Simplify split_common Code significantly (#4772)

* Eliminate separate slave loop

Both master and slave run the standard keyboard_task main loop now.

* Refactor i2c/serial specific code

Simplify some of the preprocessor mess by using common function names.

* Fix missing #endif

* Move direct pin mapping support from miniaxe to split_common

For boards with more pins than sense--sorry, switches.

* Reordering and reformatting only

* Don't run matrix_scan_quantum on slave side

* Clean up the offset/slaveOffset calculations

* Cut undebounced matrix size in half

* Refactor debouncing

* Minor fixups

* Split split_common transport and debounce code into their own files

Can now be replaced with custom versions per keyboard using
CUSTOM_TRANSPORT = yes and CUSTOM_DEBOUNCE = yes

* Refactor debounce for non-split keyboards too

* Update handwired/xealous to build using new split_common

* Fix debounce breaking basic test

* Dodgy method to allow a split kb to only include one of i2c/serial

SPLIT_TRANSPORT = serial or SPLIT_TRANSPORT = i2c will include only
that driver code in the binary.

SPLIT_TRANSPORT = custom (or anything else) will include neither, the
keyboard must supply it's own code

if SPLIT_TRANSPORT is not defined then the original behaviour (include
both avr i2c and serial code) is maintained.

This could be better but it would require explicitly updating all the
existing split keyboards.

* Enable LTO to get lets_split/sockets under the line

* Add docs for SPLIT_TRANSPORT, CUSTOM_MATRIX, CUSTOM_DEBOUNCE

* Remove avr-specific sei() from split matrix_setup

Not needed now that slave doesn't have a separate main loop.
Both sides (on avr) call sei() in lufa's main() after exiting
keyboard_setup().

* Fix QUANTUM_LIB_SRC references and simplify SPLIT_TRANSPORT.

* Add comments and fix formatting.

24 files changed, 711 insertions, 1321 deletions

diff --git a/common_features.mk b/common_features.mk
index 572a6db548..8c3361732c 100644
--- a/common_features.mk
+++ b/common_features.mk
@@ -254,20 +254,34 @@ QUANTUM_SRC:= \
     $(QUANTUM_DIR)/keymap_common.c \
     $(QUANTUM_DIR)/keycode_config.c
 
-ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
-    ifneq ($(strip $(CUSTOM_MATRIX)), yes)
-       QUANTUM_SRC += $(QUANTUM_DIR)/split_common/matrix.c
-       # Do not use $(QUANTUM_DIR)/matrix.c.
-       CUSTOM_MATRIX=yes
+# Include the standard or split matrix code if needed
+ifneq ($(strip $(CUSTOM_MATRIX)), yes)
+    ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
+        QUANTUM_SRC += $(QUANTUM_DIR)/split_common/matrix.c
+    else
+        QUANTUM_SRC += $(QUANTUM_DIR)/matrix.c
     endif
+endif
+
+# Include the standard debounce code if needed
+ifneq ($(strip $(CUSTOM_DEBOUNCE)), yes)
+    QUANTUM_SRC += $(QUANTUM_DIR)/debounce.c
+endif
+
+ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
     OPT_DEFS += -DSPLIT_KEYBOARD
+
+    # Include files used by all split keyboards
     QUANTUM_SRC += $(QUANTUM_DIR)/split_common/split_flags.c \
-                $(QUANTUM_DIR)/split_common/split_util.c
-    QUANTUM_LIB_SRC += $(QUANTUM_DIR)/split_common/i2c.c
-    QUANTUM_LIB_SRC += $(QUANTUM_DIR)/split_common/serial.c
+                   $(QUANTUM_DIR)/split_common/split_util.c
+
+    # Determine which (if any) transport files are required
+    ifneq ($(strip $(SPLIT_TRANSPORT)), custom)
+        QUANTUM_SRC += $(QUANTUM_DIR)/split_common/transport.c
+        # Functions added via QUANTUM_LIB_SRC are only included in the final binary if they're called.
+        # Unused functions are pruned away, which is why we can add both drivers here without bloat.
+        QUANTUM_LIB_SRC += $(QUANTUM_DIR)/split_common/i2c.c \
+                           $(QUANTUM_DIR)/split_common/serial.c
+    endif
     COMMON_VPATH += $(QUANTUM_PATH)/split_common
 endif
-
-ifneq ($(strip $(CUSTOM_MATRIX)), yes)
-    QUANTUM_SRC += $(QUANTUM_DIR)/matrix.c
-endif
diff --git a/docs/config_options.md b/docs/config_options.md
index 63bcc41d0a..f5c2e76e7e 100644
--- a/docs/config_options.md
+++ b/docs/config_options.md
@@ -143,7 +143,7 @@ If you define these options you will enable the associated feature, which may in
   * Breaks any Tap Toggle functionality (`TT` or the One Shot Tap Toggle)
 * `#define LEADER_TIMEOUT 300`
   * how long before the leader key times out
-    * If you're having issues finishing the sequence before it times out, you may need to increase the timeout setting. Or you may want to enable the `LEADER_PER_KEY_TIMING` option, which resets the timeout after each key is tapped. 
+    * If you're having issues finishing the sequence before it times out, you may need to increase the timeout setting. Or you may want to enable the `LEADER_PER_KEY_TIMING` option, which resets the timeout after each key is tapped.
 * `#define LEADER_PER_KEY_TIMING`
   * sets the timer for leader key chords to run on each key press rather than overall
 * `#define LEADER_KEY_STRICT_KEY_PROCESSING`
@@ -197,6 +197,9 @@ If you define these options you will enable the associated feature, which may in
 
 Split Keyboard specific options, make sure you have 'SPLIT_KEYBOARD = yes' in your rules.mk
 
+* `SPLIT_TRANSPORT = custom`
+  * Allows replacing the standard split communication routines with a custom one. ARM based split keyboards must use this at present.
+
 ### Setting Handedness
 
 One thing to remember, the side that the USB port is plugged into is always the master half. The side not plugged into USB is the slave.
@@ -208,7 +211,7 @@ There are a few different ways to set handedness for split keyboards (listed in
 3. Set `MASTER_RIGHT`: Half that is plugged into the USB port is determined to be the master and right half (inverse of the default)
 4. Default: The side that is plugged into the USB port is the master half and is assumed to be the left half. The slave side is the right half
 
-* `#define SPLIT_HAND_PIN B7` 
+* `#define SPLIT_HAND_PIN B7`
   * For using high/low pin to determine handedness, low = right hand, high = left hand. Replace `B7` with the pin you are using. This is optional, and if you leave `SPLIT_HAND_PIN` undefined, then you can still use the EE_HANDS method or MASTER_LEFT / MASTER_RIGHT defines like the stock Let's Split uses.
 
 * `#define EE_HANDS` (only works if `SPLIT_HAND_PIN` is not defined)
@@ -302,6 +305,10 @@ Use these to enable or disable building certain features. The more you have enab
   * Current options are AdafruitEzKey, AdafruitBLE, RN42
 * `SPLIT_KEYBOARD`
   * Enables split keyboard support (dual MCU like the let's split and bakingpy's boards) and includes all necessary files located at quantum/split_common
+* `CUSTOM_MATRIX`
+  * Allows replacing the standard matrix scanning routine with a custom one.
+* `CUSTOM_DEBOUNCE`
+  * Allows replacing the standard key debouncing routine with a custom one.
 * `WAIT_FOR_USB`
   * Forces the keyboard to wait for a USB connection to be established before it starts up
 * `NO_USB_STARTUP_CHECK`
diff --git a/docs/getting_started_make_guide.md b/docs/getting_started_make_guide.md
index adc1aed751..bb7e1e7e3b 100644
--- a/docs/getting_started_make_guide.md
+++ b/docs/getting_started_make_guide.md
@@ -97,7 +97,7 @@ This allows you to send Unicode characters using `UC(<code point>)` in your keym
 
 `UNICODEMAP_ENABLE`
 
-This allows you to send Unicode characters using `X(<map index>)` in your keymap. You will need to maintain a mapping table in your keymap file. All possible code points (up to `0x10FFFF`) are supported. 
+This allows you to send Unicode characters using `X(<map index>)` in your keymap. You will need to maintain a mapping table in your keymap file. All possible code points (up to `0x10FFFF`) are supported.
 
 `UCIS_ENABLE`
 
@@ -135,6 +135,18 @@ This enables [key lock](feature_key_lock.md). This consumes an additional 260 by
 
 This enables split keyboard support (dual MCU like the let's split and bakingpy's boards) and includes all necessary files located at quantum/split_common
 
+`SPLIT_TRANSPORT`
+
+As there is no standard split communication driver for ARM-based split keyboards yet, `SPLIT_TRANSPORT = custom` must be used for these. It will prevent the standard split keyboard communication code (which is AVR-specific) from being included, allowing a custom implementation to be used.
+
+`CUSTOM_MATRIX`
+
+Lets you replace the default matrix scanning routine with your own code. You will need to provide your own implementations of matrix_init() and matrix_scan().
+
+`CUSTOM_DEBOUNCE`
+
+Lets you replace the default key debouncing routine with your own code. You will need to provide your own implementation of debounce().
+
 ## Customizing Makefile Options on a Per-Keymap Basis
 
 If your keymap directory has a file called `rules.mk` any options you set in that file will take precedence over other `rules.mk` options for your particular keyboard.
diff --git a/keyboards/handwired/xealous/debounce.c b/keyboards/handwired/xealous/debounce.c
new file mode 100644
index 0000000000..65a99f27f2
--- /dev/null
+++ b/keyboards/handwired/xealous/debounce.c
@@ -0,0 +1,63 @@
+#include <string.h>
+#include "config.h"
+#include "matrix.h"
+#include "timer.h"
+#include "quantum.h"
+
+#ifndef DEBOUNCING_DELAY
+#   define DEBOUNCING_DELAY 5
+#endif
+
+//Debouncing counters
+typedef uint8_t debounce_counter_t;
+#define DEBOUNCE_COUNTER_MODULO 250
+#define DEBOUNCE_COUNTER_INACTIVE 251
+
+static debounce_counter_t *debounce_counters;
+
+void debounce_init(uint8_t num_rows)
+{
+  debounce_counters = malloc(num_rows*MATRIX_COLS);
+  memset(debounce_counters, DEBOUNCE_COUNTER_INACTIVE, num_rows*MATRIX_COLS);
+}
+
+void update_debounce_counters(uint8_t num_rows, uint8_t current_time)
+{
+  for (uint8_t row = 0; row < num_rows; row++)
+  {
+    for (uint8_t col = 0; col < MATRIX_COLS; col++)
+    {
+      if (debounce_counters[row*MATRIX_COLS + col] != DEBOUNCE_COUNTER_INACTIVE)
+      {
+        if (TIMER_DIFF(current_time, debounce_counters[row*MATRIX_COLS + col], DEBOUNCE_COUNTER_MODULO) >= DEBOUNCING_DELAY) {
+          debounce_counters[row*MATRIX_COLS + col] = DEBOUNCE_COUNTER_INACTIVE;
+        }
+      }
+    }
+  }
+}
+
+void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t current_time)
+{
+    for (uint8_t row = 0; row < num_rows; row++)
+    {
+      matrix_row_t delta = raw[row] ^ cooked[row];
+
+      for (uint8_t col = 0; col < MATRIX_COLS; col++)
+      {
+          if (debounce_counters[row*MATRIX_COLS + col] == DEBOUNCE_COUNTER_INACTIVE && (delta & (1<<col)))
+          {
+              debounce_counters[row*MATRIX_COLS + col] = current_time;
+              cooked[row] ^= (1 << col);
+          }
+      }
+    }
+}
+
+void debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed)
+{
+    uint8_t current_time = timer_read() % DEBOUNCE_COUNTER_MODULO;
+
+    update_debounce_counters(num_rows, current_time);
+    transfer_matrix_values(raw, cooked, num_rows, current_time);
+}
\ No newline at end of file
diff --git a/keyboards/handwired/xealous/rules.mk b/keyboards/handwired/xealous/rules.mk
index eebd11d86e..07e1c875e6 100644
--- a/keyboards/handwired/xealous/rules.mk
+++ b/keyboards/handwired/xealous/rules.mk
@@ -1,4 +1,5 @@
-SRC += matrix_scanrate.c matrix.c 
+#SRC += matrix_scanrate.c matrix.c
+SRC += debounce.c
 
