Changed order of rules in TMK. Documented feature.

docs/feature_debounce_algo.md

@@ -0,0 +1,51 @@
+# 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 $(SPLIT_KEYBOARD)), yes)
+    # Do nothing, debouncing is inside matrix.c inside split_common
+else ifeq ($(strip $(DEBOUNCE_ALGO)), manual)
+    # Do nothing. do your debouncing in matrix.c
+else ifeq ($(strip $(DEBOUNCE_ALGO)), sym_g)
+    TMK_COMMON_SRC += $(DEBOUNCE)/debounce_sym_g.c
+else ifeq ($(strip $(DEBOUNCE_ALGO)), eager_pk)
+    TMK_COMMON_SRC += $(DEBOUNCE)/debounce_eager_pk.c
+else ifeq ($(strip $(CUSTOM_MATRIX)), yes)
+    # Do nothing. Custom matrix code.
+else # default algorithm
+    TMK_COMMON_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      |
+
+Note: 
+If ```SPLIT_KEYBOARD = YES``` is defined, the algorithm inside split_common will be used.
+A future pull request will fix this to use the debounce.c code.
+
+# 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.
+
+

tmk_core/common.mk

@@ -42,9 +42,7 @@ ifeq ($(PLATFORM),TEST)
 endif
 
 # Debounce Modules. If implemented in matrix.c, don't use these.
-ifeq ($(strip $(CUSTOM_MATRIX)), yes)
-    # Do nothing. Custom matrix code.
-else ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
+ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
     # Do nothing, debouncing is inside matrix.c inside split_common
 else ifeq ($(strip $(DEBOUNCE_ALGO)), manual)
     # Do nothing. do your debouncing in matrix.c
@@ -52,6 +50,8 @@ else ifeq ($(strip $(DEBOUNCE_ALGO)), sym_g)
     TMK_COMMON_SRC += $(DEBOUNCE)/debounce_sym_g.c
 else ifeq ($(strip $(DEBOUNCE_ALGO)), eager_pk)
     TMK_COMMON_SRC += $(DEBOUNCE)/debounce_eager_pk.c
+else ifeq ($(strip $(CUSTOM_MATRIX)), yes)
+    # Do nothing. Custom matrix code.
 else # default algorithm
     TMK_COMMON_SRC += $(DEBOUNCE)/debounce_sym_g.c
 endif