Add Fourier Keyboard (#2596)

* Initial commit of Fourier keyboard

* Revise keymap, add key to bottom row

* Fix readme

keyboards/fourier/config.h

@@ -0,0 +1,28 @@
+/*
+Copyright 2012 Jun Wako <wakojun@gmail.com>
+Copyright 2015 Jack Humbert
+
+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/>.
+*/
+
+#ifndef CONFIG_H
+#define CONFIG_H
+
+#include "config_common.h"
+
+#ifdef SUBPROJECT_rev1
+    #include "rev1/config.h"
+#endif
+
+#endif

keyboards/fourier/fourier.c

@@ -0,0 +1 @@
+#include "fourier.h"

keyboards/fourier/fourier.h

@@ -0,0 +1,23 @@
+#ifndef FOURIER_H
+#define FOURIER_H
+
+#include "quantum.h"
+
+#ifdef KEYBOARD_fourier_rev1
+    #include "rev1.h"
+#endif
+
+// Used to create a keymap using only KC_ prefixed keys
+#define KC_KEYMAP( \
+    LA1, LA2, LA3, LA4, LA5, LA6, RA1, RA2, RA3, RA4, RA5, RA6, RA7, \
+    LB1, LB2, LB3, LB4, LB5, LB6, RB1, RB2, RB3, RB4, RB5,      RB7, \
+    LC1, LC2, LC3, LC4, LC5, LC6, RC1,      RC3, RC4, RC5, RC6, RC7, \
+    LD1, LD2, LD3, LD4, LD5,      RD1,      RD4, RD5, RD6, RD7 \
+    ) \
+    KEYMAP( \
+        KC_##LA1, KC_##LA2, KC_##LA3, KC_##LA4, KC_##LA5, KC_##LA6, KC_##RA1, KC_##RA2, KC_##RA3, KC_##RA4, KC_##RA5, KC_##RA6, KC_##RA7, \
+        KC_##LB1, KC_##LB2, KC_##LB3, KC_##LB4, KC_##LB5, KC_##LB6, KC_##RB1, KC_##RB2, KC_##RB3, KC_##RB4, KC_##RB5,           KC_##RB7, \
+        KC_##LC1, KC_##LC2, KC_##LC3, KC_##LC4, KC_##LC5, KC_##LC6, KC_##RC1,           KC_##RC3, KC_##RC4, KC_##RC5, KC_##RC6, KC_##RC7, \
+        KC_##LD1, KC_##LD2, KC_##LD3, KC_##LD4, KC_##LD5,           KC_##RD1,                     KC_##RD4, KC_##RD5, KC_##RD6, KC_##RD7 \
+    )
+#endif

