2.8. ioctl CEC_DQEVENT¶
2.8.1. Name¶
CEC_DQEVENT - Dequeue a CEC event
2.8.4. Description¶
Note
This documents the proposed CEC API. This API is not yet finalized and is currently only available as a staging kernel module.
CEC devices can send asynchronous events. These can be retrieved by
calling ioctl CEC_DQEVENT. If the file descriptor is in
non-blocking mode and no event is pending, then it will return -1 and
set errno to the EAGAIN
error code.
The internal event queues are per-filehandle and per-event type. If there is no more room in a queue then the last event is overwritten with the new one. This means that intermediate results can be thrown away but that the latest event is always available. This also means that is it possible to read two successive events that have the same value (e.g. two CEC_EVENT_STATE_CHANGE events with the same state). In that case the intermediate state changes were lost but it is guaranteed that the state did change in between the two events.
__u16 | phys_addr |
The current physical address. This is CEC_PHYS_ADDR_INVALID if no
valid physical address is set. |
__u16 | log_addr_mask |
The current set of claimed logical addresses. This is 0 if no logical
addresses are claimed or if phys_addr is CEC_PHYS_ADDR_INVALID .
If bit 15 is set (1 << CEC_LOG_ADDR_UNREGISTERED ) then this device
has the unregistered logical address. In that case all other bits are 0. |
__u32 | lost_msgs |
Set to the number of lost messages since the filehandle was opened or since the last time this event was dequeued for this filehandle. The messages lost are the oldest messages. So when a new message arrives and there is no more room, then the oldest message is discarded to make room for the new one. The internal size of the message queue guarantees that all messages received in the last two seconds will be stored. Since messages should be replied to within a second according to the CEC specification, this is more than enough. |
__u64 | ts |
Timestamp of the event in ns.
The timestamp has been taken from the CLOCK_MONOTONIC clock. To access
the same clock from userspace use clock_gettime(2)() . |
|
__u32 | event |
The CEC event type, see CEC Events Types. | |
__u32 | flags |
Event flags, see CEC Event Flags. | |
union | (anonymous) | ||
struct cec_event_state_change | state_change |
The new adapter state as sent by the CEC_EVENT_STATE_CHANGE event. | |
struct cec_event_lost_msgs | lost_msgs |
The number of lost messages as sent by the CEC_EVENT_LOST_MSGS event. |
CEC_EVENT_STATE_CHANGE |
1 | Generated when the CEC Adapter’s state changes. When open() is called an initial event will be generated for that filehandle with the CEC Adapter’s state at that time. |
CEC_EVENT_LOST_MSGS |
2 | Generated if one or more CEC messages were lost because the application didn’t dequeue CEC messages fast enough. |
CEC_EVENT_FL_INITIAL_VALUE |
1 | Set for the initial events that are generated when the device is opened. See the table above for which events do this. This allows applications to learn the initial state of the CEC adapter at open() time. |
2.8.5. Return Value¶
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.