6 files changed, 494 insertions, 107 deletions

diff --git a/quantum/keymap_extras/keymap_br_abnt2.h b/quantum/keymap_extras/keymap_br_abnt2.h
new file mode 100644
index 000000000..0df177721
--- /dev/null
+++ b/quantum/keymap_extras/keymap_br_abnt2.h
@@ -0,0 +1,58 @@
+#ifndef KEYMAP_BR_ABNT2_H
+#define KEYMAP_BR_ABNT2_H
+
+#include "keymap_common.h"
+
+/* Scan codes for the Brazilian ABNT2 keyboard layout */
+
+#define BR_CCDL KC_SCLN      //  Ç   same scancode as ;: on US layout
+#define BR_SCLN KC_SLSH      //  ;:  same scancode as /? on US layout
+#define BR_QUOT KC_GRV       //  '"  same scancode as `~ on US layout
+#define BR_TILD KC_QUOT      //  ~^  dead keys, same scancode as '" on US layout
+#define BR_ACUT KC_LBRC      //  ´`  dead keys, same scancode as [{ on US layout
+#define BR_LBRC KC_RBRC      //  [{  same scancode as ]} on US layout
+#define BR_RBRC KC_BSLS      //  ]}  same scancode as \| on US layout
+#define BR_BSLS KC_NUBS      //  \|  uses the non-US hash scancode (#~, sometimes §±)
+#define BR_SLSH KC_INT1      //  /?  uses the INTL1 scancode
+
+#define BR_COLN LSFT(BR_SCLN)   // shifted :
+#define BR_DQT  LSFT(BR_QUOT)   // shifted "
+#define BR_CIRC LSFT(BR_TILD)   // shifted ^ (dead key)
+#define BR_GRAV LSFT(BR_ACUT)   // shifted ` (dead key)
+#define BR_LCBR LSFT(BR_LBRC)   // shifted {
+#define BR_RCBR LSFT(BR_RBRC)   // shifted }
+#define BR_PIPE LSFT(BR_BSLS)   // shifted |
+#define BR_QUES LSFT(BR_SLSH)   // shifted ?
+#define BR_TRMA LSFT(KC_6)      // shifted ¨ (dead key - trema accent)
+
+// On the ABNT2 the keypad comma and the keypad dot scancodes are switched
+// (presumably because in Brazil comma is used as the decimal separator)
+#define BR_KPDT KC_KP_COMMA  //  keypad .
+#define BR_KPCM KC_KP_DOT    //  keypad ,
+
+#define BR_1UP    LALT(KC_1)      // 1 superscript                    ¹   alt+1
+#define BR_2UP    LALT(KC_2)      // 2 superscript                    ²   alt+2
+#define BR_3UP    LALT(KC_3)      // 3 superscript                    ³   alt+3
+#define BR_PND    LALT(KC_4)      // Pound sign                       £   alt+4
+#define BR_CENT   LALT(KC_5)      // Cent sign                        ¢   alt+5
+#define BR_NOT    LALT(KC_6)      // Not sign                         ¬   alt+6
+#define BR_SECT   LALT(KC_EQL)    // Section sign                     §   alt+=
+#define BR_FORD   LALT(BR_LBRC)   // Feminine Ordinal Sign            ª   alt+[
+#define BR_MORD   LALT(BR_RBRC)   // Masculine Ordinal Sign           º   alt+]
+#define BR_DGRE   LALT(BR_SLSH)   // Degree sign                      °   alt+/
+
+#define BR_EURO   LALT(KC_E)      // Euro sign                        €   alt+e
+#define BR_NDTD   LALT(BR_TILD)   // Non-dead key tilde               ~   alt+~