 # MCU name
 MCU = atmega32u4
@@ -37,7 +38,7 @@ F_USB = $(F_CPU)
 
 # Bootloader
 #     This definition is optional, and if your keyboard supports multiple bootloaders of
-#     different sizes, comment this out, and the correct address will be loaded 
+#     different sizes, comment this out, and the correct address will be loaded
 #     automatically (+60). See bootloader.mk for all options.
 BOOTLOADER = caterina
 
@@ -59,14 +60,15 @@ MIDI_ENABLE = no            # MIDI controls
 AUDIO_ENABLE = yes          # Audio output on port C6
 UNICODE_ENABLE = no         # Unicode
 BLUETOOTH_ENABLE = no       # Enable Bluetooth with the Adafruit EZ-Key HID
-RGBLIGHT_ENABLE = no        # Enable WS2812 RGB underlight. 
+RGBLIGHT_ENABLE = no        # Enable WS2812 RGB underlight.
 SPLIT_KEYBOARD = yes        # Use shared split_common code
 SUBPROJECT_rev1 = yes
 
 # Do not enable SLEEP_LED_ENABLE. it uses the same timer as BACKLIGHT_ENABLE
 SLEEP_LED_ENABLE = no    # Breathing sleep LED during USB suspend
 
-CUSTOM_MATRIX = yes
+CUSTOM_MATRIX = no
+CUSTOM_DEBOUNCE = yes
 
 LAYOUTS = split60
 
diff --git a/keyboards/lets_split/sockets/config.h b/keyboards/lets_split/sockets/config.h
index 6939d37dc5..e73c45722d 100644
--- a/keyboards/lets_split/sockets/config.h
+++ b/keyboards/lets_split/sockets/config.h
@@ -85,3 +85,12 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 //#define NO_ACTION_ONESHOT
 //#define NO_ACTION_MACRO
 //#define NO_ACTION_FUNCTION
+
+#ifdef USE_Link_Time_Optimization
+  // LTO has issues with macros (action_get_macro) and "functions" (fn_actions),
+  //  so just disable them
+  #define NO_ACTION_MACRO
+  #define NO_ACTION_FUNCTION
+
+  #define DISABLE_LEADER
+#endif // USE_Link_Time_Optimization
\ No newline at end of file
diff --git a/keyboards/lets_split/sockets/rules.mk b/keyboards/lets_split/sockets/rules.mk
index e14d18d8de..da04decf40 100644
--- a/keyboards/lets_split/sockets/rules.mk
+++ b/keyboards/lets_split/sockets/rules.mk
@@ -1,3 +1,5 @@
 BACKLIGHT_ENABLE = no
 AUDIO_ENABLE = yes
 RGBLIGHT_ENABLE = yes #Don't enable this along with I2C
+
+EXTRAFLAGS += -flto -DUSE_Link_Time_Optimization
diff --git a/keyboards/miniaxe/config.h b/keyboards/miniaxe/config.h
index 2b732ca16f..7a68476a54 100644
--- a/keyboards/miniaxe/config.h
+++ b/keyboards/miniaxe/config.h
@@ -44,8 +44,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 // #define MATRIX_ROW_PINS { D0, D5 }
 // #define MATRIX_COL_PINS { F1, F0, B0 }
-#define NO_PIN 0xFF
-#define MATRIX_ROW_COL_PINS { \
+#define DIRECT_PINS { \
     { F1, E6, B0, B2, B3 }, \
     { F5, F0, B1, B7, D2 }, \
     { F6, F7, C7, D5, D3 }, \
@@ -54,7 +53,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define UNUSED_PINS
 
