qmk_firmware/docs/feature_debounce_algo.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

ifeq ($(strip $(DEBOUNCE_ALGO)), manual)
    # Do nothing. do your debouncing in matrix.c
else ifeq ($(strip $(DEBOUNCE_ALGO)), sym_g)
    QUANTUM_SRC += $(DEBOUNCE)/debounce_sym_g.c
else ifeq ($(strip $(DEBOUNCE_ALGO)), eager_pk)
    QUANTUM_SRC += $(DEBOUNCE)/debounce_eager_pk.c
else ifeq ($(strip $(CUSTOM_MATRIX)), yes)
    # Do nothing. Custom matrix code.
else # default algorithm
    QUANTUM_SRC += $(DEBOUNCE)/debounce_sym_g.c
endif

Debounce selection

The following is for keyboards where SPLIT_KEYBOARD is not defined as YES

DEBOUNCE_ALGO	CUSTOM_MATRIX	Description	What to do
Not defined	Not defined	You are using the included matrix.c and debounce.c	Nothing. Debounce_sym_g used.
manual	Not defined	You are using the included matrix.c but your own debounce.c	SRC += debounce.c add your own debounce.c and implement necessary functions
sym_g / eager_pk	Not defined	You are using the included matrix.c and debounce.c	Nothing. Chosen debounce method used.
Not defined	YES	You have your own matrix.c, and your own debounce	Write the fully debounced matrix into matrix.c's matrix
manual	YES	Same as above	same as above
sym_g / eager_pk	YES	You are using your own matrix.c, but included debounce	Write the raw matrix values into matrix.c's matrix

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

Use your own debouncing code

• Set DEBOUNCE_ALGO = manual.
• Add SRC += debounce.c
• Add your own debounce.c. Look at included debounce.c's for sample implementations.
• Debouncing occurs after every raw matrix scan.

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.