371 lines
10 KiB
ReStructuredText
371 lines
10 KiB
ReStructuredText
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.. -*- 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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.. note::
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This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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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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.. 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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- .. row 1
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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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- .. row 2
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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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- .. row 3
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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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- .. row 4
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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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- .. row 5
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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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- .. row 6
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- __u32
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- ``flags``
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- Flags. No flags are defined yet, so set this to 0.
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- .. row 7
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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 messages was received, not transmitted.
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- .. row 8
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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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- .. row 8
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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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- .. row 9
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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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- .. row 10
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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 messages was received, not transmitted.
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- .. row 11
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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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- .. row 12
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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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- .. row 13
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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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- .. row 14
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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{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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the previous two, either because the hardware could not tell which
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error occurred, or because the hardware tested for other
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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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