 /* COL2ROW, ROW2COL, or CUSTOM_MATRIX */
-#define DIODE_DIRECTION CUSTOM_MATRIX
+//#define DIODE_DIRECTION CUSTOM_MATRIX
 
 // #define BACKLIGHT_PIN B7
 // #define BACKLIGHT_BREATHING
diff --git a/keyboards/miniaxe/matrix.c b/keyboards/miniaxe/matrix.c
deleted file mode 100644
index 5fec1281df..0000000000
--- a/keyboards/miniaxe/matrix.c
+++ /dev/null
@@ -1,641 +0,0 @@
-/*
-Copyright 2012 Jun Wako <wakojun@gmail.com>
-
-This program is free software: you can redistribute it and/or modify
-it under the terms of the GNU General Public License as published by
-the Free Software Foundation, either version 2 of the License, or
-(at your option) any later version.
-
-This program is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-GNU General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with this program.  If not, see <http://www.gnu.org/licenses/>.
-*/
-
-/*
- * scan matrix
- */
-#include <stdint.h>
-#include <stdbool.h>
-#include <avr/io.h>
-#include "wait.h"
-#include "print.h"
-#include "debug.h"
-#include "util.h"
-#include "matrix.h"
-#include "split_util.h"
-#include "pro_micro.h"
-#include "config.h"
-#include "timer.h"
-#include "split_flags.h"
-
-#ifdef BACKLIGHT_ENABLE
-#   include "backlight.h"
-    extern backlight_config_t backlight_config;
-#endif
-
-#if defined(USE_I2C) || defined(EH)
-#  include "i2c.h"
-#else // USE_SERIAL
-#  include "serial.h"
-#endif
-
-#ifndef DEBOUNCING_DELAY
-#   define DEBOUNCING_DELAY 5
-#endif
-
-#if (DEBOUNCING_DELAY > 0)
-    static uint16_t debouncing_time;
-    static bool debouncing = false;
-#endif
-
-#if defined(USE_I2C) || defined(EH)
-
-#if (MATRIX_COLS <= 8)
-#    define print_matrix_header()  print("\nr/c 01234567\n")
-#    define print_matrix_row(row)  print_bin_reverse8(matrix_get_row(row))
-#    define matrix_bitpop(i)       bitpop(matrix[i])
-#    define ROW_SHIFTER ((uint8_t)1)
-#else
-#    error "Currently only supports 8 COLS"
-#endif
-
-#else // USE_SERIAL
-
-#if (MATRIX_COLS <= 8)
-#    define print_matrix_header()  print("\nr/c 01234567\n")
-#    define print_matrix_row(row)  print_bin_reverse8(matrix_get_row(row))
-#    define matrix_bitpop(i)       bitpop(matrix[i])
-#    define ROW_SHIFTER ((uint8_t)1)
-#elif (MATRIX_COLS <= 16)
-#    define print_matrix_header()  print("\nr/c 0123456789ABCDEF\n")
-#    define print_matrix_row(row)  print_bin_reverse16(matrix_get_row(row))
-#    define matrix_bitpop(i)       bitpop16(matrix[i])
-#    define ROW_SHIFTER ((uint16_t)1)
-#elif (MATRIX_COLS <= 32)
-#    define print_matrix_header()  print("\nr/c 0123456789ABCDEF0123456789ABCDEF\n")
-#    define print_matrix_row(row)  print_bin_reverse32(matrix_get_row(row))
-#    define matrix_bitpop(i)       bitpop32(matrix[i])
-#    define ROW_SHIFTER  ((uint32_t)1)
-#endif
-
-#endif
-static matrix_row_t matrix_debouncing[MATRIX_ROWS];
-
-#define ERROR_DISCONNECT_COUNT 5
-
-#define ROWS_PER_HAND (MATRIX_ROWS/2)
-
-static uint8_t error_count = 0;
-
-#if ((DIODE_DIRECTION == COL2ROW) || (DIODE_DIRECTION == ROW2COL))
-static uint8_t row_pins[MATRIX_ROWS] = MATRIX_ROW_PINS;
-static uint8_t col_pins[MATRIX_COLS] = MATRIX_COL_PINS;
-#elif (DIODE_DIRECTION == CUSTOM_MATRIX)
-static uint8_t row_col_pins[MATRIX_ROWS][MATRIX_COLS] = MATRIX_ROW_COL_PINS;
-#endif
-
-/* matrix state(1:on, 0:off) */
-static matrix_row_t matrix[MATRIX_ROWS];
-static matrix_row_t matrix_debouncing[MATRIX_ROWS];
-
-#if (DIODE_DIRECTION == COL2ROW)
-    static void init_cols(void);
-    static bool read_cols_on_row(matrix_row_t current_matrix[], uint8_t current_row);
-    static void unselect_rows(void);
-    static void select_row(uint8_t row);
-    static void unselect_row(uint8_t row);
-#elif (DIODE_DIRECTION == ROW2COL)
-    static void init_rows(void);
-    static bool read_rows_on_col(matrix_row_t current_matrix[], uint8_t current_col);
-    static void unselect_cols(void);
-    static void unselect_col(uint8_t col);
-    static void select_col(uint8_t col);
-#elif (DIODE_DIRECTION == CUSTOM_MATRIX)
-    static void init_cols_rows(void);
-    static bool read_cols(matrix_row_t current_matrix[], uint8_t current_row);
-#endif
-
-__attribute__ ((weak))
-void matrix_init_kb(void) {
-    matrix_init_user();
-}
-
-__attribute__ ((weak))
-void matrix_scan_kb(void) {
-    matrix_scan_user();
-}
-
-__attribute__ ((weak))
-void matrix_init_user(void) {
-}
-
-__attribute__ ((weak))
-void matrix_scan_user(void) {
-}
-
-__attribute__ ((weak))
-void matrix_slave_scan_user(void) {
-}
-
-inline
-uint8_t matrix_rows(void)
-{
-    return MATRIX_ROWS;
-}
-
-inline
-uint8_t matrix_cols(void)
-{
-    return MATRIX_COLS;
-}
-
-void matrix_init(void)
-{
-#ifdef DISABLE_JTAG
-  // JTAG disable for PORT F. write JTD bit twice within four cycles.
-  MCUCR |= (1<<JTD);
-  MCUCR |= (1<<JTD);
-#endif
-
-    debug_enable = true;
-    debug_matrix = true;
-    debug_mouse = true;
-
-    // Set pinout for right half if pinout for that half is defined
-    if (!isLeftHand) {
-#ifdef MATRIX_ROW_PINS_RIGHT
-        const uint8_t row_pins_right[MATRIX_ROWS] = MATRIX_ROW_PINS_RIGHT;
-        for (uint8_t i = 0; i < MATRIX_ROWS; i++)
-            row_pins[i] = row_pins_right[i];
-#endif
-#ifdef MATRIX_COL_PINS_RIGHT
-        const uint8_t col_pins_right[MATRIX_COLS] = MATRIX_COL_PINS_RIGHT;
-        for (uint8_t i = 0; i < MATRIX_COLS; i++)
-            col_pins[i] = col_pins_right[i];
-#endif
-    }
-
-    // initialize row and col
-#if (DIODE_DIRECTION == COL2ROW)
-    unselect_rows();
-    init_cols();
-#elif (DIODE_DIRECTION == ROW2COL)
-    unselect_cols();
-    init_rows();
-#elif (DIODE_DIRECTION == CUSTOM_MATRIX)
-    init_cols_rows();
-#endif
-
-    // initialize matrix state: all keys off
-    for (uint8_t i=0; i < MATRIX_ROWS; i++) {
-        matrix[i] = 0;
-        matrix_debouncing[i] = 0;
-    }
-    
-    matrix_init_quantum();
-    
-}
-
-uint8_t _matrix_scan(void)
-{
-    int offset = isLeftHand ? 0 : (ROWS_PER_HAND);
-#if (DIODE_DIRECTION == COL2ROW)
-    // Set row, read cols
-    for (uint8_t current_row = 0; current_row < ROWS_PER_HAND; current_row++) {
-#       if (DEBOUNCING_DELAY > 0)
-            bool matrix_changed = read_cols_on_row(matrix_debouncing+offset, current_row);
-
-            if (matrix_changed) {
-                debouncing = true;
-                debouncing_time = timer_read();
-            }
-
-#       else
-            read_cols_on_row(matrix+offset, current_row);
-#       endif
-
-    }
-
-#elif (DIODE_DIRECTION == ROW2COL)
-    // Set col, read rows
-    for (uint8_t current_col = 0; current_col < MATRIX_COLS; current_col++) {
-#       if (DEBOUNCING_DELAY > 0)
-            bool matrix_changed = read_rows_on_col(matrix_debouncing+offset, current_col);
-            if (matrix_changed) {
-                debouncing = true;
-                debouncing_time = timer_read();
-            }
-#       else
-             read_rows_on_col(matrix+offset, current_col);
-#       endif
-
-    }
-
-#elif (DIODE_DIRECTION == CUSTOM_MATRIX)
-    // Set row, read cols
-    for (uint8_t current_row = 0; current_row < ROWS_PER_HAND; current_row++) {
-#       if (DEBOUNCING_DELAY > 0)
-            bool matrix_changed = read_cols(matrix_debouncing+offset, current_row);
-            if (matrix_changed) {
-                debouncing = true;
-                debouncing_time = timer_read();
-            }
-#       else
-            read_cols(matrix+offset, current_row);
-#       endif
-    }
-#endif
-
-#   if (DEBOUNCING_DELAY > 0)
-        if (debouncing && (timer_elapsed(debouncing_time) > DEBOUNCING_DELAY)) {
-            for (uint8_t i = 0; i < ROWS_PER_HAND; i++) {
-                matrix[i+offset] = matrix_debouncing[i+offset];
-            }
-            debouncing = false;
-        }
-#   endif
-
-    return 1;
-}
-
-#if defined(USE_I2C) || defined(EH)
-
-// Get rows from other half over i2c
-int i2c_transaction(void) {
-    int slaveOffset = (isLeftHand) ? (ROWS_PER_HAND) : 0;
-    int err = 0;
-    
-    // write backlight info
-    #ifdef BACKLIGHT_ENABLE
-        if (BACKLIT_DIRTY) {
-            err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_WRITE);
-            if (err) goto i2c_error;
-            
-            // Backlight location
-            err = i2c_master_write(I2C_BACKLIT_START);
-            if (err) goto i2c_error;
-            
-            // Write backlight 
-            i2c_master_write(get_backlight_level());
-            
-            BACKLIT_DIRTY = false;
-        }
-    #endif
-
-    err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_WRITE);
-    if (err) goto i2c_error;
-
-    // start of matrix stored at I2C_KEYMAP_START
-    err = i2c_master_write(I2C_KEYMAP_START);
-    if (err) goto i2c_error;
-
-    // Start read
-    err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_READ);
-    if (err) goto i2c_error;
-
-    if (!err) {
-        int i;
-        for (i = 0; i < ROWS_PER_HAND-1; ++i) {
-            matrix[slaveOffset+i] = i2c_master_read(I2C_ACK);
-        }
-        matrix[slaveOffset+i] = i2c_master_read(I2C_NACK);
-        i2c_master_stop();
-    } else {
-i2c_error: // the cable is disconnceted, or something else went wrong
-        i2c_reset_state();
-        return err;
-    }
-    
-    #ifdef RGBLIGHT_ENABLE
-        if (RGB_DIRTY) {
-            err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_WRITE);
-            if (err) goto i2c_error;
-            
-            // RGB Location
-            err = i2c_master_write(I2C_RGB_START);
-            if (err) goto i2c_error;
-            
-            uint32_t dword = eeconfig_read_rgblight();
-            
-            // Write RGB
-            err = i2c_master_write_data(&dword, 4);
-            if (err) goto i2c_error;
-            
-            RGB_DIRTY = false;
-            i2c_master_stop();
-        }
-    #endif
-
-    return 0;
-}
-
-#else // USE_SERIAL
-
-
-typedef struct _Serial_s2m_buffer_t {
-    // TODO: if MATRIX_COLS > 8 change to uint8_t packed_matrix[] for pack/unpack
-    matrix_row_t smatrix[ROWS_PER_HAND];
-} Serial_s2m_buffer_t;
-
-volatile Serial_s2m_buffer_t serial_s2m_buffer = {};
-volatile Serial_m2s_buffer_t serial_m2s_buffer = {};
-uint8_t volatile status0 = 0;
-
-SSTD_t transactions[] = {
-    { (uint8_t *)&status0,
-      sizeof(serial_m2s_buffer), (uint8_t *)&serial_m2s_buffer,
-      sizeof(serial_s2m_buffer), (uint8_t *)&serial_s2m_buffer
-  }
-};
-
-void serial_master_init(void)
-{ soft_serial_initiator_init(transactions, TID_LIMIT(transactions)); }
-
-void serial_slave_init(void)
-{ soft_serial_target_init(transactions, TID_LIMIT(transactions)); }
-
-int serial_transaction(void) {
-    int slaveOffset = (isLeftHand) ? (ROWS_PER_HAND) : 0;
-
-    if (soft_serial_transaction()) {
-        return 1;
-    }
-
-    // TODO:  if MATRIX_COLS > 8 change to unpack()
-    for (int i = 0; i < ROWS_PER_HAND; ++i) {
-        matrix[slaveOffset+i] = serial_s2m_buffer.smatrix[i];
-    }
-    
-    #ifdef RGBLIGHT_ENABLE
-        // Code to send RGB over serial goes here (not implemented yet)
-    #endif
-    
-    #ifdef BACKLIGHT_ENABLE
-        // Write backlight level for slave to read
-        serial_m2s_buffer.backlight_level = backlight_config.enable ? backlight_config.level : 0;
-    #endif
-
-    return 0;
-}
-#endif
-
-uint8_t matrix_scan(void)
-{
-    uint8_t ret = _matrix_scan();
-
-#if defined(USE_I2C) || defined(EH)
-    if( i2c_transaction() ) {
-#else // USE_SERIAL
-    if( serial_transaction() ) {
-#endif
-
-        error_count++;
-
-        if (error_count > ERROR_DISCONNECT_COUNT) {
-            // reset other half if disconnected
-            int slaveOffset = (isLeftHand) ? (ROWS_PER_HAND) : 0;
-            for (int i = 0; i < ROWS_PER_HAND; ++i) {
-                matrix[slaveOffset+i] = 0;
-            }
-        }
-    } else {
-        error_count = 0;
-    }
-    matrix_scan_quantum();
-    return ret;
-}
-
-void matrix_slave_scan(void) {
-    _matrix_scan();
-
-    int offset = (isLeftHand) ? 0 : ROWS_PER_HAND;
-
-#if defined(USE_I2C) || defined(EH)
-    for (int i = 0; i < ROWS_PER_HAND; ++i) {
-        i2c_slave_buffer[I2C_KEYMAP_START+i] = matrix[offset+i];
-    }   
-#else // USE_SERIAL
-    // TODO: if MATRIX_COLS > 8 change to pack()
-    for (int i = 0; i < ROWS_PER_HAND; ++i) {
-        serial_s2m_buffer.smatrix[i] = matrix[offset+i];
-    }
-#endif
-    matrix_slave_scan_user();
-}
-
-bool matrix_is_modified(void)
-{
-    if (debouncing) return false;
-    return true;
-}
-
-inline
-bool matrix_is_on(uint8_t row, uint8_t col)
-{
-    return (matrix[row] & ((matrix_row_t)1<<col));
-}
-
-inline
-matrix_row_t matrix_get_row(uint8_t row)
-{
-    return matrix[row];
-}
-
-void matrix_print(void)
-{
-    print("\nr/c 0123456789ABCDEF\n");
-    for (uint8_t row = 0; row < MATRIX_ROWS; row++) {
-        phex(row); print(": ");
-        pbin_reverse16(matrix_get_row(row));
-        print("\n");
-    }
-}
-
-uint8_t matrix_key_count(void)
-{
-    uint8_t count = 0;
-    for (uint8_t i = 0; i < MATRIX_ROWS; i++) {
-        count += bitpop16(matrix[i]);
-    }
-    return count;
-}
-
-#if (DIODE_DIRECTION == COL2ROW)
-
-static void init_cols(void)
-{
-    for(uint8_t x = 0; x < MATRIX_COLS; x++) {
-        uint8_t pin = col_pins[x];
-        _SFR_IO8((pin >> 4) + 1) &= ~_BV(pin & 0xF); // IN
-        _SFR_IO8((pin >> 4) + 2) |=  _BV(pin & 0xF); // HI
-    }
-}
-
-static bool read_cols_on_row(matrix_row_t current_matrix[], uint8_t current_row)
-{
-    // Store last value of row prior to reading
-    matrix_row_t last_row_value = current_matrix[current_row];
-
-    // Clear data in matrix row
-    current_matrix[current_row] = 0;
-
-    // Select row and wait for row selecton to stabilize
-    select_row(current_row);
-    wait_us(30);
-
-    // For each col...
-    for(uint8_t col_index = 0; col_index < MATRIX_COLS; col_index++) {
-
-        // Select the col pin to read (active low)
-        uint8_t pin = col_pins[col_index];
-        uint8_t pin_state = (_SFR_IO8(pin >> 4) & _BV(pin & 0xF));
-
-        // Populate the matrix row with the state of the col pin
-        current_matrix[current_row] |=  pin_state ? 0 : (ROW_SHIFTER << col_index);
-    }
-
-    // Unselect row
-    unselect_row(current_row);
-
-    return (last_row_value != current_matrix[current_row]);
-}
-
-static void select_row(uint8_t row)
-{
-    uint8_t pin = row_pins[row];
-    _SFR_IO8((pin >> 4) + 1) |=  _BV(pin & 0xF); // OUT
-    _SFR_IO8((pin >> 4) + 2) &= ~_BV(pin & 0xF); // LOW
-}
-
-static void unselect_row(uint8_t row)
-{
-    uint8_t pin = row_pins[row];
-    _SFR_IO8((pin >> 4) + 1) &= ~_BV(pin & 0xF); // IN
-    _SFR_IO8((pin >> 4) + 2) |=  _BV(pin & 0xF); // HI
-}
-
-static void unselect_rows(void)
-{
-    for(uint8_t x = 0; x < ROWS_PER_HAND; x++) {
-        uint8_t pin = row_pins[x];
-        _SFR_IO8((pin >> 4) + 1) &= ~_BV(pin & 0xF); // IN
-        _SFR_IO8((pin >> 4) + 2) |=  _BV(pin & 0xF); // HI
-    }
-}
-
-#elif (DIODE_DIRECTION == ROW2COL)
-
-static void init_rows(void)
-{
-    for(uint8_t x = 0; x < ROWS_PER_HAND; x++) {
-        uint8_t pin = row_pins[x];
-        _SFR_IO8((pin >> 4) + 1) &= ~_BV(pin & 0xF); // IN
-        _SFR_IO8((pin >> 4) + 2) |=  _BV(pin & 0xF); // HI
-    }
-}
-
-static bool read_rows_on_col(matrix_row_t current_matrix[], uint8_t current_col)
-{
-    bool matrix_changed = false;
-
-    // Select col and wait for col selecton to stabilize
-    select_col(current_col);
-    wait_us(30);
-
-    // For each row...
-    for(uint8_t row_index = 0; row_index < ROWS_PER_HAND; row_index++)
-    {
-
-        // Store last value of row prior to reading
-        matrix_row_t last_row_value = current_matrix[row_index];
-
-        // Check row pin state
-        if ((_SFR_IO8(row_pins[row_index] >> 4) & _BV(row_pins[row_index] & 0xF)) == 0)
-        {
-            // Pin LO, set col bit
-            current_matrix[row_index] |= (ROW_SHIFTER << current_col);
-        }
-        else
-        {
-            // Pin HI, clear col bit
-            current_matrix[row_index] &= ~(ROW_SHIFTER << current_col);
-        }
-
-        // Determine if the matrix changed state
-        if ((last_row_value != current_matrix[row_index]) && !(matrix_changed))
-        {
-            matrix_changed = true;
-        }
-    }
-
-    // Unselect col
-    unselect_col(current_col);
-
-    return matrix_changed;
-}
-
-static void select_col(uint8_t col)
-{
-    uint8_t pin = col_pins[col];
-    _SFR_IO8((pin >> 4) + 1) |=  _BV(pin & 0xF); // OUT
-    _SFR_IO8((pin >> 4) + 2) &= ~_BV(pin & 0xF); // LOW
-}
-
-static void unselect_col(uint8_t col)
-{
-    uint8_t pin = col_pins[col];
-    _SFR_IO8((pin >> 4) + 1) &= ~_BV(pin & 0xF); // IN
-    _SFR_IO8((pin >> 4) + 2) |=  _BV(pin & 0xF); // HI
-}
-
-static void unselect_cols(void)
-{
-    for(uint8_t x = 0; x < MATRIX_COLS; x++) {
-        uint8_t pin = col_pins[x];
-        _SFR_IO8((pin >> 4) + 1) &= ~_BV(pin & 0xF); // IN
-        _SFR_IO8((pin >> 4) + 2) |=  _BV(pin & 0xF); // HI
-    }
-}
-
-#elif (DIODE_DIRECTION == CUSTOM_MATRIX)
-
-static void init_cols_rows(void)
-{
-    for(int row = 0; row < MATRIX_ROWS; row++) {
-        for(int col = 0; col < MATRIX_COLS; col++) {
-            uint8_t pin = row_col_pins[row][col];
-            if(pin == NO_PIN) {
-                continue;
-            }
-            // DDxn set 0 for input
-            _SFR_IO8((pin >> 4) + 1) &=  ~_BV(pin & 0xF);
-            // PORTxn set 1 for input/pullup
-            _SFR_IO8((pin >> 4) + 2) |= _BV(pin & 0xF);
-        }
-    }
-}
-
-static bool read_cols(matrix_row_t current_matrix[], uint8_t current_row)
-{
-    matrix_row_t last_row_value = current_matrix[current_row];
-    current_matrix[current_row] = 0;
-
-    for(uint8_t col_index = 0; col_index < MATRIX_COLS; col_index++) {
-        uint8_t pin = row_col_pins[current_row][col_index];
-        if(pin == NO_PIN) {
-            current_matrix[current_row] |= 0;
-        }
-        else {
-            uint8_t pin_state = (_SFR_IO8(pin >> 4) & _BV(pin & 0xF));
-            current_matrix[current_row] |= pin_state ? 0 : (ROW_SHIFTER << col_index);
-        }
-    }
-
-    return (last_row_value != current_matrix[current_row]);
-}
-
-#endif
diff --git a/keyboards/miniaxe/rules.mk b/keyboards/miniaxe/rules.mk
index 96e27686b8..2f56a907ba 100644
--- a/keyboards/miniaxe/rules.mk
+++ b/keyboards/miniaxe/rules.mk
@@ -1,4 +1,3 @@
-SRC += matrix.c
 