keyboards/fourier/i2c.c

@@ -0,0 +1,162 @@
+#include <util/twi.h>
+#include <avr/io.h>
+#include <stdlib.h>
+#include <avr/interrupt.h>
+#include <util/twi.h>
+#include <stdbool.h>
+#include "i2c.h"
+
+#ifdef USE_I2C
+
+// Limits the amount of we wait for any one i2c transaction.
+// Since were running SCL line 100kHz (=> 10μs/bit), and each transactions is
+// 9 bits, a single transaction will take around 90μs to complete.
+//
+// (F_CPU/SCL_CLOCK)  =>  # of μC cycles to transfer a bit
+// poll loop takes at least 8 clock cycles to execute
+#define I2C_LOOP_TIMEOUT (9+1)*(F_CPU/SCL_CLOCK)/8
+
+#define BUFFER_POS_INC() (slave_buffer_pos = (slave_buffer_pos+1)%SLAVE_BUFFER_SIZE)
+
+volatile uint8_t i2c_slave_buffer[SLAVE_BUFFER_SIZE];
+
+static volatile uint8_t slave_buffer_pos;
+static volatile bool slave_has_register_set = false;
+
+// Wait for an i2c operation to finish
+inline static
+void i2c_delay(void) {
+  uint16_t lim = 0;
+  while(!(TWCR & (1<<TWINT)) && lim < I2C_LOOP_TIMEOUT)
+    lim++;
+
+  // easier way, but will wait slightly longer
+  // _delay_us(100);
+}
+
+// Setup twi to run at 100kHz
+void i2c_master_init(void) {
+  // no prescaler
+  TWSR = 0;
+  // Set TWI clock frequency to SCL_CLOCK. Need TWBR>10.
+  // Check datasheets for more info.
+  TWBR = ((F_CPU/SCL_CLOCK)-16)/2;
+}
+
+// Start a transaction with the given i2c slave address. The direction of the
+// transfer is set with I2C_READ and I2C_WRITE.
+// returns: 0 => success
+//          1 => error
+uint8_t i2c_master_start(uint8_t address) {
+  TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTA);
+
+  i2c_delay();
+
+  // check that we started successfully
+  if ( (TW_STATUS != TW_START) && (TW_STATUS != TW_REP_START))
+    return 1;
+
+  TWDR = address;
+  TWCR = (1<<TWINT) | (1<<TWEN);
+
+  i2c_delay();
+
+  if ( (TW_STATUS != TW_MT_SLA_ACK) && (TW_STATUS != TW_MR_SLA_ACK) )
+    return 1; // slave did not acknowledge
+  else
+    return 0; // success
+}
+
+
+// Finish the i2c transaction.
+void i2c_master_stop(void) {
+  TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
+
+  uint16_t lim = 0;
+  while(!(TWCR & (1<<TWSTO)) && lim < I2C_LOOP_TIMEOUT)
+    lim++;
+}
+
+// Write one byte to the i2c slave.
+// returns 0 => slave ACK
+//         1 => slave NACK
+uint8_t i2c_master_write(uint8_t data) {
+  TWDR = data;
+  TWCR = (1<<TWINT) | (1<<TWEN);
+
+  i2c_delay();
+
+  // check if the slave acknowledged us
+  return (TW_STATUS == TW_MT_DATA_ACK) ? 0 : 1;
+}
+
+// Read one byte from the i2c slave. If ack=1 the slave is acknowledged,
+// if ack=0 the acknowledge bit is not set.
+// returns: byte read from i2c device
+uint8_t i2c_master_read(int ack) {
+  TWCR = (1<<TWINT) | (1<<TWEN) | (ack<<TWEA);
+
+  i2c_delay();
+  return TWDR;
+}
+
+void i2c_reset_state(void) {
+  TWCR = 0;
+}
+
+void i2c_slave_init(uint8_t address) {
+  TWAR = address << 0; // slave i2c address
+  // TWEN  - twi enable
+  // TWEA  - enable address acknowledgement
+  // TWINT - twi interrupt flag
+  // TWIE  - enable the twi interrupt
+  TWCR = (1<<TWIE) | (1<<TWEA) | (1<<TWINT) | (1<<TWEN);
+}
+
+ISR(TWI_vect);
+
+ISR(TWI_vect) {
+  uint8_t ack = 1;
+  switch(TW_STATUS) {
+    case TW_SR_SLA_ACK:
+      // this device has been addressed as a slave receiver
+      slave_has_register_set = false;
+      break;
+
+    case TW_SR_DATA_ACK:
+      // this device has received data as a slave receiver
+      // The first byte that we receive in this transaction sets the location
+      // of the read/write location of the slaves memory that it exposes over
+      // i2c.  After that, bytes will be written at slave_buffer_pos, incrementing
+      // slave_buffer_pos after each write.
+      if(!slave_has_register_set) {
+        slave_buffer_pos = TWDR;
+        // don't acknowledge the master if this memory loctaion is out of bounds
+        if ( slave_buffer_pos >= SLAVE_BUFFER_SIZE ) {
+          ack = 0;
+          slave_buffer_pos = 0;
+        }
+        slave_has_register_set = true;
+      } else {
+        i2c_slave_buffer[slave_buffer_pos] = TWDR;
+        BUFFER_POS_INC();
+      }
+      break;
+
+    case TW_ST_SLA_ACK:
+    case TW_ST_DATA_ACK:
+      // master has addressed this device as a slave transmitter and is
+      // requesting data.
+      TWDR = i2c_slave_buffer[slave_buffer_pos];
+      BUFFER_POS_INC();
+      break;
+
+    case TW_BUS_ERROR: // something went wrong, reset twi state
+      TWCR = 0;
+    default:
+      break;
+  }
+  // Reset everything, so we are ready for the next TWI interrupt
+  TWCR |= (1<<TWIE) | (1<<TWINT) | (ack<<TWEA) | (1<<TWEN);
+}
+#endif