+#define BR_NDAC   LALT(BR_ACUT)   // Non-dead key acute accent        ´   alt+´
+#define BR_NDGV   LALT(BR_QUOT)   // Non-dead key grave accent        `   alt+'
+#define BR_NDCR   LALT(BR_CIRC)   // Non-dead key circumflex accent   ^   alt+^ (alt+shift+~)
+#define BR_NDTR   LALT(BR_TRMA)   // Non-dead key trema accent        ¨   alt+¨ (alt+shift+6)
+
+// For 101-key keyboard layouts, the ABNT2 layout allows
+// the slash and question mark to be typed using alt+q and alt+w.
+// The shortcuts are provided here for completeness' sake,
+// but it's recommended to use BR_SLSH and BR_QUES instead
+#define BR_ASLS   LALT(KC_Q)
+#define BR_AQST   LALT(KC_W)
+
+#endif
diff --git a/quantum/keymap_extras/keymap_jp.h b/quantum/keymap_extras/keymap_jp.h
new file mode 100644
index 000000000..e81b5952e
--- /dev/null
+++ b/quantum/keymap_extras/keymap_jp.h
@@ -0,0 +1,62 @@
+/* JP106-layout (Japanese Standard)
+ *
+ * For more information, see
+ * http://www2d.biglobe.ne.jp/~msyk/keyboard/layout/usbkeycode.html
+ * note: This website is written in Japanese.
+ */
+
+
+#ifndef KEYMAP_JP_H
+#define KEYMAP_JP_H
+
+
+#include "keymap.h"
+
+
+#define JP_ZHTG KC_GRV  // hankaku/zenkaku|kanzi
+#define JP_YEN  KC_INT3 // yen, |
+#define JP_CIRC KC_EQL  // ^, ~
+#define JP_AT   KC_LBRC // @, `
+#define JP_LBRC KC_RBRC // [, {
+#define JP_COLN KC_QUOT // :, *
+#define JP_RBRC KC_NUHS // ], }
+#define JP_BSLS KC_INT1 // \, _
+#define JP_MHEN KC_INT5 // muhenkan
+#define JP_HENK KC_INT4 // henkan
+#define JP_KANA KC_INT2 // katakana/hiragana|ro-mazi
+
+
+//Aliases for shifted symbols
+#define JP_DQT  LSFT(KC_2)    // "
+#define JP_AMPR LSFT(KC_6)    // &
+#define JP_QUOT LSFT(KC_7)    // '
+#define JP_LPRN LSFT(KC_8)    // (
+#define JP_RPRN LSFT(KC_9)    // )
+#define JP_EQL  LSFT(KC_MINS) // =
+#define JP_TILD LSFT(JP_CIRC) // ~
+#define JP_PIPE LSFT(JP_YEN)  // |
+#define JP_GRV  LSFT(JP_AT)   // `
+#define JP_LCBR LSFT(JP_LBRC) // {
+#define JP_PLUS LSFT(KC_SCLN) // +
+#define JP_ASTR LSFT(JP_COLN) // *
+#define JP_RCBR LSFT(JP_RBRC) // }
+#define JP_UNDS LSFT(JP_BSLS) // _
+
+
+// These symbols are correspond to US101-layout.
+#define JP_MINS KC_MINS // -
+#define JP_SCLN KC_SCLN // ;
+#define JP_COMM KC_COMM // ,
+#define JP_DOT  KC_DOT  // .
+#define JP_SLSH KC_SLSH // /
+// shifted
+#define JP_EXLM KC_EXLM // !
+#define JP_HASH KC_HASH // #
+#define JP_DLR  KC_DLR  // $
+#define JP_PERC KC_PERC // %
+#define JP_LT   KC_LT   // <
+#define JP_GT   KC_GT   // >
+#define JP_QUES KC_QUES // ?
+
+
+#endif
diff --git a/quantum/matrix.c b/quantum/matrix.c
index 3174e0739..07eb87bc3 100644
--- a/quantum/matrix.c
+++ b/quantum/matrix.c
@@ -25,37 +25,65 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "debug.h"
 #include "util.h"
 #include "matrix.h"
+#include "timer.h"
+
 
