15 files changed, 2057 insertions, 87 deletions

diff --git a/quantum/debounce/asym_eager_defer_pk.c b/quantum/debounce/asym_eager_defer_pk.c
new file mode 100644
index 0000000000..24380dc5e5
--- /dev/null
+++ b/quantum/debounce/asym_eager_defer_pk.c
@@ -0,0 +1,171 @@
+/*
+ * Copyright 2017 Alex Ong <the.onga@gmail.com>
+ * Copyright 2020 Andrei Purdea <andrei@purdea.ro>
+ * Copyright 2021 Simon Arlott
+ *
+ * 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/>.
+ */
+
+/*
+Basic symmetric per-key algorithm. Uses an 8-bit counter per key.
+When no state changes have occured for DEBOUNCE milliseconds, we push the state.
+*/
+
+#include "matrix.h"
+#include "timer.h"
+#include "quantum.h"
+#include <stdlib.h>
+
+#ifdef PROTOCOL_CHIBIOS
+#    if CH_CFG_USE_MEMCORE == FALSE
+#        error ChibiOS is configured without a memory allocator. Your keyboard may have set `#define CH_CFG_USE_MEMCORE FALSE`, which is incompatible with this debounce algorithm.
+#    endif
+#endif
+
+#ifndef DEBOUNCE
+#    define DEBOUNCE 5
+#endif
+
+// Maximum debounce: 127ms
+#if DEBOUNCE > 127
+#    undef DEBOUNCE
+#    define DEBOUNCE 127
+#endif
+
+#define ROW_SHIFTER ((matrix_row_t)1)
+
+typedef struct {
+    bool pressed : 1;
+    uint8_t time : 7;
+} debounce_counter_t;
+
+#if DEBOUNCE > 0
+static debounce_counter_t *debounce_counters;
+static fast_timer_t last_time;
+static bool counters_need_update;
+static bool matrix_need_update;
+
+#define DEBOUNCE_ELAPSED 0
+
+static void update_debounce_counters_and_transfer_if_expired(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t elapsed_time);
+static void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows);
+
+// we use num_rows rather than MATRIX_ROWS to support split keyboards
+void debounce_init(uint8_t num_rows) {
+    debounce_counters = malloc(num_rows * MATRIX_COLS * sizeof(debounce_counter_t));
+    int i = 0;
+    for (uint8_t r = 0; r < num_rows; r++) {
+        for (uint8_t c = 0; c < MATRIX_COLS; c++) {
+            debounce_counters[i++].time = DEBOUNCE_ELAPSED;
+        }
+    }
+}
+
+void debounce_free(void) {
+    free(debounce_counters);
+    debounce_counters = NULL;
+}
+
+void debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed) {
+    bool updated_last = false;
+
+    if (counters_need_update) {
+        fast_timer_t now = timer_read_fast();
+        fast_timer_t elapsed_time = TIMER_DIFF_FAST(now, last_time);
+
+        last_time = now;
+        updated_last = true;
+        if (elapsed_time > UINT8_MAX) {
+            elapsed_time = UINT8_MAX;
+        }
+
+        if (elapsed_time > 0) {
+            update_debounce_counters_and_transfer_if_expired(raw, cooked, num_rows, elapsed_time);
+        }
+    }
+
+    if (changed || matrix_need_update) {
+        if (!updated_last) {
+            last_time = timer_read_fast();
+        }
+
+        transfer_matrix_values(raw, cooked, num_rows);
+    }
+}
+
+static void update_debounce_counters_and_transfer_if_expired(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t elapsed_time) {
+    debounce_counter_t *debounce_pointer = debounce_counters;
+
+    counters_need_update = false;