keyboards/fourier/i2c.h

@@ -0,0 +1,49 @@
+#ifndef I2C_H
+#define I2C_H
+
+#include <stdint.h>
+
+#ifndef F_CPU
+#define F_CPU 16000000UL
+#endif
+
+#define I2C_READ 1
+#define I2C_WRITE 0
+
+#define I2C_ACK 1
+#define I2C_NACK 0
+
+#define SLAVE_BUFFER_SIZE 0x10
+
+// i2c SCL clock frequency
+#define SCL_CLOCK  400000L
+
+extern volatile uint8_t i2c_slave_buffer[SLAVE_BUFFER_SIZE];
+
+void i2c_master_init(void);
+uint8_t i2c_master_start(uint8_t address);
+void i2c_master_stop(void);
+uint8_t i2c_master_write(uint8_t data);
+uint8_t i2c_master_read(int);
+void i2c_reset_state(void);
+void i2c_slave_init(uint8_t address);
+
+
+static inline unsigned char i2c_start_read(unsigned char addr) {
+  return i2c_master_start((addr << 1) | I2C_READ);
+}
+
+static inline unsigned char i2c_start_write(unsigned char addr) {
+  return i2c_master_start((addr << 1) | I2C_WRITE);
+}
+
+// from SSD1306 scrips
+extern unsigned char i2c_rep_start(unsigned char addr);
+extern void i2c_start_wait(unsigned char addr);
+extern unsigned char i2c_readAck(void);
+extern unsigned char i2c_readNak(void);
+extern unsigned char i2c_read(unsigned char ack);
+
+#define i2c_read(ack)  (ack) ? i2c_readAck() : i2c_readNak();
+
+#endif

keyboards/fourier/keymaps/default/config.h

@@ -0,0 +1,31 @@
+/*
+This is the c configuration file for the keymap
+
+Copyright 2012 Jun Wako <wakojun@gmail.com>
+Copyright 2015 Jack Humbert
+
+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/>.
+*/
+
+#ifndef CONFIG_USER_H
+#define CONFIG_USER_H
+
+#include "config_common.h"
+
+/* Use I2C or Serial, not both */
+
+#define USE_SERIAL
+// #define USE_I2C
+
+#endif

keyboards/fourier/keymaps/default/keymap.c

@@ -0,0 +1,76 @@
+#include "fourier.h"
+#include "action_layer.h"
+#include "eeconfig.h"
+
+extern keymap_config_t keymap_config;
+
+// Each layer gets a name for readability, which is then used in the keymap matrix below.
+// The underscores don't mean anything - you can have a layer called STUFF or any other name.
+// Layer names don't all need to be of the same length, obviously, and you can also skip them
+// entirely and just use numbers.
+#define _BASE 0
+#define _FN1 1
+#define _FN2 2
+
+enum custom_keycodes {
+  QWERTY = SAFE_RANGE,
+};
+
+#define KC_ KC_TRNS
+#define _______ KC_TRNS
+#define XXXXXXX KC_NO
+#define KC_FN1 MO(_FN1)
+#define KC_FN2 MO(_FN2)
+#define KC_SPFN1 LT(_FN1, KC_SPACE)
+#define KC_SPFN2 LT(_FN2, KC_SPACE)
+#define KC_BSFN1 LT(_FN1, KC_BSPC)
+#define KC_BSFN2 LT(_FN2, KC_BSPC)
+#define KC_RST RESET
+#define KC_DBUG DEBUG
+#define KC_RTOG RGB_TOG
+#define KC_RMOD RGB_MOD
+#define KC_RHUI RGB_HUI
+#define KC_RHUD RGB_HUD
+#define KC_RSAI RGB_SAI
+#define KC_RSAD RGB_SAD
+#define KC_RVAI RGB_VAI
+#define KC_RVAD RGB_VAD
+
+const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
+  [_BASE] = KC_KEYMAP(
+ //,----+----+----+----+----+----|----+----+----+----+----+----+----.
+    ESC , Q  , W  , E  , R  , T  , Y  , U  , I  , O  , P  ,DEL ,BSPC,
+ //|----`----`----`----`----`----|----`----`----`----`----`----`----|
+    TAB  , A  , S  , D  , F  , G  , H  , J  , K  , L  ,QUOT, ENTER  ,
+ //|-----`----`----`----`----`----|----`----`----`----`----`--------|
+    LSFT   , Z  , X  , C  , V  , B  , N  , M  ,COMM,DOT ,SLSH, RSFT ,
+ //|-------`----`----`----`----`----|----`----`----`----`----`------|
+    LCTL ,LALT,LGUI ,FN1 , SPFN1  ,  BSFN2 ,RGUI ,RALT , FN2 , RCTL 
+ //`-----+----+-----+----+--------|--------+-----+-----+-----+------'
+  ),
+
+  [_FN1] = KC_KEYMAP(
+ //,----+----+----+----+----+----|----+----+----+----+----+----+----.
+    GRV , 1  , 2  , 3  , 4  , 5  , 6  , 7  , 8  , 9  , 0  ,MINS,EQL ,
+ //|----`----`----`----`----`----|----`----`----`----`----`----`----|
+    RST  ,RHUI,RSAI,RVAI,VOLU,LBRC,RBRC, 4  , 5  , 6  ,SCLN,        ,
+ //|-----`----`----`----`----`----|----`----`----`----`----`--------|
+    RMOD   ,RHUD,RSAD,RVAD,VOLD,LCBR,RCBR, 1  , 2  , 3  , UP ,      ,
+ //|-------`----`----`----`----`----|----`----`----`----`----`------|
+    RTOG ,    ,     ,    ,        ,  DEL   ,  0  ,LEFT ,DOWN , RGHT 
+ //`-----+----+-----+----+--------|--------+-----+-----+-----+------'
+  ),
+
+  [_FN2] = KC_KEYMAP(
+ //,----+----+----+----+----+----|----+----+----+----+----+----+----.
+    TILD,EXLM, AT ,HASH,DLR ,PERC,CIRC,AMPR,ASTR,LPRN,RPRN,UNDS,PLUS,
+ //|----`----`----`----`----`----|----`----`----`----`----`----`----|
+         ,    ,    ,INS ,PGUP,HOME,    ,    ,    ,    ,COLN,        ,
+ //|-----`----`----`----`----`----|----`----`----`----`----`--------|
+           ,    ,    ,DEL ,PGDN,END ,    ,    ,    ,    ,    ,      ,
+ //|-------`----`----`----`----`----|----`----`----`----`----`------|
+         ,    ,     ,    ,  DEL   ,        ,     ,     ,     ,      
+ //`-----+----+-----+----+--------|--------+-----+-----+-----+------'
+  )
+
+};