 # MCU name
 #MCU = at90usb1286
@@ -83,6 +82,6 @@ FAUXCLICKY_ENABLE = no      # Use buzzer to emulate clicky switches
 HD44780_ENABLE = no 		# Enable support for HD44780 based LCDs (+400)
 
 DEBUG_ENABLE = no
-CUSTOM_MATRIX = yes         # Use custom matrix code 
+CUSTOM_MATRIX = no         # Use custom matrix code
 SPLIT_KEYBOARD = yes        # Use shared split_common code
 
diff --git a/quantum/config_common.h b/quantum/config_common.h
index 606cd9381a..0b2e408a43 100644
--- a/quantum/config_common.h
+++ b/quantum/config_common.h
@@ -21,6 +21,9 @@
 #define ROW2COL       1
 #define CUSTOM_MATRIX 2 /* Disables built-in matrix scanning code */
 
+// useful for direct pin mapping
+#define NO_PIN (~0)
+
 #ifdef __AVR__
     #ifndef __ASSEMBLER__
       #include <avr/io.h>
diff --git a/quantum/debounce.c b/quantum/debounce.c
new file mode 100644
index 0000000000..929023ab2d
--- /dev/null
+++ b/quantum/debounce.c
@@ -0,0 +1,52 @@
+
+#include "matrix.h"
+#include "timer.h"
+#include "quantum.h"
+
+#ifndef DEBOUNCING_DELAY
+#  define DEBOUNCING_DELAY 5
+#endif
+
+void debounce_init(uint8_t num_rows) {
+}
+
+#if DEBOUNCING_DELAY > 0
+
+static bool debouncing = false;
+
+void debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed) {
+  static uint16_t debouncing_time;
+
+  if (changed) {
+    debouncing = true;
+    debouncing_time = timer_read();
+  }
+
+  if (debouncing && (timer_elapsed(debouncing_time) > DEBOUNCING_DELAY)) {
+    for (uint8_t i = 0; i < num_rows; i++) {
+      cooked[i] = raw[i];
+    }
+    debouncing = false;
+  }
+}
+
+bool debounce_active(void) {
+  return debouncing;
+}
+
+#else
+
+// no debounce
+void debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed) {
+  if (changed)
+  {
+  for (uint8_t i = 0; i < num_rows; i++) {
+      cooked[i] = raw[i];
+    }
+  }
+}
+
+bool debounce_active(void) {
+  return false;
+}
+#endif
diff --git a/quantum/debounce.h b/quantum/debounce.h
new file mode 100644
index 0000000000..360af77e78
--- /dev/null
+++ b/quantum/debounce.h
@@ -0,0 +1,11 @@
+#pragma once
+
+// raw is the current key state
+// on entry cooked is the previous debounced state
+// on exit cooked is the current debounced state
+// changed is true if raw has changed since the last call
+void debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed);
+
+bool debounce_active(void);
+
+void debounce_init(uint8_t num_rows);
\ No newline at end of file
diff --git a/quantum/matrix.c b/quantum/matrix.c
index 9b5ce33d23..49a1845696 100644
--- a/quantum/matrix.c
+++ b/quantum/matrix.c
@@ -21,21 +21,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "debug.h"
 #include "util.h"
 #include "matrix.h"
-#include "timer.h"
+#include "debounce.h"
 #include "quantum.h"
 
-
-/* Set 0 if debouncing isn't needed */
-
-#ifndef DEBOUNCING_DELAY
-#   define DEBOUNCING_DELAY 5
-#endif
-
-#if (DEBOUNCING_DELAY > 0)
-    static uint16_t debouncing_time;
-    static bool debouncing = false;
-#endif
-
 #if (MATRIX_COLS <= 8)
 #    define print_matrix_header()  print("\nr/c 01234567\n")
 #    define print_matrix_row(row)  print_bin_reverse8(matrix_get_row(row))
@@ -63,9 +51,9 @@ static const pin_t col_pins[MATRIX_COLS] = MATRIX_COL_PINS;
 #endif
 
 /* matrix state(1:on, 0:off) */
-static matrix_row_t matrix[MATRIX_ROWS];
+static matrix_row_t raw_matrix[MATRIX_ROWS];
 
-static matrix_row_t matrix_debouncing[MATRIX_ROWS];
+static matrix_row_t matrix[MATRIX_ROWS];
 
 
 #if (DIODE_DIRECTION == COL2ROW)
@@ -157,70 +145,39 @@ void matrix_init(void) {
 
     // initialize matrix state: all keys off
     for (uint8_t i=0; i < MATRIX_ROWS; i++) {
+        raw_matrix[i] = 0;
         matrix[i] = 0;
-        matrix_debouncing[i] = 0;
     }
+    debounce_init(MATRIX_ROWS);
 
     matrix_init_quantum();
 }
 
 uint8_t matrix_scan(void)
 {
+  bool changed = false;
 
 #if (DIODE_DIRECTION == COL2ROW)
-
-    // Set row, read cols
-    for (uint8_t current_row = 0; current_row < MATRIX_ROWS; current_row++) {
-#       if (DEBOUNCING_DELAY > 0)
-            bool matrix_changed = read_cols_on_row(matrix_debouncing, current_row);
-
-            if (matrix_changed) {
-                debouncing = true;
-                debouncing_time = timer_read();
-            }
-
-#       else
-            read_cols_on_row(matrix, current_row);
-#       endif
-
-    }
-
+  // Set row, read cols
+  for (uint8_t current_row = 0; current_row < MATRIX_ROWS; current_row++) {
+    changed |= read_cols_on_row(raw_matrix, current_row);
+  }
 #elif (DIODE_DIRECTION == ROW2COL)
-
-    // Set col, read rows
-    for (uint8_t current_col = 0; current_col < MATRIX_COLS; current_col++) {
-#       if (DEBOUNCING_DELAY > 0)
-            bool matrix_changed = read_rows_on_col(matrix_debouncing, current_col);
-            if (matrix_changed) {
-                debouncing = true;
-                debouncing_time = timer_read();
-            }
-#       else
-             read_rows_on_col(matrix, current_col);
-#       endif
-
-    }
-
+  // Set col, read rows
+  for (uint8_t current_col = 0; current_col < MATRIX_COLS; current_col++) {
+    changed |= read_rows_on_col(raw_matrix, current_col);
+  }
 #endif
 
-#   if (DEBOUNCING_DELAY > 0)
-        if (debouncing && (timer_elapsed(debouncing_time) > DEBOUNCING_DELAY)) {
-            for (uint8_t i = 0; i < MATRIX_ROWS; i++) {
-                matrix[i] = matrix_debouncing[i];
-            }
-            debouncing = false;
-        }
-#   endif
+  debounce(raw_matrix, matrix, MATRIX_ROWS, changed);
 
