CEC_RECEIVE, CEC_TRANSMIT — Receive or transmit a CEC message
int ioctl( | int fd, |
| int request, | |
struct cec_msg *argp); |
Note: this documents the proposed CEC API. This API is not yet finalized and is currently only available as a staging kernel module.
To receive a CEC message the application has to fill in the
cec_msg structure and pass it to the
CEC_RECEIVE ioctl. CEC_RECEIVE is
only available if CEC_CAP_RECEIVE is set. If the
file descriptor is in non-blocking mode and there are no received
messages pending, then it will return -1 and set errno to the EAGAIN error code.
If the file descriptor is in blocking mode and timeout
is non-zero and no message arrived within timeout
milliseconds, then it will return -1 and set errno to the ETIMEDOUT error code.
To send a CEC message the application has to fill in the
cec_msg structure and pass it to the
CEC_TRANSMIT ioctl. CEC_TRANSMIT is
only available if CEC_CAP_TRANSMIT is set.
If there is no more room in the transmit queue, then it will return
-1 and set errno to the EBUSY error code.
Table M.16. struct cec_msg
| __u64 | ts | Timestamp of when the message was transmitted in ns in the case
of CEC_TRANSMIT with reply
set to 0, or the timestamp of the received message in all other cases. |
| __u32 | len | The length of the message. For CEC_TRANSMIT this
is filled in by the application. The driver will fill this in for
CEC_RECEIVE and for CEC_TRANSMIT
it will be filled in with the length of the reply message if
reply was set. |
| __u32 | timeout | The timeout in milliseconds. This is the time the device will wait for a message to
be received before timing out. If it is set to 0, then it will wait indefinitely when it
is called by CEC_RECEIVE. If it is 0 and it is called by
CEC_TRANSMIT, then it will be replaced by 1000 if the
reply is non-zero or ignored if reply
is 0. |
| __u32 | sequence | The sequence number is automatically assigned by the CEC framework for all transmitted messages. It can be later used by the framework to generate an event if a reply for a message was requested and the message was transmitted in a non-blocking mode. |
| __u32 | flags | Flags. No flags are defined yet, so set this to 0. |
| __u8 | rx_status | The status bits of the received message. See Table M.18, “CEC Receive Status”
for the possible status values. It is 0 if this message was transmitted, not
received, unless this is the reply to a transmitted message. In that case both
rx_status and tx_status
are set. |
| __u8 | tx_status | The status bits of the transmitted message. See Table M.17, “CEC Transmit Status” for the possible status values. It is 0 if this messages was received, not transmitted. |
| __u8 | msg[16] | The message payload. For CEC_TRANSMIT this
is filled in by the application. The driver will fill this in for
CEC_RECEIVE and for CEC_TRANSMIT
it will be filled in with the payload of the reply message if
reply was set. |
| __u8 | reply | Wait until this message is replied. If reply
is 0 and the timeout is 0, then don't wait for a reply but
return after transmitting the message. If there was an error as indicated by a non-zero
tx_status field, then reply and
timeout are both set to 0 by the driver. Ignored by
CEC_RECEIVE. The case where reply is 0
(this is the opcode for the Feature Abort message) and timeout
is non-zero is specifically allowed to send a message and wait up to timeout
milliseconds for a Feature Abort reply. In this case rx_status
will either be set to CEC_RX_STATUS_TIMEOUT or
CEC_RX_STATUS_FEATURE_ABORT. |
| __u8 | tx_arb_lost_cnt | A counter of the number of transmit attempts that resulted in the
Arbitration Lost error. This is only set if the hardware supports this, otherwise
it is always 0. This counter is only valid if the CEC_TX_STATUS_ARB_LOST
status bit is set. |
| __u8 | tx_nack_cnt | A counter of the number of transmit attempts that resulted in the
Not Acknowledged error. This is only set if the hardware supports this, otherwise
it is always 0. This counter is only valid if the CEC_TX_STATUS_NACK
status bit is set. |
| __u8 | tx_low_drive_cnt | A counter of the number of transmit attempts that resulted in the
Arbitration Lost error. This is only set if the hardware supports this, otherwise
it is always 0. This counter is only valid if the CEC_TX_STATUS_LOW_DRIVE
status bit is set. |
| __u8 | tx_error_cnt | A counter of the number of transmit errors other than Arbitration Lost
or Not Acknowledged. This is only set if the hardware supports this, otherwise
it is always 0. This counter is only valid if the CEC_TX_STATUS_ERROR
status bit is set. |
Table M.17. CEC Transmit Status
CEC_TX_STATUS_OK | 0x01 | The message was transmitted successfully. This is mutually exclusive with
CEC_TX_STATUS_MAX_RETRIES. Other bits can still be set if
earlier attempts met with failure before the transmit was eventually successful. |
CEC_TX_STATUS_ARB_LOST | 0x02 | CEC line arbitration was lost. |
CEC_TX_STATUS_NACK | 0x04 | Message was not acknowledged. |
CEC_TX_STATUS_LOW_DRIVE | 0x08 | Low drive was detected on the CEC bus. This indicates that a follower detected an error on the bus and requests a retransmission. |
CEC_TX_STATUS_ERROR | 0x10 | Some error occurred. This is used for any errors that do not fit the previous two, either because the hardware could not tell which error occurred, or because the hardware tested for other conditions besides those two. |
CEC_TX_STATUS_MAX_RETRIES | 0x20 | The transmit failed after one or more retries. This status bit is mutually
exclusive with CEC_TX_STATUS_OK. Other bits can still be set
to explain which failures were seen. |
Table M.18. CEC Receive Status
CEC_RX_STATUS_OK | 0x01 | The message was received successfully. |
CEC_RX_STATUS_TIMEOUT | 0x02 | The reply to an earlier transmitted message timed out. |
CEC_RX_STATUS_FEATURE_ABORT | 0x04 | The message was received successfully but the reply was
CEC_MSG_FEATURE_ABORT. This status is only
set if this message was the reply to an earlier transmitted
message. |
On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.