keyboards/fourier/keymaps/default/rules.mk

@@ -0,0 +1,3 @@
+ifndef QUANTUM_DIR
+	include ../../../../Makefile
+endif

keyboards/fourier/matrix.c

@@ -0,0 +1,468 @@
+/*
+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 "backlight.h"
+
+#ifdef USE_I2C
+#  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 (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
+static matrix_row_t matrix_debouncing[MATRIX_ROWS];
+
+#define ERROR_DISCONNECT_COUNT 5
+
+#define SERIAL_LED_ADDR 0x00
+
+#define ROWS_PER_HAND (MATRIX_ROWS/2)
+
+static uint8_t error_count = 0;
+
+static const uint8_t row_pins[MATRIX_ROWS] = MATRIX_ROW_PINS;
+static const uint8_t col_pins[MATRIX_COLS] = MATRIX_COL_PINS;
+
+/* 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
+
+__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) {
+}
+
+inline
+uint8_t matrix_rows(void)
+{
+    return MATRIX_ROWS;
+}
+
+inline
+uint8_t matrix_cols(void)
+{
+    return MATRIX_COLS;
+}
+
+void matrix_init(void)
+{
+    debug_enable = true;
+    debug_matrix = true;
+    debug_mouse = true;
+    // initialize row and col
+    unselect_rows();
+    init_cols();
+
+    TX_RX_LED_INIT;
+
+    // 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();
+                PORTD ^= (1 << 2);
+            }
+
+#       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
+
+    }
+#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;
+}
+
+#ifdef USE_I2C
+
+// Get rows from other half over i2c
+int i2c_transaction(void) {
+    int slaveOffset = (isLeftHand) ? (ROWS_PER_HAND) : 0;
+
+    int err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_WRITE);
+    if (err) goto i2c_error;
+
+    // start of matrix stored at 0x00
+    err = i2c_master_write(0x00);
+    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;
+    }
+
+    return 0;
+}
+
+#else // USE_SERIAL
+
+int serial_transaction(void) {
+    int slaveOffset = (isLeftHand) ? (ROWS_PER_HAND) : 0;
+
+    if (serial_update_buffers()) {
+        return 1;
+    }
+
+    for (int i = 0; i < ROWS_PER_HAND; ++i) {
+        matrix[slaveOffset+i] = serial_slave_buffer[i];
+    }
+
+#ifdef BACKLIGHT_ENABLE
+    // Write backlight level for slave to read
+    serial_master_buffer[SERIAL_LED_ADDR] = get_backlight_level();
+#endif
+    return 0;
+}
+#endif
+
+uint8_t matrix_scan(void)
+{
+    uint8_t ret = _matrix_scan();
+
+#ifdef USE_I2C
+    if( i2c_transaction() ) {
+#else // USE_SERIAL
+    if( serial_transaction() ) {
+#endif
+        // turn on the indicator led when halves are disconnected
+        TXLED1;
+
+        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 {
+        // turn off the indicator led on no error
+        TXLED0;
+        error_count = 0;
+    }
+    matrix_scan_quantum();
+    return ret;
+}
+
+void matrix_slave_scan(void) {
+    _matrix_scan();
+
+    int offset = (isLeftHand) ? 0 : ROWS_PER_HAND;
+
+#ifdef USE_I2C
+    for (int i = 0; i < ROWS_PER_HAND; ++i) {
+        i2c_slave_buffer[i] = matrix[offset+i];
+    }
+#else // USE_SERIAL
+    for (int i = 0; i < ROWS_PER_HAND; ++i) {
+        serial_slave_buffer[i] = matrix[offset+i];
+    }
+
+#ifdef BACKLIGHT_ENABLE
+    // Read backlight level sent from master and update level on slave
+    backlight_set(serial_master_buffer[SERIAL_LED_ADDR]);
+#endif
+#endif
+}
+
+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
+    }
+}
+
+#endif