-    matrix_scan_quantum();
-    return 1;
+  matrix_scan_quantum();
+  return 1;
 }
 
 bool matrix_is_modified(void)
 {
-#if (DEBOUNCING_DELAY > 0)
-    if (debouncing) return false;
-#endif
+    if (debounce_active()) return false;
     return true;
 }
 
diff --git a/quantum/split_common/i2c.h b/quantum/split_common/i2c.h
index b3cbe8c826..91e8e96f47 100644
--- a/quantum/split_common/i2c.h
+++ b/quantum/split_common/i2c.h
@@ -1,5 +1,4 @@
-#ifndef I2C_H
-#define I2C_H
+#pragma once
 
 #include <stdint.h>
 
@@ -58,5 +57,3 @@ extern unsigned char i2c_readNak(void);
 extern unsigned char i2c_read(unsigned char ack);
 
 #define i2c_read(ack)  (ack) ? i2c_readAck() : i2c_readNak();
-
-#endif
diff --git a/quantum/split_common/matrix.c b/quantum/split_common/matrix.c
index 2c37053f88..c3d2857ed5 100644
--- a/quantum/split_common/matrix.c
+++ b/quantum/split_common/matrix.c
@@ -25,529 +25,304 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "matrix.h"
 #include "split_util.h"
 #include "config.h"
-#include "timer.h"
 #include "split_flags.h"
 #include "quantum.h"
-
-#ifdef BACKLIGHT_ENABLE
-#   include "backlight.h"
-    extern backlight_config_t backlight_config;
-#endif
-
-#if defined(USE_I2C) || defined(EH)
-#  include "i2c.h"
-#else // USE_SERIAL
-#  include "serial.h"
-#endif
-
-#ifndef DEBOUNCING_DELAY
-#   define DEBOUNCING_DELAY 5
-#endif
-
-#if (DEBOUNCING_DELAY > 0)
-    static uint16_t debouncing_time;
-    static bool debouncing = false;
-#endif
-
-#if defined(USE_I2C) || defined(EH)
-
-#if (MATRIX_COLS <= 8)
-#    define print_matrix_header()  print("\nr/c 01234567\n")
-#    define print_matrix_row(row)  print_bin_reverse8(matrix_get_row(row))
-#    define matrix_bitpop(i)       bitpop(matrix[i])
-#    define ROW_SHIFTER ((uint8_t)1)
-#else
-#    error "Currently only supports 8 COLS"
-#endif
-
-#else // USE_SERIAL
+#include "debounce.h"
+#include "transport.h"
 
 #if (MATRIX_COLS <= 8)
-#    define print_matrix_header()  print("\nr/c 01234567\n")
-#    define print_matrix_row(row)  print_bin_reverse8(matrix_get_row(row))
-#    define matrix_bitpop(i)       bitpop(matrix[i])
-#    define ROW_SHIFTER ((uint8_t)1)
+#  define print_matrix_header() print("\nr/c 01234567\n")
+#  define print_matrix_row(row) print_bin_reverse8(matrix_get_row(row))
+#  define matrix_bitpop(i) bitpop(matrix[i])
+#  define ROW_SHIFTER ((uint8_t)1)
 #elif (MATRIX_COLS <= 16)
-#    define print_matrix_header()  print("\nr/c 0123456789ABCDEF\n")
-#    define print_matrix_row(row)  print_bin_reverse16(matrix_get_row(row))
-#    define matrix_bitpop(i)       bitpop16(matrix[i])
-#    define ROW_SHIFTER ((uint16_t)1)
+#  define print_matrix_header() print("\nr/c 0123456789ABCDEF\n")
+#  define print_matrix_row(row) print_bin_reverse16(matrix_get_row(row))
+#  define matrix_bitpop(i) bitpop16(matrix[i])
+#  define ROW_SHIFTER ((uint16_t)1)
 #elif (MATRIX_COLS <= 32)
-#    define print_matrix_header()  print("\nr/c 0123456789ABCDEF0123456789ABCDEF\n")
-#    define print_matrix_row(row)  print_bin_reverse32(matrix_get_row(row))
-#    define matrix_bitpop(i)       bitpop32(matrix[i])
-#    define ROW_SHIFTER  ((uint32_t)1)
-#endif
-
+#  define print_matrix_header() print("\nr/c 0123456789ABCDEF0123456789ABCDEF\n")
+#  define print_matrix_row(row) print_bin_reverse32(matrix_get_row(row))
+#  define matrix_bitpop(i) bitpop32(matrix[i])
+#  define ROW_SHIFTER ((uint32_t)1)
 #endif
-static matrix_row_t matrix_debouncing[MATRIX_ROWS];
 
 #define ERROR_DISCONNECT_COUNT 5
 
-#define ROWS_PER_HAND (MATRIX_ROWS/2)
-
-static uint8_t error_count = 0;
+#define ROWS_PER_HAND (MATRIX_ROWS / 2)
 
+#ifdef DIRECT_PINS
+static pin_t direct_pins[MATRIX_ROWS][MATRIX_COLS] = DIRECT_PINS;
+#else
 static pin_t row_pins[MATRIX_ROWS] = MATRIX_ROW_PINS;
 static pin_t col_pins[MATRIX_COLS] = MATRIX_COL_PINS;
+#endif
 
 /* matrix state(1:on, 0:off) */
 static matrix_row_t matrix[MATRIX_ROWS];
-static matrix_row_t matrix_debouncing[MATRIX_ROWS];
-
-#if (DIODE_DIRECTION == COL2ROW)
-    static void init_cols(void);
-    static bool read_cols_on_row(matrix_row_t current_matrix[], uint8_t current_row);
-    static void unselect_rows(void);
-    static void select_row(uint8_t row);
-    static void unselect_row(uint8_t row);
-#elif (DIODE_DIRECTION == ROW2COL)
-    static void init_rows(void);
-    static bool read_rows_on_col(matrix_row_t current_matrix[], uint8_t current_col);
-    static void unselect_cols(void);
-    static void unselect_col(uint8_t col);
-    static void select_col(uint8_t col);
-#endif
+static matrix_row_t raw_matrix[ROWS_PER_HAND];
 
-__attribute__ ((weak))
-void matrix_init_kb(void) {
-    matrix_init_user();
-}
+// row offsets for each hand
+uint8_t thisHand, thatHand;
 
-__attribute__ ((weak))
-void matrix_scan_kb(void) {
-    matrix_scan_user();
-}
+// user-defined overridable functions
 
-__attribute__ ((weak))
-void matrix_init_user(void) {
-}
+__attribute__((weak)) void matrix_init_kb(void) { matrix_init_user(); }
 
-__attribute__ ((weak))
-void matrix_scan_user(void) {
-}
+__attribute__((weak)) void matrix_scan_kb(void) { matrix_scan_user(); }
 
-__attribute__ ((weak))
-void matrix_slave_scan_user(void) {
-}
+__attribute__((weak)) void matrix_init_user(void) {}
 
-inline
-uint8_t matrix_rows(void)
-{
-    return MATRIX_ROWS;
-}
+__attribute__((weak)) void matrix_scan_user(void) {}
 
-inline
-uint8_t matrix_cols(void)
-{
-    return MATRIX_COLS;
-}
+__attribute__((weak)) void matrix_slave_scan_user(void) {}
 
-void matrix_init(void)
-{
-    debug_enable = true;
-    debug_matrix = true;
-    debug_mouse = true;
+// helper functions
 
-    // Set pinout for right half if pinout for that half is defined
-    if (!isLeftHand) {
-#ifdef MATRIX_ROW_PINS_RIGHT
-        const uint8_t row_pins_right[MATRIX_ROWS] = MATRIX_ROW_PINS_RIGHT;
-        for (uint8_t i = 0; i < MATRIX_ROWS; i++)
-            row_pins[i] = row_pins_right[i];
-#endif
-#ifdef MATRIX_COL_PINS_RIGHT
-        const uint8_t col_pins_right[MATRIX_COLS] = MATRIX_COL_PINS_RIGHT;
-        for (uint8_t i = 0; i < MATRIX_COLS; i++)
-            col_pins[i] = col_pins_right[i];
-#endif
-    }
+inline uint8_t matrix_rows(void) { return MATRIX_ROWS; }
 
-    // initialize row and col
-#if (DIODE_DIRECTION == COL2ROW)
-    unselect_rows();
-    init_cols();
-#elif (DIODE_DIRECTION == ROW2COL)
-    unselect_cols();
-    init_rows();
-#endif
+inline uint8_t matrix_cols(void) { return MATRIX_COLS; }
 
-    // initialize matrix state: all keys off
-    for (uint8_t i=0; i < MATRIX_ROWS; i++) {
-        matrix[i] = 0;
-        matrix_debouncing[i] = 0;
-    }
-    
-    matrix_init_quantum();
-    
+bool matrix_is_modified(void) {
+  if (debounce_active()) return false;
+  return true;
 }
 
-uint8_t _matrix_scan(void)
-{
-    int offset = isLeftHand ? 0 : (ROWS_PER_HAND);
-#if (DIODE_DIRECTION == COL2ROW)
-    // Set row, read cols
-    for (uint8_t current_row = 0; current_row < ROWS_PER_HAND; current_row++) {
-#       if (DEBOUNCING_DELAY > 0)
-            bool matrix_changed = read_cols_on_row(matrix_debouncing+offset, current_row);
-
-            if (matrix_changed) {
-                debouncing = true;
-                debouncing_time = timer_read();
-            }
-
-#       else
-            read_cols_on_row(matrix+offset, current_row);
-#       endif
-
-    }
+inline bool matrix_is_on(uint8_t row, uint8_t col) { return (matrix[row] & ((matrix_row_t)1 << col)); }
 
-#elif (DIODE_DIRECTION == ROW2COL)
-    // Set col, read rows
-    for (uint8_t current_col = 0; current_col < MATRIX_COLS; current_col++) {
-#       if (DEBOUNCING_DELAY > 0)
-            bool matrix_changed = read_rows_on_col(matrix_debouncing+offset, current_col);
-            if (matrix_changed) {
-                debouncing = true;
-                debouncing_time = timer_read();
-            }
-#       else
-             read_rows_on_col(matrix+offset, current_col);
-#       endif
+inline matrix_row_t matrix_get_row(uint8_t row) { return matrix[row]; }
 
-    }
-#endif
+void matrix_print(void) {
+  print_matrix_header();
 
-#   if (DEBOUNCING_DELAY > 0)
-        if (debouncing && (timer_elapsed(debouncing_time) > DEBOUNCING_DELAY)) {
-            for (uint8_t i = 0; i < ROWS_PER_HAND; i++) {
-                matrix[i+offset] = matrix_debouncing[i+offset];
-            }
-            debouncing = false;
-        }
-#   endif
+  for (uint8_t row = 0; row < MATRIX_ROWS; row++) {
+    phex(row);
+    print(": ");
+    print_matrix_row(row);
+    print("\n");
+  }
+}
 
-    return 1;
+uint8_t matrix_key_count(void) {
+  uint8_t count = 0;
+  for (uint8_t i = 0; i < MATRIX_ROWS; i++) {
+    count += matrix_bitpop(i);
+  }
+  return count;
 }
 