 /* Set 0 if debouncing isn't needed */
 
 #ifndef DEBOUNCING_DELAY
 #   define DEBOUNCING_DELAY 5
 #endif
-static uint8_t debouncing = DEBOUNCING_DELAY;
+
+#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)
+#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
+
+#ifdef MATRIX_MASKED
+    extern const matrix_row_t matrix_mask[];
+#endif
 
 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_raw[MATRIX_ROWS];
 static matrix_row_t matrix_debouncing[MATRIX_ROWS];
 
-#if DIODE_DIRECTION == ROW2COL
-    static matrix_row_t matrix_reversed[MATRIX_COLS];
-    static matrix_row_t matrix_reversed_debouncing[MATRIX_COLS];
-#endif
 
-#if MATRIX_COLS > 16
-    #define SHIFTER 1UL
-#else
-    #define SHIFTER 1
+#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);
+#else // 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 read_cols(void);
-static void init_cols(void);
-static void unselect_rows(void);
-static void select_row(uint8_t row);
-
 __attribute__ ((weak))
 void matrix_init_quantum(void) {
     matrix_init_kb();
@@ -95,7 +123,7 @@ uint8_t matrix_cols(void) {
 }
 
 // void matrix_power_up(void) {
-// #if DIODE_DIRECTION == COL2ROW
+// #if (DIODE_DIRECTION == COL2ROW)
 //     for (int8_t r = MATRIX_ROWS - 1; r >= 0; --r) {
 //         /* DDRxn */
 //         _SFR_IO8((row_pins[r] >> 4) + 1) |= _BV(row_pins[r] & 0xF);
@@ -119,19 +147,26 @@ uint8_t matrix_cols(void) {
 // }
 
 void matrix_init(void) {
+
     // To use PORTF disable JTAG with writing JTD bit twice within four cycles.
-    #ifdef __AVR_ATmega32U4__
+    #if  (defined(__AVR_AT90USB1286__) || defined(__AVR_AT90USB1287__) || defined(__AVR_ATmega32U4__))
         MCUCR |= _BV(JTD);
         MCUCR |= _BV(JTD);
     #endif
 
     // initialize row and col
+#if (DIODE_DIRECTION == COL2ROW)
     unselect_rows();
     init_cols();
+#else // ROW2COL
+    unselect_cols();
+    init_rows();
+#endif
 
     // initialize matrix state: all keys off
     for (uint8_t i=0; i < MATRIX_ROWS; i++) {
         matrix[i] = 0;
+        matrix_raw[i] = 0;
         matrix_debouncing[i] = 0;
     }
 
@@ -141,71 +176,60 @@ void matrix_init(void) {
 uint8_t matrix_scan(void)
 {
 
-#if DIODE_DIRECTION == COL2ROW
-    for (uint8_t i = 0; i < MATRIX_ROWS; i++) {
-        select_row(i);
-        wait_us(30);  // without this wait read unstable value.
-        matrix_row_t cols = read_cols();
-        if (matrix_debouncing[i] != cols) {
-            matrix_debouncing[i] = cols;
-            if (debouncing) {
-                debug("bounce!: "); debug_hex(debouncing); debug("\n");
-            }
-            debouncing = DEBOUNCING_DELAY;
-        }
-        unselect_rows();
-    }
+#if (DIODE_DIRECTION == COL2ROW)
 
-    if (debouncing) {
-        if (--debouncing) {
-            wait_ms(1);
-        } else {
-            for (uint8_t i = 0; i < MATRIX_ROWS; i++) {
-                matrix[i] = matrix_debouncing[i];
+    // 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
+
     }
-#else
-    for (uint8_t i = 0; i < MATRIX_COLS; i++) {
-        select_row(i);
-        wait_us(30);  // without this wait read unstable value.
-        matrix_row_t rows = read_cols();
-        if (matrix_reversed_debouncing[i] != rows) {
-            matrix_reversed_debouncing[i] = rows;
-            if (debouncing) {
-                debug("bounce!: "); debug_hex(debouncing); debug("\n");
+
+#else // 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();
             }
-            debouncing = DEBOUNCING_DELAY;
-        }
-        unselect_rows();
+#       else
+             read_rows_on_col(matrix, current_col);
+#       endif
+
     }
 