+    matrix_need_update = false;
+
+    for (uint8_t row = 0; row < num_rows; row++) {
+        for (uint8_t col = 0; col < MATRIX_COLS; col++) {
+            matrix_row_t col_mask = (ROW_SHIFTER << col);
+
+            if (debounce_pointer->time != DEBOUNCE_ELAPSED) {
+                if (debounce_pointer->time <= elapsed_time) {
+                    debounce_pointer->time = DEBOUNCE_ELAPSED;
+
+                    if (debounce_pointer->pressed) {
+                        // key-down: eager
+                        matrix_need_update = true;
+                    } else {
+                        // key-up: defer
+                        cooked[row] = (cooked[row] & ~col_mask) | (raw[row] & col_mask);
+                    }
+                } else {
+                    debounce_pointer->time -= elapsed_time;
+                    counters_need_update = true;
+                }
+            }
+            debounce_pointer++;
+        }
+    }
+}
+
+static void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows) {
+    debounce_counter_t *debounce_pointer = debounce_counters;
+
+    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++) {
+            matrix_row_t col_mask = (ROW_SHIFTER << col);
+
+            if (delta & col_mask) {
+                if (debounce_pointer->time == DEBOUNCE_ELAPSED) {
+                    debounce_pointer->pressed = (raw[row] & col_mask);
+                    debounce_pointer->time = DEBOUNCE;
+                    counters_need_update = true;
+
+                    if (debounce_pointer->pressed) {
+                        // key-down: eager
+                        cooked[row] ^= col_mask;
+                    }
+                }
+            } else if (debounce_pointer->time != DEBOUNCE_ELAPSED) {
+                if (!debounce_pointer->pressed) {
+                    // key-up: defer
+                    debounce_pointer->time = DEBOUNCE_ELAPSED;
+                }
+            }
+            debounce_pointer++;
+        }
+    }
+}
+
+bool debounce_active(void) { return true; }
+#else
+#    include "none.c"
+#endif
diff --git a/quantum/debounce/none.c b/quantum/debounce/none.c
new file mode 100644
index 0000000000..b03892bc5b
--- /dev/null
+++ b/quantum/debounce/none.c
@@ -0,0 +1,31 @@
+/* Copyright 2021 Simon Arlott
+ *
+ * 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/>.
+ */
+
+#include "matrix.h"
+#include "quantum.h"
+#include <stdlib.h>
+
+void debounce_init(uint8_t num_rows) {}
+
+void debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed) {
+    for (int i = 0; i < num_rows; i++) {
+        cooked[i] = raw[i];
+    }
+}
+
+bool debounce_active(void) { return false; }
+
+void debounce_free(void) {}
diff --git a/quantum/debounce/sym_defer_g.c b/quantum/debounce/sym_defer_g.c
index 3ed9055d2a..fbefd55ede 100644
--- a/quantum/debounce/sym_defer_g.c
+++ b/quantum/debounce/sym_defer_g.c
@@ -1,5 +1,6 @@
 /*
 Copyright 2017 Alex Ong<the.onga@gmail.com>
+Copyright 2021 Simon Arlott
 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
@@ -23,30 +24,29 @@ When no state changes have occured for DEBOUNCE milliseconds, we push the state.
 #    define DEBOUNCE 5
 #endif
 
