible replies.
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The reason is that the ``CEC_MSG_INITIATE_ARC`` message is the only CEC
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message that has two possible replies other than Feature Abort. The
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``reply`` field will be updated with the actual reply so that it is
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synchronized with the contents of the received message.
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* - __u8
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- ``rx_status``
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- The status bits of the received message. See
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:ref:`cec-rx-status` for the possible status values. It is 0 if
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this message was transmitted, not received, unless this is the
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reply to a transmitted message. In that case both ``rx_status``
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and ``tx_status`` are set.
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* - __u8
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- ``tx_status``
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- The status bits of the transmitted message. See
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:ref:`cec-tx-status` for the possible status values. It is 0 if
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this message was received, not transmitted.
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* - __u8
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- ``tx_arb_lost_cnt``
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- A counter of the number of transmit attempts that resulted in the
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Arbitration Lost error. This is only set if the hardware supports
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this, otherwise it is always 0. This counter is only valid if the
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:ref:`CEC_TX_STATUS_ARB_LOST <CEC-TX-STATUS-ARB-LOST>` status bit is set.
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* - __u8
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- ``tx_nack_cnt``
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- A counter of the number of transmit attempts that resulted in the
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Not Acknowledged error. This is only set if the hardware supports
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this, otherwise it is always 0. This counter is only valid if the
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:ref:`CEC_TX_STATUS_NACK <CEC-TX-STATUS-NACK>` status bit is set.
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* - __u8
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- ``tx_low_drive_cnt``
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- A counter of the number of transmit attempts that resulted in the
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Arbitration Lost error. This is only set if the hardware supports
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this, otherwise it is always 0. This counter is only valid if the
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:ref:`CEC_TX_STATUS_LOW_DRIVE <CEC-TX-STATUS-LOW-DRIVE>` status bit is set.
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* - __u8
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- ``tx_error_cnt``
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- A counter of the number of transmit errors other than Arbitration
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Lost or Not Acknowledged. This is only set if the hardware
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supports this, otherwise it is always 0. This counter is only
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valid if the :ref:`CEC_TX_STATUS_ERROR <CEC-TX-STATUS-ERROR>` status bit is set.
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.. tabularcolumns:: |p{6.2cm}|p{1.0cm}|p{10.3cm}|
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.. _cec-msg-flags:
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.. flat-table:: Flags for struct cec_msg
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* .. _`CEC-MSG-FL-REPLY-TO-FOLLOWERS`:
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- ``CEC_MSG_FL_REPLY_TO_FOLLOWERS``
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- 1
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- If a CEC transmit expects a reply, then by default that reply is only sent to
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the filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`. If this
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flag is set, then the reply is also sent to all followers, if any. If the
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filehandle that called :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` is also a
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follower, then that filehandle will receive the reply twice: once as the
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result of the :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>`, and once via
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:ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>`.
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.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
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.. _cec-tx-status:
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.. flat-table:: CEC Transmit Status
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 16
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* .. _`CEC-TX-STATUS-OK`:
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- ``CEC_TX_STATUS_OK``
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- 0x01
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- The message was transmitted successfully. This is mutually
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exclusive with :ref:`CEC_TX_STATUS_MAX_RETRIES <CEC-TX-STATUS-MAX-RETRIES>`. Other bits can still
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be set if earlier attempts met with failure before the transmit
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was eventually successful.
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* .. _`CEC-TX-STATUS-ARB-LOST`:
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- ``CEC_TX_STATUS_ARB_LOST``
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- 0x02
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- CEC line arbitration was lost.
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* .. _`CEC-TX-STATUS-NACK`:
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- ``CEC_TX_STATUS_NACK``
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- 0x04
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- Message was not acknowledged.
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* .. _`CEC-TX-STATUS-LOW-DRIVE`:
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- ``CEC_TX_STATUS_LOW_DRIVE``
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- 0x08
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- Low drive was detected on the CEC bus. This indicates that a
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follower detected an error on the bus and requests a
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retransmission.
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* .. _`CEC-TX-STATUS-ERROR`:
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- ``CEC_TX_STATUS_ERROR``
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- 0x10
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- Some error occurred. This is used for any errors that do not fit
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``CEC_TX_STATUS_ARB_LOST`` or ``CEC_TX_STATUS_LOW_DRIVE``, either because
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the hardware could not tell which error occurred, or because the hardware
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tested for other conditions besides those two.
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* .. _`CEC-TX-STATUS-MAX-RETRIES`:
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- ``CEC_TX_STATUS_MAX_RETRIES``
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- 0x20
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- The transmit failed after one or more retries. This status bit is
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mutually exclusive with :ref:`CEC_TX_STATUS_OK <CEC-TX-STATUS-OK>`. Other bits can still
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be set to explain which failures were seen.
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.. tabularcolumns:: |p{5.6cm}|p{0.9cm}|p{11.0cm}|
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.. _cec-rx-status:
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.. flat-table:: CEC Receive Status
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 16
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* .. _`CEC-RX-STATUS-OK`:
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- ``CEC_RX_STATUS_OK``
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- 0x01
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- The message was received successfully.
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* .. _`CEC-RX-STATUS-TIMEOUT`:
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- ``CEC_RX_STATUS_TIMEOUT``
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- 0x02
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- The reply to an earlier transmitted message timed out.
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* .. _`CEC-RX-STATUS-FEATURE-ABORT`:
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- ``CEC_RX_STATUS_FEATURE_ABORT``
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- 0x04
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- The message was received successfully but the reply was
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``CEC_MSG_FEATURE_ABORT``. This status is only set if this message
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was the reply to an earlier transmitted message.
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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The :ref:`ioctl CEC_RECEIVE <CEC_RECEIVE>` can return the following
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error codes:
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EAGAIN
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No messages are in the receive queue, and the filehandle is in non-blocking mode.
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ETIMEDOUT
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The ``timeout`` was reached while waiting for a message.
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ERESTARTSYS
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The wait for a message was interrupted (e.g. by Ctrl-C).
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The :ref:`ioctl CEC_TRANSMIT <CEC_TRANSMIT>` can return the following
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error codes:
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ENOTTY
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The ``CEC_CAP_TRANSMIT`` capability wasn't set, so this ioctl is not supported.
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EPERM
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The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>`
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has never been called.
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ENONET
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The CEC adapter is not configured, i.e. :ref:`ioctl CEC_ADAP_S_LOG_ADDRS <CEC_ADAP_S_LOG_ADDRS>`
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was called, but the physical address is invalid so no logical address was claimed.
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An exception is made in this case for transmits from initiator 0xf ('Unregistered')
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to destination 0 ('TV'). In that case the transmit will proceed as usual.
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EBUSY
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Another filehandle is in exclusive follower or initiator mode, or the filehandle
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is in mode ``CEC_MODE_NO_INITIATOR``. This is also returned if the transmit
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queue is full.
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EINVAL
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The contents of struct :c:type:`cec_msg` is invalid.
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ERESTARTSYS
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The wait for a successful transmit was interrupted (e.g. by Ctrl-C).
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