HID event queue utility
The HID event queue utility can be used by an application module to temporarily queue HID events related to keypresses (button press or release) to handle them later.
Configuration
Make sure that heap size (CONFIG_HEAP_MEM_POOL_SIZE) is large enough to handle the worst possible use case.
Data structures used to internally queue HID events are dynamically allocated using the k_malloc() function.
When no longer needed, the structures are freed using the k_free() function.
Use the CONFIG_DESKTOP_HID_EVENTQ Kconfig option to enable the utility.
You can use the utility only on HID peripherals (CONFIG_DESKTOP_ROLE_HID_PERIPHERAL).
See Kconfig help for more details.
Using HID event queue
An application module that handles keypresses internally can use this utility.
Initialization
Initialize a utility instance before use, using the hid_eventq_init() function.
Specify the limit of queued HID events to limit heap usage.
Queuing keypresses
You can use the hid_eventq_keypress_enqueue() function to enqueue a keypress event.
You can use the hid_eventq_keypress_dequeue() function to get a keypress event from the queue.
The keypress events are queued in FIFO (first in first out) manner.
An ID is used to identify the button related to the keypress.
The ID could be, for example, an application-specific identifier of a hardware button or HID usage ID.
You can use the hid_eventq_is_full() and hid_eventq_is_empty() functions, respectively, to determine if the queue is full or empty.
Clearing the queue
You can use the hid_eventq_reset() function to reset the queue.
Resetting the queue results in dropping all of the enqueued keypresses.
You can use the hid_eventq_cleanup() to remove stale keypresses (with timestamp lower than the provided minimal valid timestamp).
API documentation
Application modules can use the following API of the HID event queue:
applications/nrf_desktop/src/util/hid_eventq.happlications/nrf_desktop/src/util/hid_eventq.c