-#if defined(USE_I2C) || defined(EH)
-
-// Get rows from other half over i2c
-int i2c_transaction(void) {
-    int slaveOffset = (isLeftHand) ? (ROWS_PER_HAND) : 0;
-    int err = 0;
-    
-    // write backlight info
-    #ifdef BACKLIGHT_ENABLE
-        if (BACKLIT_DIRTY) {
-            err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_WRITE);
-            if (err) goto i2c_error;
-            
-            // Backlight location
-            err = i2c_master_write(I2C_BACKLIT_START);
-            if (err) goto i2c_error;
-            
-            // Write backlight 
-            i2c_master_write(get_backlight_level());
-            
-            BACKLIT_DIRTY = false;
-        }
-    #endif
+// matrix code
 
-    err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_WRITE);
-    if (err) goto i2c_error;
+#ifdef DIRECT_PINS
 
-    // start of matrix stored at I2C_KEYMAP_START
-    err = i2c_master_write(I2C_KEYMAP_START);
-    if (err) goto i2c_error;
+static void init_pins(void) {
+  for (int row = 0; row < MATRIX_ROWS; row++) {
+    for (int col = 0; col < MATRIX_COLS; col++) {
+      pin_t pin = direct_pins[row][col];
+      if (pin != NO_PIN) {
+        setPinInputHigh(pin);
+      }
+    }
+  }
+}
 
-    // Start read
-    err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_READ);
-    if (err) goto i2c_error;
+static bool read_cols_on_row(matrix_row_t current_matrix[], uint8_t current_row) {
+  matrix_row_t last_row_value = current_matrix[current_row];
+  current_matrix[current_row] = 0;
 
-    if (!err) {
-        int i;
-        for (i = 0; i < ROWS_PER_HAND-1; ++i) {
-            matrix[slaveOffset+i] = i2c_master_read(I2C_ACK);
-        }
-        matrix[slaveOffset+i] = i2c_master_read(I2C_NACK);
-        i2c_master_stop();
-    } else {
-i2c_error: // the cable is disconnceted, or something else went wrong
-        i2c_reset_state();
-        return err;
+  for (uint8_t col_index = 0; col_index < MATRIX_COLS; col_index++) {
+    pin_t pin = direct_pins[current_row][col_index];
+    if (pin != NO_PIN) {
+      current_matrix[current_row] |= readPin(pin) ? 0 : (ROW_SHIFTER << col_index);
     }
-    
-    #ifdef RGBLIGHT_ENABLE
-        if (RGB_DIRTY) {
-            err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_WRITE);
-            if (err) goto i2c_error;
-            
-            // RGB Location
-            err = i2c_master_write(I2C_RGB_START);
-            if (err) goto i2c_error;
-            
-            uint32_t dword = eeconfig_read_rgblight();
-            
-            // Write RGB
-            err = i2c_master_write_data(&dword, 4);
-            if (err) goto i2c_error;
-            
-            RGB_DIRTY = false;
-            i2c_master_stop();
-        }
-    #endif
+  }
 
-    return 0;
+  return (last_row_value != current_matrix[current_row]);
 }
 
-#else // USE_SERIAL
-
+#elif (DIODE_DIRECTION == COL2ROW)
 
-typedef struct _Serial_s2m_buffer_t {
-    // TODO: if MATRIX_COLS > 8 change to uint8_t packed_matrix[] for pack/unpack
-    matrix_row_t smatrix[ROWS_PER_HAND];
-} Serial_s2m_buffer_t;
+static void select_row(uint8_t row) {
+  writePinLow(row_pins[row]);
+  setPinOutput(row_pins[row]);
+}
 
-volatile Serial_s2m_buffer_t serial_s2m_buffer = {};
-volatile Serial_m2s_buffer_t serial_m2s_buffer = {};
-uint8_t volatile status0 = 0;
+static void unselect_row(uint8_t row) { setPinInputHigh(row_pins[row]); }
 
-SSTD_t transactions[] = {
-    { (uint8_t *)&status0,
-      sizeof(serial_m2s_buffer), (uint8_t *)&serial_m2s_buffer,
-      sizeof(serial_s2m_buffer), (uint8_t *)&serial_s2m_buffer
+static void unselect_rows(void) {
+  for (uint8_t x = 0; x < ROWS_PER_HAND; x++) {
+    setPinInputHigh(row_pins[x]);
   }
-};
+}
 
-void serial_master_init(void)
-{ soft_serial_initiator_init(transactions, TID_LIMIT(transactions)); }
+static void init_pins(void) {
+  unselect_rows();
+  for (uint8_t x = 0; x < MATRIX_COLS; x++) {
+    setPinInputHigh(col_pins[x]);
+  }
+}
 
-void serial_slave_init(void)
-{ soft_serial_target_init(transactions, TID_LIMIT(transactions)); }
+static bool read_cols_on_row(matrix_row_t current_matrix[], uint8_t current_row) {
+  // Store last value of row prior to reading
+  matrix_row_t last_row_value = current_matrix[current_row];
 
-int serial_transaction(void) {
-    int slaveOffset = (isLeftHand) ? (ROWS_PER_HAND) : 0;
+  // Clear data in matrix row
+  current_matrix[current_row] = 0;
 
-    if (soft_serial_transaction()) {
-        return 1;
-    }
+  // Select row and wait for row selecton to stabilize
+  select_row(current_row);
+  wait_us(30);
 
-    // TODO:  if MATRIX_COLS > 8 change to unpack()
-    for (int i = 0; i < ROWS_PER_HAND; ++i) {
-        matrix[slaveOffset+i] = serial_s2m_buffer.smatrix[i];
-    }
-    
-    #if defined(RGBLIGHT_ENABLE) && defined(RGBLIGHT_SPLIT)
-        // Code to send RGB over serial goes here (not implemented yet)
-    #endif
-    
-    #ifdef BACKLIGHT_ENABLE
-        // Write backlight level for slave to read
-        serial_m2s_buffer.backlight_level = backlight_config.enable ? backlight_config.level : 0;
-    #endif
-
-    return 0;
-}
-#endif
+  // For each col...
+  for (uint8_t col_index = 0; col_index < MATRIX_COLS; col_index++) {
+    // Populate the matrix row with the state of the col pin
+    current_matrix[current_row] |= readPin(col_pins[col_index]) ? 0 : (ROW_SHIFTER << col_index);
+  }
 
-uint8_t matrix_scan(void)
-{
-    uint8_t ret = _matrix_scan();
+  // Unselect row
+  unselect_row(current_row);
 
-#if defined(USE_I2C) || defined(EH)
-    if( i2c_transaction() ) {
-#else // USE_SERIAL
-    if( serial_transaction() ) {
-#endif
+  return (last_row_value != current_matrix[current_row]);
+}
 
-        error_count++;
+#elif (DIODE_DIRECTION == ROW2COL)
 
-        if (error_count > ERROR_DISCONNECT_COUNT) {
-            // reset other half if disconnected
-            int slaveOffset = (isLeftHand) ? (ROWS_PER_HAND) : 0;
-            for (int i = 0; i < ROWS_PER_HAND; ++i) {
-                matrix[slaveOffset+i] = 0;
-            }
-        }
-    } else {
-        error_count = 0;
-    }
-    matrix_scan_quantum();
-    return ret;
+static void select_col(uint8_t col) {
+  writePinLow(col_pins[col]);
+  setPinOutput(col_pins[col]);
 }
 
-void matrix_slave_scan(void) {
-    _matrix_scan();
-
-    int offset = (isLeftHand) ? 0 : ROWS_PER_HAND;
+static void unselect_col(uint8_t col) { setPinInputHigh(col_pins[col]); }
 
-#if defined(USE_I2C) || defined(EH)
-    for (int i = 0; i < ROWS_PER_HAND; ++i) {
-        i2c_slave_buffer[I2C_KEYMAP_START+i] = matrix[offset+i];
-    }   
-#else // USE_SERIAL
-    // TODO: if MATRIX_COLS > 8 change to pack()
-    for (int i = 0; i < ROWS_PER_HAND; ++i) {
-        serial_s2m_buffer.smatrix[i] = matrix[offset+i];
-    }
-#endif
-    matrix_slave_scan_user();
+static void unselect_cols(void) {
+  for (uint8_t x = 0; x < MATRIX_COLS; x++) {
+    setPinInputHigh(col_pins[x]);
+  }
 }
 
-bool matrix_is_modified(void)
-{
-    if (debouncing) return false;
-    return true;
+static void init_pins(void) {
+  unselect_cols();
+  for (uint8_t x = 0; x < ROWS_PER_HAND; x++) {
+    setPinInputHigh(row_pins[x]);
+  }
 }
 
-inline
-bool matrix_is_on(uint8_t row, uint8_t col)
-{
-    return (matrix[row] & ((matrix_row_t)1<<col));
-}
+static bool read_rows_on_col(matrix_row_t current_matrix[], uint8_t current_col) {
+  bool matrix_changed = false;
 
-inline
-matrix_row_t matrix_get_row(uint8_t row)
-{
-    return matrix[row];
-}
+  // Select col and wait for col selecton to stabilize
+  select_col(current_col);
+  wait_us(30);
+
+  // For each row...
+  for (uint8_t row_index = 0; row_index < ROWS_PER_HAND; row_index++) {
+    // Store last value of row prior to reading
+    matrix_row_t last_row_value = current_matrix[row_index];
 
-void matrix_print(void)
-{
-    print("\nr/c 0123456789ABCDEF\n");
-    for (uint8_t row = 0; row < MATRIX_ROWS; row++) {
-        phex(row); print(": ");
-        pbin_reverse16(matrix_get_row(row));
-        print("\n");
+    // Check row pin state
+    if (readPin(row_pins[row_index])) {
+      // Pin HI, clear col bit
+      current_matrix[row_index] &= ~(ROW_SHIFTER << current_col);
+    } else {
+      // Pin LO, set col bit
+      current_matrix[row_index] |= (ROW_SHIFTER << current_col);
     }
-}
 
-uint8_t matrix_key_count(void)
-{
-    uint8_t count = 0;
-    for (uint8_t i = 0; i < MATRIX_ROWS; i++) {
-        count += bitpop16(matrix[i]);
+    // Determine if the matrix changed state
+    if ((last_row_value != current_matrix[row_index]) && !(matrix_changed)) {
+      matrix_changed = true;
     }
-    return count;
-}
+  }
 
-#if (DIODE_DIRECTION == COL2ROW)
+  // Unselect col
+  unselect_col(current_col);
 
-static void init_cols(void)
-{
-    for(uint8_t x = 0; x < MATRIX_COLS; x++) {
-        setPinInputHigh(col_pins[x]);
-    }
+  return matrix_changed;
 }
 
-static bool read_cols_on_row(matrix_row_t current_matrix[], uint8_t current_row)
-{
-    // Store last value of row prior to reading
-    matrix_row_t last_row_value = current_matrix[current_row];
-
-    // Clear data in matrix row
-    current_matrix[current_row] = 0;
+#endif
 
-    // Select row and wait for row selecton to stabilize
-    select_row(current_row);
-    wait_us(30);
+void matrix_init(void) {
+  debug_enable = true;
+  debug_matrix = true;
+  debug_mouse  = true;
 
-    // For each col...
-    for(uint8_t col_index = 0; col_index < MATRIX_COLS; col_index++) {
-        // Populate the matrix row with the state of the col pin
-        current_matrix[current_row] |=  readPin(col_pins[col_index]) ? 0 : (ROW_SHIFTER << col_index);
+  // Set pinout for right half if pinout for that half is defined
+  if (!isLeftHand) {
+#ifdef MATRIX_ROW_PINS_RIGHT
+    const uint8_t row_pins_right[MATRIX_ROWS] = MATRIX_ROW_PINS_RIGHT;
+    for (uint8_t i = 0; i < MATRIX_ROWS; i++) {
+      row_pins[i] = row_pins_right[i];
     }
+#endif
+#ifdef MATRIX_COL_PINS_RIGHT
+    const uint8_t col_pins_right[MATRIX_COLS] = MATRIX_COL_PINS_RIGHT;
+    for (uint8_t i = 0; i < MATRIX_COLS; i++) {
+      col_pins[i] = col_pins_right[i];
+    }
+#endif
+  }
 