keyboards/fourier/readme.md

@@ -0,0 +1,20 @@
+Fourier
+========
+
+A split 40% staggered keyboard made and sold by Keebio. [More info at Keebio](https://keeb.io).
+
+Keyboard Maintainer: [Bakingpy/nooges](https://github.com/nooges)  
+Hardware Supported: Pro Micro  
+Hardware Availability: [Keebio](https://keeb.io)  
+
+Make example for this keyboard (after setting up your build environment):
+
+    make fourier/rev1:default
+
+Example of flashing this keyboard:
+
+    make fourier/rev1:default:avrdude
+
+See [build environment setup](https://docs.qmk.fm/build_environment_setup.html) then the [make instructions](https://docs.qmk.fm/make_instructions.html) for more information.
+
+A build guide for this keyboard can be found here: [Keebio Build Guides](https://docs.keeb.io)

keyboards/fourier/rev1/config.h

@@ -0,0 +1,84 @@
+/*
+Copyright 2012 Jun Wako <wakojun@gmail.com>
+Copyright 2015 Jack Humbert
+
+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/>.
+*/
+
+#ifndef REV1_CONFIG_H
+#define REV1_CONFIG_H
+
+#include "../config.h"
+
+/* USB Device descriptor parameter */
+#define VENDOR_ID       0xCB10
+#define PRODUCT_ID      0x1247
+#define DEVICE_VER      0x0100
+#define MANUFACTURER    Keebio
+#define PRODUCT         Fourier
+#define DESCRIPTION     Split 40 percent staggered keyboard
+
+/* key matrix size */
+// Rows are doubled-up
+#define MATRIX_ROWS 8
+#define MATRIX_COLS 7
+
+// wiring of each half
+#define MATRIX_ROW_PINS { F4, D7, E6, B4 }
+#define MATRIX_COL_PINS { F5, F6, F7, B1, B3, B2, B6 }
+
+/* define if matrix has ghost */
+//#define MATRIX_HAS_GHOST
+
+/* Set 0 if debouncing isn't needed */
+#define DEBOUNCING_DELAY 5
+
+/* Mechanical locking support. Use KC_LCAP, KC_LNUM or KC_LSCR instead in keymap */
+#define LOCKING_SUPPORT_ENABLE
+/* Locking resynchronize hack */
+#define LOCKING_RESYNC_ENABLE
+
+/* key combination for command */
+#define IS_COMMAND() ( \
+    keyboard_report->mods == (MOD_BIT(KC_LSHIFT) | MOD_BIT(KC_RSHIFT)) \
+)
+
+/* ws2812 RGB LED */
+#define RGB_DI_PIN D3
+#define RGBLIGHT_TIMER
+#define RGBLIGHT_ANIMATIONS
+#define RGBLED_NUM 14    // Number of LEDs
+#define ws2812_PORTREG  PORTD
+#define ws2812_DDRREG   DDRD
+
+/*
+ * Feature disable options
+ *  These options are also useful to firmware size reduction.
+ */
+
+/* disable debug print */
+// #define NO_DEBUG
+
+/* disable print */
+// #define NO_PRINT
+
+/* disable action features */
+//#define NO_ACTION_LAYER
+//#define NO_ACTION_TAPPING
+//#define NO_ACTION_ONESHOT
+//#define NO_ACTION_MACRO
+//#define NO_ACTION_FUNCTION
+
+
+#endif

keyboards/fourier/rev1/rev1.c

@@ -0,0 +1,7 @@
+#include "fourier.h"
+
+
+void matrix_init_kb(void) {
+	matrix_init_user();
+};
+