-    if (debouncing) {
-        if (--debouncing) {
-            wait_ms(1);
-        } else {
-            for (uint8_t i = 0; i < MATRIX_COLS; i++) {
-                matrix_reversed[i] = matrix_reversed_debouncing[i];
+#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;
         }
-    }
-    for (uint8_t y = 0; y < MATRIX_ROWS; y++) {
-        matrix_row_t row = 0;
-        for (uint8_t x = 0; x < MATRIX_COLS; x++) {
-            row |= ((matrix_reversed[x] & (1<<y)) >> y) << x;
-        }
-        matrix[y] = row;
-    }
-#endif
+#   endif
 
     matrix_scan_quantum();
-
     return 1;
 }
 
 bool matrix_is_modified(void)
 {
+#if (DEBOUNCING_DELAY > 0)
     if (debouncing) return false;
+#endif
     return true;
 }
 
@@ -218,15 +242,22 @@ bool matrix_is_on(uint8_t row, uint8_t col)
 inline
 matrix_row_t matrix_get_row(uint8_t row)
 {
+    // Matrix mask lets you disable switches in the returned matrix data. For example, if you have a
+    // switch blocker installed and the switch is always pressed.
+#ifdef MATRIX_MASKED
+    return matrix[row] & matrix_mask[row];
+#else
     return matrix[row];
+#endif
 }
 
 void matrix_print(void)
 {
-    print("\nr/c 0123456789ABCDEF\n");
+    print_matrix_header();
+
     for (uint8_t row = 0; row < MATRIX_ROWS; row++) {
         phex(row); print(": ");
-        pbin_reverse16(matrix_get_row(row));
+        print_matrix_row(row);
         print("\n");
     }
 }
@@ -235,63 +266,148 @@ uint8_t matrix_key_count(void)
 {
     uint8_t count = 0;
     for (uint8_t i = 0; i < MATRIX_ROWS; i++) {
-        count += bitpop16(matrix[i]);
+        count += matrix_bitpop(i);
     }
     return count;
 }
 
+
+
+#if (DIODE_DIRECTION == COL2ROW)
+
 static void init_cols(void)
 {
-#if DIODE_DIRECTION == COL2ROW
-    for(int x = 0; x < MATRIX_COLS; x++) {
-        int pin = col_pins[x];
-#else
-    for(int x = 0; x < MATRIX_ROWS; x++) {
-        int pin = row_pins[x];
-#endif
-        _SFR_IO8((pin >> 4) + 1) &=  ~_BV(pin & 0xF);
-        _SFR_IO8((pin >> 4) + 2) |= _BV(pin & 0xF);
+    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 matrix_row_t read_cols(void)
+static bool read_cols_on_row(matrix_row_t current_matrix[], uint8_t current_row)
 {
-    matrix_row_t result = 0;
+    // Store last value of row prior to reading
+    matrix_row_t last_row_value = current_matrix[current_row];
 
-#if DIODE_DIRECTION == COL2ROW
-    for(int x = 0; x < MATRIX_COLS; x++) {     
-        int pin = col_pins[x];
-#else
-    for(int x = 0; x < MATRIX_ROWS; x++) {
-        int pin = row_pins[x];
-#endif
-        result |= (_SFR_IO8(pin >> 4) & _BV(pin & 0xF)) ? 0 : (SHIFTER << x);
+    // 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);
     }
-    return result;
+
+    // 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)
 {
-#if DIODE_DIRECTION == COL2ROW
-    for(int x = 0; x < MATRIX_ROWS; x++) { 
-        int pin = row_pins[x];
-#else
-    for(int x = 0; x < MATRIX_COLS; x++) { 
-        int pin = col_pins[x];
-#endif
-        _SFR_IO8((pin >> 4) + 1) &=  ~_BV(pin & 0xF);
-        _SFR_IO8((pin >> 4) + 2) |= _BV(pin & 0xF);
+    for(uint8_t x = 0; x < MATRIX_ROWS; 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 void select_row(uint8_t row)
+#else // ROW2COL
+
+static void init_rows(void)
 {
+    for(uint8_t x = 0; x < MATRIX_ROWS; 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
+    }
+}
 