-    // Unselect row
-    unselect_row(current_row);
+  thisHand = isLeftHand ? 0 : (ROWS_PER_HAND);
+  thatHand = ROWS_PER_HAND - thisHand;
 
-    return (last_row_value != current_matrix[current_row]);
-}
+  // initialize key pins
+  init_pins();
 
-static void select_row(uint8_t row)
-{
-    writePinLow(row_pins[row]);
-    setPinOutput(row_pins[row]);
-}
+  // initialize matrix state: all keys off
+  for (uint8_t i = 0; i < MATRIX_ROWS; i++) {
+    matrix[i] = 0;
+  }
 
-static void unselect_row(uint8_t row)
-{
-    setPinInputHigh(row_pins[row]);
-}
+  debounce_init(ROWS_PER_HAND);
 
-static void unselect_rows(void)
-{
-    for(uint8_t x = 0; x < ROWS_PER_HAND; x++) {
-        setPinInputHigh(row_pins[x]);
-    }
+  matrix_init_quantum();
 }
 
+uint8_t _matrix_scan(void) {
+  bool changed = false;
+
+#if defined(DIRECT_PINS) || (DIODE_DIRECTION == COL2ROW)
+  // Set row, read cols
+  for (uint8_t current_row = 0; current_row < ROWS_PER_HAND; current_row++) {
+    changed |= read_cols_on_row(raw_matrix, current_row);
+  }
 #elif (DIODE_DIRECTION == ROW2COL)
+  // Set col, read rows
+  for (uint8_t current_col = 0; current_col < MATRIX_COLS; current_col++) {
+    changed |= read_rows_on_col(raw_matrix, current_col);
+  }
+#endif
 
-static void init_rows(void)
-{
-    for(uint8_t x = 0; x < ROWS_PER_HAND; x++) {
-        setPinInputHigh(row_pins[x]);
-    }
-}
+  debounce(raw_matrix, matrix + thisHand, ROWS_PER_HAND, changed);
 
-static bool read_rows_on_col(matrix_row_t current_matrix[], uint8_t current_col)
-{
-    bool matrix_changed = false;
+  return 1;
+}
 
-    // Select col and wait for col selecton to stabilize
-    select_col(current_col);
-    wait_us(30);
+uint8_t matrix_scan(void) {
+  uint8_t ret = _matrix_scan();
 
-    // For each row...
-    for(uint8_t row_index = 0; row_index < ROWS_PER_HAND; row_index++)
-    {
+  if (is_keyboard_master()) {
+    static uint8_t error_count;
 
-        // Store last value of row prior to reading
-        matrix_row_t last_row_value = current_matrix[row_index];
+    if (!transport_master(matrix + thatHand)) {
+      error_count++;
 
-        // Check row pin state
-        if (readPin(row_pins[row_index]))
-        {
-            // Pin HI, clear col bit
-            current_matrix[row_index] &= ~(ROW_SHIFTER << current_col);
-        }
-        else
-        {
-            // Pin LO, set col bit
-            current_matrix[row_index] |= (ROW_SHIFTER << current_col);
-        }
-
-        // Determine if the matrix changed state
-        if ((last_row_value != current_matrix[row_index]) && !(matrix_changed))
-        {
-            matrix_changed = true;
+      if (error_count > ERROR_DISCONNECT_COUNT) {
+        // reset other half if disconnected
+        for (int i = 0; i < ROWS_PER_HAND; ++i) {
+          matrix[thatHand + i] = 0;
         }
+      }
+    } else {
+      error_count = 0;
     }
 
-    // Unselect col
-    unselect_col(current_col);
-
-    return matrix_changed;
-}
-
-static void select_col(uint8_t col)
-{
-    writePinLow(col_pins[col]);
-    setPinOutput(col_pins[col]);
-}
-
-static void unselect_col(uint8_t col)
-{
-    setPinInputHigh(col_pins[col]);
-}
+    matrix_scan_quantum();
+  } else {
+    transport_slave(matrix + thisHand);
+    matrix_slave_scan_user();
+  }
 
-static void unselect_cols(void)
-{
-    for(uint8_t x = 0; x < MATRIX_COLS; x++) {
-        setPinInputHigh(col_pins[x]);
-    }
+  return ret;
 }
-
-#endif
diff --git a/quantum/split_common/matrix.h b/quantum/split_common/matrix.h
index b5cb45baed..c2bdd3098c 100644
--- a/quantum/split_common/matrix.h
+++ b/quantum/split_common/matrix.h
@@ -1,31 +1,3 @@
-#ifndef SPLIT_COMMON_MATRIX_H
-#define SPLIT_COMMON_MATRIX_H
+#pragma once
 
 #include <common/matrix.h>
-
-#ifdef RGBLIGHT_ENABLE
-#   include "rgblight.h"
-#endif
-
-typedef struct _Serial_m2s_buffer_t {
-#ifdef BACKLIGHT_ENABLE
-    uint8_t backlight_level;
-#endif
-#if defined(RGBLIGHT_ENABLE) && defined(RGBLIGHT_SPLIT)
-    rgblight_config_t rgblight_config; //not yet use
-    //
-    // When MCUs on both sides drive their respective RGB LED chains,
-    // it is necessary to synchronize, so it is necessary to communicate RGB information.
-    // In that case, define the RGBLIGHT_SPLIT macro.
-    //
-    // Otherwise, if the master side MCU drives both sides RGB LED chains,
-    // there is no need to communicate.
-#endif
-} Serial_m2s_buffer_t;
-
-extern volatile Serial_m2s_buffer_t serial_m2s_buffer;
-
-void serial_master_init(void);
-void serial_slave_init(void);
-
-#endif
diff --git a/quantum/split_common/serial.h b/quantum/split_common/serial.h
index b6638b3bde..1c1e640069 100644
--- a/quantum/split_common/serial.h
+++ b/quantum/split_common/serial.h
@@ -1,5 +1,4 @@
-#ifndef SOFT_SERIAL_H
-#define SOFT_SERIAL_H
+#pragma once
 
 #include <stdbool.h>
 
@@ -61,5 +60,3 @@ int  soft_serial_transaction(int sstd_index);
 #ifdef SERIAL_USE_MULTI_TRANSACTION
 int  soft_serial_get_and_clean_status(int sstd_index);
 #endif
-
-#endif /* SOFT_SERIAL_H */
diff --git a/quantum/split_common/split_flags.h b/quantum/split_common/split_flags.h
index f101fff5b5..aaac474a7d 100644
--- a/quantum/split_common/split_flags.h
+++ b/quantum/split_common/split_flags.h
@@ -1,10 +1,9 @@
-#ifndef SPLIT_FLAGS_H
-#define SPLIT_FLAGS_H
+#pragma once
 
 #include <stdbool.h>
 #include <stdint.h>
 
-/** 
+/**
 * Global Flags
 **/
 
@@ -14,7 +13,3 @@ extern volatile bool RGB_DIRTY;
 
 //Backlight Stuff
 extern volatile bool BACKLIT_DIRTY;
-
-
-
-#endif
\ No newline at end of file
diff --git a/quantum/split_common/split_util.c b/quantum/split_common/split_util.c
index e41b6f6386..5095cb8fdc 100644
--- a/quantum/split_common/split_util.c
+++ b/quantum/split_common/split_util.c
@@ -4,142 +4,84 @@
 #include "config.h"
 #include "timer.h"
 #include "split_flags.h"
+#include "transport.h"
 #include "quantum.h"
 
 #ifdef EE_HANDS
 #   include "tmk_core/common/eeprom.h"
-#endif
-
-#ifdef BACKLIGHT_ENABLE
-#   include "backlight.h"
-#endif
-
-#if defined(USE_I2C) || defined(EH)
-#  include "i2c.h"
+#   include "eeconfig.h"
 #endif
 
 volatile bool isLeftHand = true;
 
-volatile uint8_t setTries = 0;
-
-static void setup_handedness(void) {
+__attribute__((weak))
+bool is_keyboard_left(void) {
   #ifdef SPLIT_HAND_PIN
     // Test pin SPLIT_HAND_PIN for High/Low, if low it's right hand
     setPinInput(SPLIT_HAND_PIN);
-    isLeftHand = readPin(SPLIT_HAND_PIN);
+    return readPin(SPLIT_HAND_PIN);
   #else
     #ifdef EE_HANDS
-      isLeftHand = eeprom_read_byte(EECONFIG_HANDEDNESS);
+      return eeprom_read_byte(EECONFIG_HANDEDNESS);
     #else
       #ifdef MASTER_RIGHT
-        isLeftHand = !has_usb();
+        return !is_keyboard_master();
       #else
-        isLeftHand = has_usb();
+        return is_keyboard_master();
       #endif
     #endif
   #endif
 }
 
-static void keyboard_master_setup(void) {
-#if defined(USE_I2C) || defined(EH)
-  i2c_master_init();
-  #ifdef SSD1306OLED
-    matrix_master_OLED_init ();
-  #endif
-#else
-  serial_master_init();
-#endif
+bool is_keyboard_master(void)
+{
+#ifdef __AVR__
+  static enum { UNKNOWN, MASTER, SLAVE } usbstate = UNKNOWN;
 
-    // For master the Backlight info needs to be sent on startup
-    // Otherwise the salve won't start with the proper info until an update
-    BACKLIT_DIRTY = true;
-}
+  // only check once, as this is called often
+  if (usbstate == UNKNOWN)
+  {
+    USBCON |= (1 << OTGPADE);  // enables VBUS pad
+    wait_us(5);
 
-static void keyboard_slave_setup(void) {
-  timer_init();
-#if defined(USE_I2C) || defined(EH)
-    i2c_slave_init(SLAVE_I2C_ADDRESS);
+    usbstate = (USBSTA & (1 << VBUS)) ? MASTER : SLAVE;  // checks state of VBUS
+  }
+
+  return (usbstate == MASTER);
 #else
-    serial_slave_init();
+  return true;
 #endif
 }
 
-bool has_usb(void) {
-   USBCON |= (1 << OTGPADE); //enables VBUS pad
-   _delay_us(5);
-   return (USBSTA & (1<<VBUS));  //checks state of VBUS
-}
-
-void split_keyboard_setup(void) {
-   setup_handedness();
+static void keyboard_master_setup(void) {
+#if defined(USE_I2C) || defined(EH)
+  #ifdef SSD1306OLED
+    matrix_master_OLED_init ();
+  #endif
+#endif
+  transport_master_init();
 
-   if (has_usb()) {
-      keyboard_master_setup();
-   } else {
-      keyboard_slave_setup();
-   }
-   sei();
+  // For master the Backlight info needs to be sent on startup
+  // Otherwise the salve won't start with the proper info until an update
+  BACKLIT_DIRTY = true;
 }
 
