Debounce refactor / API (#3720)

* Added xeal60 via clone of lets split

* Delete removed other keymaps

* Basic keymap (no FN). Compiles.

* Removed NP_STAR and NP_SLSH.

* Removed "debounce_algo = manual" in all keyboards with CUSTOM_MATRIX = yes.

* Changed order of rules in TMK. Documented feature.

* Fixed missing whitespace in debounce documentation

Table wasn't working due to missing newline.

* Added bold in a few areas.

* DO NOT USE - Removed debounce from TMK.

* Remove accidental xeal60 commit

* DO NOT USE - debounce successfully compiled.

* DO NOT USE Revert back to original API to support split_keyboards.

* Working eager_pk

* Whitespace cleanup.

* Restored debounce.h since there wasnt any real change.

* Moved debouncing_time variable  to inside #if debounce

* Removed check for custom_matrix. We can safely include the debounce file for compilation when custom_matrix is used.

* Removed #include "matrix.h" from debounce.h

* Bug fix - was using MATRIX_ROWS instead of num_rows

* Fixed compilation error with debounce_sym_g

* Renamed DEBOUNCE_ALGO to DEBOUNCE_TYPE

* Malloc array in debounce_eager_pk, since split keyboards only use MATRIX_ROWS/2.

* Fix compile error in debounce_eager_pk

* Stricter, leaner DEBOUNCE_TYPE section in common_features.mk. Cleanup debounce_type.mk

1 files changed, 46 insertions, 0 deletions

diff --git a/docs/feature_debounce_type.md b/docs/feature_debounce_type.md
new file mode 100644
index 0000000000..82b3d7de12
--- /dev/null
+++ b/docs/feature_debounce_type.md
@@ -0,0 +1,46 @@
+# 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.c```s 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.
+
+