CEC_DQEVENT — Dequeue a CEC event


int ioctl(int fd,
 int request,
 struct cec_event *argp);



File descriptor returned by open().





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 the CEC_DQEVENT ioctl. 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.

Table M.8. struct cec_event_state_change

__u16phys_addrThe current physical address.
__u16log_addr_maskThe current set of claimed logical addresses.

Table M.9. struct cec_event_lost_msgs

__u32lost_msgsSet 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.

Table M.10. struct cec_event

__u64tsTimestamp of the event in ns. 
__u32eventThe CEC event type, see Table M.11, “CEC Events Types”. 
__u32flagsEvent flags, see Table M.12, “CEC Event Flags”. 
 struct cec_event_state_changestate_changeThe new adapter state as sent by the CEC_EVENT_STATE_CHANGE event.
 struct cec_event_lost_msgslost_msgsThe number of lost messages as sent by the CEC_EVENT_LOST_MSGS event.

Table M.11. CEC Events Types

CEC_EVENT_STATE_CHANGE1Generated 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_MSGS2Generated if one or more CEC messages were lost because the application didn't dequeue CEC messages fast enough.

Table M.12. CEC Event Flags

CEC_EVENT_FL_INITIAL_VALUE1Set 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.

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.