keyboards/fourier/rev1/rev1.h

@@ -0,0 +1,34 @@
+#ifndef REV1_H
+#define REV1_H
+
+#include "../fourier.h"
+
+#include "quantum.h"
+
+
+#ifdef USE_I2C
+#include <stddef.h>
+#ifdef __AVR__
+	#include <avr/io.h>
+	#include <avr/interrupt.h>
+#endif
+#endif
+
+#define KEYMAP( \
+	LA1, LA2, LA3, LA4, LA5, LA6, RA1, RA2, RA3, RA4, RA5, RA6, RA7, \
+	LB1, LB2, LB3, LB4, LB5, LB6, RB1, RB2, RB3, RB4, RB5,      RB7, \
+	LC1, LC2, LC3, LC4, LC5, LC6, RC1,      RC3, RC4, RC5, RC6, RC7, \
+	LD1, LD2, LD3, LD4, LD5,      RD1,           RD4, RD5, RD6, RD7 \
+	) \
+	{ \
+		{ LA1, LA2, LA3, LA4, LA5, LA6, KC_NO}, \
+		{ LB1, LB2, LB3, LB4, LB5, LB6, KC_NO}, \
+		{ LC1, LC2, LC3, LC4, LC5, LC6, KC_NO}, \
+		{ LD1, LD2, LD3, LD4, LD5, KC_NO, KC_NO}, \
+		{ RA1, RA2, RA3, RA4, RA5, RA6, RA7}, \
+		{ RB1, RB2, RB3, RB4, RB5, KC_NO, RB7}, \
+		{ RC1, KC_NO, RC3, RC4, RC5, RC6, RC7}, \
+		{ RD1, KC_NO, KC_NO, RD4, RD5, RD6, RD7} \
+	}
+
+#endif

keyboards/fourier/rules.mk

@@ -0,0 +1,74 @@
+SRC += matrix.c \
+	   i2c.c \
+	   split_util.c \
+	   serial.c
+
+# MCU name
+#MCU = at90usb1287
+MCU = atmega32u4
+
+# Processor frequency.
+#     This will define a symbol, F_CPU, in all source code files equal to the
+#     processor frequency in Hz. You can then use this symbol in your source code to
+#     calculate timings. Do NOT tack on a 'UL' at the end, this will be done
+#     automatically to create a 32-bit value in your source code.
+#
+#     This will be an integer division of F_USB below, as it is sourced by
+#     F_USB after it has run through any CPU prescalers. Note that this value
+#     does not *change* the processor frequency - it should merely be updated to
+#     reflect the processor speed set externally so that the code can use accurate
+#     software delays.
+F_CPU = 16000000
+
+#
+# LUFA specific
+#
+# Target architecture (see library "Board Types" documentation).
+ARCH = AVR8
+
+# Input clock frequency.
+#     This will define a symbol, F_USB, in all source code files equal to the
+#     input clock frequency (before any prescaling is performed) in Hz. This value may
+#     differ from F_CPU if prescaling is used on the latter, and is required as the
+#     raw input clock is fed directly to the PLL sections of the AVR for high speed
+#     clock generation for the USB and other AVR subsections. Do NOT tack on a 'UL'
+#     at the end, this will be done automatically to create a 32-bit value in your
+#     source code.
+#
+#     If no clock division is performed on the input clock inside the AVR (via the
+#     CPU clock adjust registers or the clock division fuses), this will be equal to F_CPU.
+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 
+#     automatically (+60). See bootloader.mk for all options.
+BOOTLOADER = caterina
+
+# Interrupt driven control endpoint task(+60)
+OPT_DEFS += -DINTERRUPT_CONTROL_ENDPOINT
+
+# Build Options
+#   change to "no" to disable the options, or define them in the Makefile in
+#   the appropriate keymap folder that will get included automatically
+#
+BOOTMAGIC_ENABLE = no       # Virtual DIP switch configuration(+1000)
+MOUSEKEY_ENABLE = no        # Mouse keys(+4700)
+EXTRAKEY_ENABLE = yes       # Audio control and System control(+450)
+CONSOLE_ENABLE = no         # Console for debug(+400)
+COMMAND_ENABLE = yes        # Commands for debug and configuration
+NKRO_ENABLE = no            # Nkey Rollover - if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
+BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
+MIDI_ENABLE = no            # MIDI controls
+AUDIO_ENABLE = no           # Audio output on port C6
+UNICODE_ENABLE = no         # Unicode
+BLUETOOTH_ENABLE = no       # Enable Bluetooth with the Adafruit EZ-Key HID
+RGBLIGHT_ENABLE = yes        # Enable WS2812 RGB underlight.  Do not enable this with audio at the same time.
+SUBPROJECT_rev1 = yes
+USE_I2C = 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
+
+DEFAULT_FOLDER = fourier/rev1