-#if DIODE_DIRECTION == COL2ROW
-    int pin = row_pins[row];
-#else
-    int pin = col_pins[row];
-#endif
-    _SFR_IO8((pin >> 4) + 1) |=  _BV(pin & 0xF);
-    _SFR_IO8((pin >> 4) + 2) &= ~_BV(pin & 0xF);
+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 < MATRIX_ROWS; 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
diff --git a/quantum/quantum.c b/quantum/quantum.c
index 098312e6e..b5e2d60b9 100644
--- a/quantum/quantum.c
+++ b/quantum/quantum.c
@@ -1,5 +1,9 @@
 #include "quantum.h"
 
+#ifndef TAPPING_TERM
+#define TAPPING_TERM 200
+#endif
+
 static void do_code16 (uint16_t code, void (*f) (uint8_t)) {
   switch (code) {
   case QK_MODS ... QK_MODS_MAX:
@@ -75,6 +79,7 @@ void reset_keyboard(void) {
 #endif
 
 static bool shift_interrupted[2] = {0, 0};
+static uint16_t scs_timer = 0;
 
 bool process_record_quantum(keyrecord_t *record) {
 
@@ -283,6 +288,7 @@ bool process_record_quantum(keyrecord_t *record) {
     case KC_LSPO: {
       if (record->event.pressed) {
         shift_interrupted[0] = false;
+        scs_timer = timer_read ();
         register_mods(MOD_BIT(KC_LSFT));
       }
       else {
@@ -292,7 +298,7 @@ bool process_record_quantum(keyrecord_t *record) {
             shift_interrupted[1] = true;
           }
         #endif
-        if (!shift_interrupted[0]) {
+        if (!shift_interrupted[0] && timer_elapsed(scs_timer) < TAPPING_TERM) {
           register_code(LSPO_KEY);
           unregister_code(LSPO_KEY);
         }
@@ -305,6 +311,7 @@ bool process_record_quantum(keyrecord_t *record) {
     case KC_RSPC: {
       if (record->event.pressed) {
         shift_interrupted[1] = false;
+        scs_timer = timer_read ();
         register_mods(MOD_BIT(KC_RSFT));
       }
       else {
@@ -314,7 +321,7 @@ bool process_record_quantum(keyrecord_t *record) {
             shift_interrupted[1] = true;
           }
         #endif
-        if (!shift_interrupted[1]) {
+        if (!shift_interrupted[1] && timer_elapsed(scs_timer) < TAPPING_TERM) {
           register_code(RSPC_KEY);
           unregister_code(RSPC_KEY);
         }
diff --git a/quantum/variable_trace.c b/quantum/variable_trace.c
new file mode 100644
index 000000000..de580244c
--- /dev/null
+++ b/quantum/variable_trace.c
@@ -0,0 +1,110 @@
+#include "variable_trace.h"
+#include <stddef.h>
+#include <string.h>
+
+#ifdef NO_PRINT
+#error "You need undef NO_PRINT to use the variable trace feature"
+#endif
+
+#ifndef CONSOLE_ENABLE
+#error "The console needs to be enabled in the makefile to use the variable trace feature"
+#endif
+
+
+#define NUM_TRACED_VARIABLES 1
+#ifndef MAX_VARIABLE_TRACE_SIZE
+    #define MAX_VARIABLE_TRACE_SIZE 4
+#endif
+
+typedef struct {
+    const char* name;
+    void* addr;
+    unsigned size;
+    const char* func;
+    int line;
+    uint8_t last_value[MAX_VARIABLE_TRACE_SIZE];
+
+} traced_variable_t;
+
+static traced_variable_t traced_variables[NUM_TRACED_VARIABLES];
+
+void add_traced_variable(const char* name, void* addr, unsigned size, const char* func, int line) {
+    verify_traced_variables(func, line);
+    if (size > MAX_VARIABLE_TRACE_SIZE) {
+#if defined(__AVR__)
+       xprintf("Traced variable \"%S\" exceeds the maximum size %d\n", name, size);
+#else
+       xprintf("Traced variable \"%s\" exceeds the maximum size %d\n", name, size);
+#endif
+       size = MAX_VARIABLE_TRACE_SIZE;
+    }
+    int index = -1;
+    for (int i = 0; i < NUM_TRACED_VARIABLES; i++) {
+        if (index == -1 && traced_variables[i].addr == NULL){
