8. ioctl CEC_DQEVENT

8.1. Name

CEC_DQEVENT - Dequeue a CEC event

8.2. Synopsis

int ioctl(int fd, CEC_DQEVENT, struct cec_event *argp)

8.3. Arguments

fd

File descriptor returned by open().

argp

8.4. Description

CEC devices can send asynchronous events. These can be retrieved by calling 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.

cec_event_state_change

struct cec_event_state_change

__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.

cec_event_lost_msgs

struct cec_event_lost_msgs

__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.

cec_event

struct cec_event

__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().
__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 Events Types

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 Flags

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.

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.