-void        debounce_init(uint8_t num_rows) {}
+#if DEBOUNCE > 0
 static bool debouncing = false;
+static fast_timer_t debouncing_time;
 
-#if DEBOUNCE > 0
-static uint16_t debouncing_time;
-void            debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed) {
+void debounce_init(uint8_t num_rows) {}
+
+void debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed) {
     if (changed) {
         debouncing      = true;
-        debouncing_time = timer_read();
+        debouncing_time = timer_read_fast();
     }
 
-    if (debouncing && timer_elapsed(debouncing_time) > DEBOUNCE) {
+    if (debouncing && timer_elapsed_fast(debouncing_time) >= DEBOUNCE) {
         for (int i = 0; i < num_rows; i++) {
             cooked[i] = raw[i];
         }
         debouncing = false;
     }
 }
-#else  // no debouncing.
-void debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed) {
-    for (int i = 0; i < num_rows; i++) {
-        cooked[i] = raw[i];
-    }
-}
-#endif
 
 bool debounce_active(void) { return debouncing; }
+
+void debounce_free(void) {}
+#else  // no debouncing.
+#    include "none.c"
+#endif
diff --git a/quantum/debounce/sym_defer_pk.c b/quantum/debounce/sym_defer_pk.c
index 60513f98e1..626a9be841 100644
--- a/quantum/debounce/sym_defer_pk.c
+++ b/quantum/debounce/sym_defer_pk.c
@@ -1,6 +1,7 @@
 /*
 Copyright 2017 Alex Ong<the.onga@gmail.com>
 Copyright 2020 Andrei Purdea<andrei@purdea.ro>
+Copyright 2021 Simon Arlott
 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
@@ -33,28 +34,25 @@ When no state changes have occured for DEBOUNCE milliseconds, we push the state.
 #    define DEBOUNCE 5
 #endif
 
+// Maximum debounce: 255ms
+#if DEBOUNCE > UINT8_MAX
+#    undef DEBOUNCE
+#    define DEBOUNCE UINT8_MAX
+#endif
+
 #define ROW_SHIFTER ((matrix_row_t)1)
 
-#define debounce_counter_t uint8_t
+typedef uint8_t debounce_counter_t;
 
+#if DEBOUNCE > 0
 static debounce_counter_t *debounce_counters;
+static fast_timer_t        last_time;
 static bool                counters_need_update;
 
-#define DEBOUNCE_ELAPSED 251
-#define MAX_DEBOUNCE (DEBOUNCE_ELAPSED - 1)
-
-static uint8_t wrapping_timer_read(void) {
-    static uint16_t time        = 0;
-    static uint8_t  last_result = 0;
-    uint16_t        new_time    = timer_read();
-    uint16_t        diff        = new_time - time;
-    time                        = new_time;
-    last_result                 = (last_result + diff) % (MAX_DEBOUNCE + 1);
-    return last_result;
-}
+#define DEBOUNCE_ELAPSED 0
 
-void update_debounce_counters_and_transfer_if_expired(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t current_time);
-void start_debounce_counters(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t current_time);
+static void update_debounce_counters_and_transfer_if_expired(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t elapsed_time);
+static void start_debounce_counters(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows);
 
 // we use num_rows rather than MATRIX_ROWS to support split keyboards
 void debounce_init(uint8_t num_rows) {
@@ -67,27 +65,49 @@ void debounce_init(uint8_t num_rows) {
     }
 }
 
+void debounce_free(void) {
+    free(debounce_counters);
+    debounce_counters = NULL;
+}
+
 void debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed) {
-    uint8_t current_time = wrapping_timer_read();
+    bool updated_last = false;
+
     if (counters_need_update) {
-        update_debounce_counters_and_transfer_if_expired(raw, cooked, num_rows, current_time);
+        fast_timer_t now = timer_read_fast();
+        fast_timer_t elapsed_time = TIMER_DIFF_FAST(now, last_time);
+
+        last_time = now;
+        updated_last = true;
+        if (elapsed_time > UINT8_MAX) {
+            elapsed_time = UINT8_MAX;
+        }
+
+        if (elapsed_time > 0) {
+            update_debounce_counters_and_transfer_if_expired(raw, cooked, num_rows, elapsed_time);
+        }
     }
 
     if (changed) {
-        start_debounce_counters(raw, cooked, num_rows, current_time);
+        if (!updated_last) {
+            last_time = timer_read_fast();
+        }
+
+        start_debounce_counters(raw, cooked, num_rows);
     }
 }
 
-void update_debounce_counters_and_transfer_if_expired(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t current_time) {
+static void update_debounce_counters_and_transfer_if_expired(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t elapsed_time) {
     counters_need_update                 = false;
     debounce_counter_t *debounce_pointer = debounce_counters;
     for (uint8_t row = 0; row < num_rows; row++) {
         for (uint8_t col = 0; col < MATRIX_COLS; col++) {
             if (*debounce_pointer != DEBOUNCE_ELAPSED) {
-                if (TIMER_DIFF(current_time, *debounce_pointer, MAX_DEBOUNCE) >= DEBOUNCE) {
+                if (*debounce_pointer <= elapsed_time) {
                     *debounce_pointer = DEBOUNCE_ELAPSED;
                     cooked[row]       = (cooked[row] & ~(ROW_SHIFTER << col)) | (raw[row] & (ROW_SHIFTER << col));
                 } else {
+                    *debounce_pointer -= elapsed_time;
                     counters_need_update = true;
                 }
             }
@@ -96,14 +116,14 @@ void update_debounce_counters_and_transfer_if_expired(matrix_row_t raw[], matrix
     }
 }
 