keyboards/fourier/serial.c

@@ -0,0 +1,228 @@
+/*
+ * WARNING: be careful changing this code, it is very timing dependent
+ */
+
+#ifndef F_CPU
+#define F_CPU 16000000
+#endif
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <util/delay.h>
+#include <stdbool.h>
+#include "serial.h"
+
+#ifndef USE_I2C
+
+// Serial pulse period in microseconds. Its probably a bad idea to lower this
+// value.
+#define SERIAL_DELAY 24
+
+uint8_t volatile serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH] = {0};
+uint8_t volatile serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH] = {0};
+
+#define SLAVE_DATA_CORRUPT (1<<0)
+volatile uint8_t status = 0;
+
+inline static
+void serial_delay(void) {
+  _delay_us(SERIAL_DELAY);
+}
+
+inline static
+void serial_output(void) {
+  SERIAL_PIN_DDR |= SERIAL_PIN_MASK;
+}
+
+// make the serial pin an input with pull-up resistor
+inline static
+void serial_input(void) {
+  SERIAL_PIN_DDR  &= ~SERIAL_PIN_MASK;
+  SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
+}
+
+inline static
+uint8_t serial_read_pin(void) {
+  return !!(SERIAL_PIN_INPUT & SERIAL_PIN_MASK);
+}
+
+inline static
+void serial_low(void) {
+  SERIAL_PIN_PORT &= ~SERIAL_PIN_MASK;
+}
+
+inline static
+void serial_high(void) {
+  SERIAL_PIN_PORT |= SERIAL_PIN_MASK;
+}
+
+void serial_master_init(void) {
+  serial_output();
+  serial_high();
+}
+
+void serial_slave_init(void) {
+  serial_input();
+
+  // Enable INT0
+  EIMSK |= _BV(INT0);
+  // Trigger on falling edge of INT0
+  EICRA &= ~(_BV(ISC00) | _BV(ISC01));
+}
+
+// Used by the master to synchronize timing with the slave.
+static
+void sync_recv(void) {
+  serial_input();
+  // This shouldn't hang if the slave disconnects because the
+  // serial line will float to high if the slave does disconnect.
+  while (!serial_read_pin());
+  serial_delay();
+}
+
+// Used by the slave to send a synchronization signal to the master.
+static
+void sync_send(void) {
+  serial_output();
+
+  serial_low();
+  serial_delay();
+
+  serial_high();
+}
+
+// Reads a byte from the serial line
+static
+uint8_t serial_read_byte(void) {
+  uint8_t byte = 0;
+  serial_input();
+  for ( uint8_t i = 0; i < 8; ++i) {
+    byte = (byte << 1) | serial_read_pin();
+    serial_delay();
+    _delay_us(1);
+  }
+
+  return byte;
+}
+
+// Sends a byte with MSB ordering
+static
+void serial_write_byte(uint8_t data) {
+  uint8_t b = 8;
+  serial_output();
+  while( b-- ) {
+    if(data & (1 << b)) {
+      serial_high();
+    } else {
+      serial_low();
+    }
+    serial_delay();
+  }
+}
+
+// interrupt handle to be used by the slave device
+ISR(SERIAL_PIN_INTERRUPT) {
+  sync_send();
+
+  uint8_t checksum = 0;
+  for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
+    serial_write_byte(serial_slave_buffer[i]);
+    sync_send();
+    checksum += serial_slave_buffer[i];
+  }
+  serial_write_byte(checksum);
+  sync_send();
+
+  // wait for the sync to finish sending
+  serial_delay();
+
+  // read the middle of pulses
+  _delay_us(SERIAL_DELAY/2);
+
+  uint8_t checksum_computed = 0;
+  for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
+    serial_master_buffer[i] = serial_read_byte();
+    sync_send();
+    checksum_computed += serial_master_buffer[i];
+  }
+  uint8_t checksum_received = serial_read_byte();
+  sync_send();
+
+  serial_input(); // end transaction
+
+  if ( checksum_computed != checksum_received ) {
+    status |= SLAVE_DATA_CORRUPT;
+  } else {
+    status &= ~SLAVE_DATA_CORRUPT;
+  }
+}
+
+inline
+bool serial_slave_DATA_CORRUPT(void) {
+  return status & SLAVE_DATA_CORRUPT;
+}
+
+// Copies the serial_slave_buffer to the master and sends the
+// serial_master_buffer to the slave.
+//
+// Returns:
+// 0 => no error
+// 1 => slave did not respond
+int serial_update_buffers(void) {
+  // this code is very time dependent, so we need to disable interrupts
+  cli();
+
+  // signal to the slave that we want to start a transaction
+  serial_output();
+  serial_low();
+  _delay_us(1);
+
+  // wait for the slaves response
+  serial_input();
+  serial_high();
+  _delay_us(SERIAL_DELAY);
+
+  // check if the slave is present
+  if (serial_read_pin()) {
+    // slave failed to pull the line low, assume not present
+    sei();
+    return 1;
+  }
+
+  // if the slave is present syncronize with it
+  sync_recv();
+
+  uint8_t checksum_computed = 0;
+  // receive data from the slave
+  for (int i = 0; i < SERIAL_SLAVE_BUFFER_LENGTH; ++i) {
+    serial_slave_buffer[i] = serial_read_byte();
+    sync_recv();
+    checksum_computed += serial_slave_buffer[i];
+  }
+  uint8_t checksum_received = serial_read_byte();
+  sync_recv();
+
+  if (checksum_computed != checksum_received) {
+    sei();
+    return 1;
+  }
+
+  uint8_t checksum = 0;
+  // send data to the slave
+  for (int i = 0; i < SERIAL_MASTER_BUFFER_LENGTH; ++i) {
+    serial_write_byte(serial_master_buffer[i]);
+    sync_recv();
+    checksum += serial_master_buffer[i];
+  }
+  serial_write_byte(checksum);
+  sync_recv();
+
+  // always, release the line when not in use
+  serial_output();
+  serial_high();
+
+  sei();
+  return 0;
+}
+
+#endif

