qmk_firmware/docs/feature_debounce_type.md

Debounce algorithm

QMK supports multiple debounce algorithms through its debounce API.

The underlying debounce algorithm is determined by which matrix.c file you are using.

The logic for which debounce method called is below. It checks various defines that you have set in rules.mk

DEBOUNCE_TYPE?= sym_g
VALID_DEBOUNCE_TYPES := sym_g eager_pk custom
ifeq ($(filter $(DEBOUNCE_TYPE),$(VALID_DEBOUNCE_TYPES)),)
    $(error DEBOUNCE_TYPE="$(DEBOUNCE_TYPE)" is not a valid debounce algorithm)
endif
ifeq ($(strip $(DEBOUNCE_TYPE)), sym_g)
    QUANTUM_SRC += $(DEBOUNCE_DIR)/debounce_sym_g.c
else ifeq ($(strip $(DEBOUNCE_TYPE)), eager_pk)
    QUANTUM_SRC += $(DEBOUNCE_DIR)/debounce_eager_pk.c
endif

Debounce selection

DEBOUNCE_ALGO	Description	What to do
Not defined	You are using the included matrix.c and debounce.c	Nothing. Debounce_sym_g will be compiled, and used if necessary
custom	Use your own debounce.c	SRC += debounce.c add your own debounce.c and implement necessary functions
sym_g / eager_pk	You are using the included matrix.c and debounce.c	Use an alternative debounce algorithm

Regarding split keyboards: The debounce code is compatible with split keyboards.

Use your own debouncing code

• Set DEBOUNCE_TYPE = custom .
• Add SRC += debounce.c
• Add your own debounce.c. Look at included debounce_sym_g.cs for sample implementations.
• Debouncing occurs after every raw matrix scan.
• Use num_rows rather than MATRIX_ROWS, so that split keyboards are supported correctly.

Changing between included debouncing methods

You can either use your own code, by including your own debounce.c, or switch to another included one. Included debounce methods are:

• debounce_eager_pk - debouncing per key. On any state change, response is immediate, followed by DEBOUNCE_DELAY millseconds of no further input for that key
• debounce_sym_g - debouncing per keyboard. On any state change, a global timer is set. When DEBOUNCE_DELAY milliseconds of no changes has occured, all input changes are pushed.