2.8. ioctl CEC_DQEVENT

2.8.1. Name

CEC_DQEVENT - Dequeue a CEC event

2.8.2. Synopsis

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

2.8.3. Arguments

File descriptor returned by open().


2.8.4. 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.

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.
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.
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

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.


Generated if one or more CEC messages were lost because the application didn’t dequeue CEC messages fast enough.

CEC Event Flags

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.

The ioctl CEC_DQEVENT can return the following error codes:

This is returned when the filehandle is in non-blocking mode and there are no pending events.
An interrupt (e.g. Ctrl-C) arrived while in blocking mode waiting for events to arrive.