-void keyboard_slave_loop(void) {
-   matrix_init();
-
-   //Init RGB
-   #ifdef RGBLIGHT_ENABLE
-      rgblight_init();
-   #endif
-
-   while (1) {
-    // Matrix Slave Scan
-    matrix_slave_scan();
-
-    // Read Backlight Info
-    #ifdef BACKLIGHT_ENABLE
-        #ifdef USE_I2C
-            if (BACKLIT_DIRTY) {
-                backlight_set(i2c_slave_buffer[I2C_BACKLIT_START]);
-                BACKLIT_DIRTY = false;
-            }
-        #else // USE_SERIAL
-            backlight_set(serial_m2s_buffer.backlight_level);
-        #endif
-    #endif
-    // Read RGB Info
-    #ifdef RGBLIGHT_ENABLE
-        #ifdef USE_I2C
-            if (RGB_DIRTY) {
-                // Disable interupts (RGB data is big)
-                cli();
-                // Create new DWORD for RGB data
-                uint32_t dword;
-
-                // Fill the new DWORD with the data that was sent over
-                uint8_t *dword_dat = (uint8_t *)(&dword);
-                for (int i = 0; i < 4; i++) {
-                    dword_dat[i] = i2c_slave_buffer[I2C_RGB_START+i];
-                }
-
-                // Update the RGB now with the new data and set RGB_DIRTY to false
-                rgblight_update_dword(dword);
-                RGB_DIRTY = false;
-                // Re-enable interupts now that RGB is set
-                sei();
-            }
-        #else // USE_SERIAL
-          #ifdef RGBLIGHT_SPLIT
-            // Add serial implementation for RGB here
-          #endif
-        #endif
-    #endif
-   }
+static void keyboard_slave_setup(void)
+{
+  transport_slave_init();
 }
 
 // this code runs before the usb and keyboard is initialized
-void matrix_setup(void) {
-    split_keyboard_setup();
-
-    if (!has_usb()) {
-        //rgblight_init();
-        keyboard_slave_loop();
-    }
+void matrix_setup(void)
+{
+  isLeftHand = is_keyboard_left();
+
+  if (is_keyboard_master())
+  {
+    keyboard_master_setup();
+  }
+  else
+  {
+    keyboard_slave_setup();
+  }
 }
diff --git a/quantum/split_common/split_util.h b/quantum/split_common/split_util.h
index d6cf3e72a9..20f7535bf4 100644
--- a/quantum/split_common/split_util.h
+++ b/quantum/split_common/split_util.h
@@ -1,23 +1,10 @@
-#ifndef SPLIT_KEYBOARD_UTIL_H
-#define SPLIT_KEYBOARD_UTIL_H
+#pragma once
 
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include "eeconfig.h"
-
-#define SLAVE_I2C_ADDRESS           0x32
 
 extern volatile bool isLeftHand;
 
-// slave version of matix scan, defined in matrix.c
-void matrix_slave_scan(void);
-
-void split_keyboard_setup(void);
-bool has_usb(void);
-void keyboard_slave_loop(void);
-
 void matrix_master_OLED_init (void);
-
-#endif
diff --git a/quantum/split_common/transport.c b/quantum/split_common/transport.c
new file mode 100644
index 0000000000..95738530ec
--- /dev/null
+++ b/quantum/split_common/transport.c
@@ -0,0 +1,224 @@
+
+#include "config.h"
+#include "matrix.h"
+#include "quantum.h"
+
+#define ROWS_PER_HAND (MATRIX_ROWS/2)
+
+#ifdef RGBLIGHT_ENABLE
+#   include "rgblight.h"
+#endif
+
+#ifdef BACKLIGHT_ENABLE
+# include "backlight.h"
+  extern backlight_config_t backlight_config;
+#endif
+
+#if defined(USE_I2C) || defined(EH)
+
+#include "i2c.h"
+
+#ifndef SLAVE_I2C_ADDRESS
+#  define SLAVE_I2C_ADDRESS           0x32
+#endif
+
+#if (MATRIX_COLS > 8)
+#  error "Currently only supports 8 COLS"
+#endif
+
+// Get rows from other half over i2c
+bool transport_master(matrix_row_t matrix[]) {
+  int err = 0;
+
+  // write backlight info
+#ifdef BACKLIGHT_ENABLE
+  if (BACKLIT_DIRTY) {
+    err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_WRITE);
+    if (err) { goto i2c_error; }
+
+    // Backlight location
+    err = i2c_master_write(I2C_BACKLIT_START);
+    if (err) { goto i2c_error; }
+
+    // Write backlight
+    i2c_master_write(get_backlight_level());
+
+    BACKLIT_DIRTY = false;
+  }
+#endif
+
+  err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_WRITE);
+  if (err) { goto i2c_error; }
+
+  // start of matrix stored at I2C_KEYMAP_START
+  err = i2c_master_write(I2C_KEYMAP_START);
+  if (err) { goto i2c_error; }
+
+  // Start read
+  err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_READ);
+  if (err) { goto i2c_error; }
+
+  if (!err) {
+    int i;
+    for (i = 0; i < ROWS_PER_HAND-1; ++i) {
+      matrix[i] = i2c_master_read(I2C_ACK);
+    }
+    matrix[i] = i2c_master_read(I2C_NACK);
+    i2c_master_stop();
+  } else {
+i2c_error: // the cable is disconnceted, or something else went wrong
+    i2c_reset_state();
+    return false;
+  }
+
+#ifdef RGBLIGHT_ENABLE
+  if (RGB_DIRTY) {
+    err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_WRITE);
+    if (err) { goto i2c_error; }
+
+    // RGB Location
+    err = i2c_master_write(I2C_RGB_START);
+    if (err) { goto i2c_error; }
+
+    uint32_t dword = eeconfig_read_rgblight();
+
+    // Write RGB
+    err = i2c_master_write_data(&dword, 4);
+    if (err) { goto i2c_error; }
+
+    RGB_DIRTY = false;
+    i2c_master_stop();
+  }
+#endif
+
+  return true;
+}
+
+void transport_slave(matrix_row_t matrix[]) {
+
+  for (int i = 0; i < ROWS_PER_HAND; ++i)
+  {
+    i2c_slave_buffer[I2C_KEYMAP_START + i] = matrix[i];
+  }
+  // Read Backlight Info
+  #ifdef BACKLIGHT_ENABLE
+  if (BACKLIT_DIRTY)
+  {
+    backlight_set(i2c_slave_buffer[I2C_BACKLIT_START]);
+    BACKLIT_DIRTY = false;
+  }
+  #endif
+  #ifdef RGBLIGHT_ENABLE
+  if (RGB_DIRTY)
+  {
+    // Disable interupts (RGB data is big)
+    cli();
+    // Create new DWORD for RGB data
+    uint32_t dword;
+
+    // Fill the new DWORD with the data that was sent over
+    uint8_t * dword_dat = (uint8_t *)(&dword);
+    for (int i = 0; i < 4; i++)
+    {
+      dword_dat[i] = i2c_slave_buffer[I2C_RGB_START + i];
+    }
+
+    // Update the RGB now with the new data and set RGB_DIRTY to false
+    rgblight_update_dword(dword);
+    RGB_DIRTY = false;
+    // Re-enable interupts now that RGB is set
+    sei();
+  }
+  #endif
+}
+
+void transport_master_init(void) {
+  i2c_master_init();
+}
+
+void transport_slave_init(void) {
+  i2c_slave_init(SLAVE_I2C_ADDRESS);
+}
+
+#else // USE_SERIAL
+
+#include "serial.h"
+
+typedef struct _Serial_s2m_buffer_t {
+  // TODO: if MATRIX_COLS > 8 change to uint8_t packed_matrix[] for pack/unpack
+  matrix_row_t smatrix[ROWS_PER_HAND];
+} Serial_s2m_buffer_t;
+
+typedef struct _Serial_m2s_buffer_t {
+#ifdef BACKLIGHT_ENABLE
+    uint8_t backlight_level;
+#endif
+#if defined(RGBLIGHT_ENABLE) && defined(RGBLIGHT_SPLIT)
+    rgblight_config_t rgblight_config; //not yet use
+    //
+    // When MCUs on both sides drive their respective RGB LED chains,
+    // it is necessary to synchronize, so it is necessary to communicate RGB information.
+    // In that case, define the RGBLIGHT_SPLIT macro.
+    //
+    // Otherwise, if the master side MCU drives both sides RGB LED chains,
+    // there is no need to communicate.
+#endif
+} Serial_m2s_buffer_t;
+
+volatile Serial_s2m_buffer_t serial_s2m_buffer = {};
+volatile Serial_m2s_buffer_t serial_m2s_buffer = {};
+uint8_t volatile status0 = 0;
+
+SSTD_t transactions[] = {
+  { (uint8_t *)&status0,
+    sizeof(serial_m2s_buffer), (uint8_t *)&serial_m2s_buffer,
+    sizeof(serial_s2m_buffer), (uint8_t *)&serial_s2m_buffer
+  }
+};
+
+void transport_master_init(void)
+{ soft_serial_initiator_init(transactions, TID_LIMIT(transactions)); }
+
+void transport_slave_init(void)
+{ soft_serial_target_init(transactions, TID_LIMIT(transactions)); }
+
+bool transport_master(matrix_row_t matrix[]) {
+
+  if (soft_serial_transaction()) {
+    return false;
+  }
+
+  // TODO:  if MATRIX_COLS > 8 change to unpack()
+  for (int i = 0; i < ROWS_PER_HAND; ++i) {
+    matrix[i] = serial_s2m_buffer.smatrix[i];
+  }
+
+  #if defined(RGBLIGHT_ENABLE) && defined(RGBLIGHT_SPLIT)
+    // Code to send RGB over serial goes here (not implemented yet)
+  #endif
+
+  #ifdef BACKLIGHT_ENABLE
+    // Write backlight level for slave to read
+    serial_m2s_buffer.backlight_level = backlight_config.enable ? backlight_config.level : 0;
+  #endif
+
+  return true;
+}
+
+void transport_slave(matrix_row_t matrix[]) {
+
+  // TODO: if MATRIX_COLS > 8 change to pack()
+  for (int i = 0; i < ROWS_PER_HAND; ++i)
+  {
+    serial_s2m_buffer.smatrix[i] = matrix[i];
+  }
+  #ifdef BACKLIGHT_ENABLE
+    backlight_set(serial_m2s_buffer.backlight_level);
+  #endif
+  #if defined(RGBLIGHT_ENABLE) && defined(RGBLIGHT_SPLIT)
+  // Add serial implementation for RGB here
+  #endif
+
+}
+
+#endif
diff --git a/quantum/split_common/transport.h b/quantum/split_common/transport.h
new file mode 100644
index 0000000000..ccce57e444
--- /dev/null
+++ b/quantum/split_common/transport.h
@@ -0,0 +1,10 @@
+#pragma once
+
+#include <common/matrix.h>
+
+void transport_master_init(void);
+void transport_slave_init(void);
+
+// returns false if valid data not received from slave
+bool transport_master(matrix_row_t matrix[]);
+void transport_slave(matrix_row_t matrix[]);
diff --git a/tmk_core/common/keyboard.h b/tmk_core/common/keyboard.h
index 71e594a890..ea2f336e9d 100644
--- a/tmk_core/common/keyboard.h
+++ b/tmk_core/common/keyboard.h
@@ -67,6 +67,8 @@ void keyboard_init(void);
 void keyboard_task(void);
 /* it runs when host LED status is updated */
 void keyboard_set_leds(uint8_t leds);
+/* it runs whenever code has to behave differently on a slave */
+bool is_keyboard_master(void);
 
 #ifdef __cplusplus
 }