+            index = i;
+        }
+        else if (strcmp_P(name, traced_variables[i].name)==0) {
+            index = i;
+            break;
+        }
+    }
+
+    if (index == -1) {
+        xprintf("You can only trace %d variables at the same time\n", NUM_TRACED_VARIABLES);
+        return;
+    }
+
+    traced_variable_t* t = &traced_variables[index];
+    t->name = name;
+    t->addr = addr;
+    t->size = size;
+    t->func = func;
+    t->line = line;
+    memcpy(&t->last_value[0], addr, size);
+
+}
+
+void remove_traced_variable(const char* name, const char* func, int line) {
+    verify_traced_variables(func, line);
+    for (int i = 0; i < NUM_TRACED_VARIABLES; i++) {
+        if (strcmp_P(name, traced_variables[i].name)==0) {
+            traced_variables[i].name = 0;
+            traced_variables[i].addr = NULL;
+            break;
+        }
+    }
+}
+
+void verify_traced_variables(const char* func, int line) {
+    for (int i = 0; i < NUM_TRACED_VARIABLES; i++) {
+        traced_variable_t* t = &traced_variables[i];
+        if (t->addr != NULL && t->name != NULL) {
+            if (memcmp(t->last_value, t->addr, t->size)!=0){
+#if defined(__AVR__)
+               xprintf("Traced variable \"%S\" has been modified\n", t->name);
+               xprintf("Between %S:%d\n", t->func, t->line);
+               xprintf("And %S:%d\n", func, line);
+
+#else
+               xprintf("Traced variable \"%s\" has been modified\n", t->name);
+               xprintf("Between %s:%d\n", t->func, t->line);
+               xprintf("And %s:%d\n", func, line);
+#endif
+               xprintf("Previous value ");
+               for (int j=0; j<t->size;j++) {
+                   print_hex8(t->last_value[j]);
+               }
+               xprintf("\nNew value ");
+               uint8_t* addr = (uint8_t*)(t->addr);
+               for (int j=0; j<t->size;j++) {
+                   print_hex8(addr[j]);
+               }
+               xprintf("\n");
+               memcpy(t->last_value, addr, t->size);
+           }
+        }
+
+        t->func = func;
+        t->line = line;
+    }
+}
diff --git a/quantum/variable_trace.h b/quantum/variable_trace.h
new file mode 100644
index 000000000..46bd82786
--- /dev/null
+++ b/quantum/variable_trace.h
@@ -0,0 +1,34 @@
+#ifndef VARIABLE_TRACE_H
+#define VARIABLE_TRACE_H
+
+// For more information about the variable tracing see the readme.
+
+#include "print.h"
+
+#ifdef NUM_TRACED_VARIABLES
+
+// Start tracing a variable at the memory address addr
+// The name can be anything and is used only for reporting
+// The size should usually be the same size as the variable you are interested in
+#define ADD_TRACED_VARIABLE(name, addr, size) \
+    add_traced_variable(PSTR(name), (void*)addr, size, PSTR(__FILE__), __LINE__)
+
+// Stop tracing the variable with the given name
+#define REMOVE_TRACED_VARIABLE(name) remove_traced_variable(PSTR(name), PSTR(__FILE__), __LINE__)
+
+// Call to get messages when the variable has been changed
+#define VERIFY_TRACED_VARIABLES() verify_traced_variables(PSTR(__FILE__), __LINE__)
+
+#else
+
+#define ADD_TRACED_VARIABLE(name, addr, size)
+#define REMOVE_TRACED_VARIABLE(name)
+#define VERIFY_TRACED_VARIABLES()
+
+#endif
+
+// Don't call directly, use the macros instead
+void add_traced_variable(const char* name, void* addr, unsigned size, const char* func, int line);
+void remove_traced_variable(const char* name, const char* func, int line);
+void verify_traced_variables(const char* func, int line);
+#endif