keyboards/fourier/serial.h

@@ -0,0 +1,26 @@
+#ifndef MY_SERIAL_H
+#define MY_SERIAL_H
+
+#include "config.h"
+#include <stdbool.h>
+
+/* TODO:  some defines for interrupt setup */
+#define SERIAL_PIN_DDR DDRD
+#define SERIAL_PIN_PORT PORTD
+#define SERIAL_PIN_INPUT PIND
+#define SERIAL_PIN_MASK _BV(PD0)
+#define SERIAL_PIN_INTERRUPT INT0_vect
+
+#define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
+#define SERIAL_MASTER_BUFFER_LENGTH 1
+
+// Buffers for master - slave communication
+extern volatile uint8_t serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH];
+extern volatile uint8_t serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH];
+
+void serial_master_init(void);
+void serial_slave_init(void);
+int serial_update_buffers(void);
+bool serial_slave_data_corrupt(void);
+
+#endif

keyboards/fourier/split_util.c

@@ -0,0 +1,80 @@
+#include <avr/io.h>
+#include <avr/wdt.h>
+#include <avr/power.h>
+#include <avr/interrupt.h>
+#include <util/delay.h>
+#include <avr/eeprom.h>
+#include "split_util.h"
+#include "matrix.h"
+#include "keyboard.h"
+#include "config.h"
+#include "timer.h"
+#include "pincontrol.h"
+
+#ifdef USE_I2C
+#  include "i2c.h"
+#else
+#  include "serial.h"
+#endif
+
+volatile bool isLeftHand = true;
+
+static void setup_handedness(void) {
+  // Test D2 pin for handedness, if D2 is grounded, it's the right hand
+  pinMode(D2, PinDirectionInput);
+  isLeftHand = digitalRead(D2);
+}
+
+static void keyboard_master_setup(void) {
+#ifdef USE_I2C
+    i2c_master_init();
+#ifdef SSD1306OLED
+    matrix_master_OLED_init();
+#endif
+#else
+    serial_master_init();
+#endif
+}
+
+static void keyboard_slave_setup(void) {
+  timer_init();
+#ifdef USE_I2C
+    i2c_slave_init(SLAVE_I2C_ADDRESS);
+#else
+    serial_slave_init();
+#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();
+
+   if (has_usb()) {
+      keyboard_master_setup();
+   } else {
+      keyboard_slave_setup();
+   }
+   sei();
+}
+
+void keyboard_slave_loop(void) {
+   matrix_init();
+
+   while (1) {
+      matrix_slave_scan();
+   }
+}
+
+// this code runs before the usb and keyboard is initialized
+void matrix_setup(void) {
+    split_keyboard_setup();
+
+    if (!has_usb()) {
+        keyboard_slave_loop();
+    }
+}

keyboards/fourier/split_util.h

@@ -0,0 +1,20 @@
+#ifndef SPLIT_KEYBOARD_UTIL_H
+#define SPLIT_KEYBOARD_UTIL_H
+
+#include <stdbool.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