-void start_debounce_counters(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t current_time) {
+static void start_debounce_counters(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows) {
     debounce_counter_t *debounce_pointer = debounce_counters;
     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 (delta & (ROW_SHIFTER << col)) {
                 if (*debounce_pointer == DEBOUNCE_ELAPSED) {
-                    *debounce_pointer    = current_time;
+                    *debounce_pointer    = DEBOUNCE;
                     counters_need_update = true;
                 }
             } else {
@@ -115,3 +135,6 @@ void start_debounce_counters(matrix_row_t raw[], matrix_row_t cooked[], uint8_t
 }
 
 bool debounce_active(void) { return true; }
+#else
+#    include "none.c"
+#endif
diff --git a/quantum/debounce/sym_eager_pk.c b/quantum/debounce/sym_eager_pk.c
index e66cf92d79..15a3242e68 100644
--- a/quantum/debounce/sym_eager_pk.c
+++ b/quantum/debounce/sym_eager_pk.c
@@ -1,5 +1,6 @@
 /*
 Copyright 2017 Alex Ong<the.onga@gmail.com>
+Copyright 2021 Simon Arlott
 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
@@ -33,29 +34,26 @@ No further inputs are accepted until DEBOUNCE milliseconds have occurred.
 #    define DEBOUNCE 5
 #endif
 
+// Maximum debounce: 255ms
+#if DEBOUNCE > UINT8_MAX
+#    undef DEBOUNCE
+#    define DEBOUNCE UINT8_MAX
+#endif
+
 #define ROW_SHIFTER ((matrix_row_t)1)
 
-#define debounce_counter_t uint8_t
+typedef uint8_t debounce_counter_t;
 
+#if DEBOUNCE > 0
 static debounce_counter_t *debounce_counters;
+static fast_timer_t        last_time;
 static bool                counters_need_update;
 static bool                matrix_need_update;
 
-#define DEBOUNCE_ELAPSED 251
-#define MAX_DEBOUNCE (DEBOUNCE_ELAPSED - 1)
-
-static uint8_t wrapping_timer_read(void) {
-    static uint16_t time        = 0;
-    static uint8_t  last_result = 0;
-    uint16_t        new_time    = timer_read();
-    uint16_t        diff        = new_time - time;
-    time                        = new_time;
-    last_result                 = (last_result + diff) % (MAX_DEBOUNCE + 1);
-    return last_result;
-}
+#define DEBOUNCE_ELAPSED 0
 
-void update_debounce_counters(uint8_t num_rows, uint8_t current_time);
-void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t current_time);
+static void update_debounce_counters(uint8_t num_rows, uint8_t elapsed_time);
+static void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows);
 
 // we use num_rows rather than MATRIX_ROWS to support split keyboards
 void debounce_init(uint8_t num_rows) {
@@ -68,27 +66,51 @@ void debounce_init(uint8_t num_rows) {
     }
 }
 
+void debounce_free(void) {
+    free(debounce_counters);
+    debounce_counters = NULL;
+}
+
 void debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed) {
-    uint8_t current_time = wrapping_timer_read();
+    bool updated_last = false;
+
     if (counters_need_update) {
-        update_debounce_counters(num_rows, current_time);
+        fast_timer_t now = timer_read_fast();
+        fast_timer_t elapsed_time = TIMER_DIFF_FAST(now, last_time);
+
+        last_time = now;
+        updated_last = true;
+        if (elapsed_time > UINT8_MAX) {
+            elapsed_time = UINT8_MAX;
+        }
+
+        if (elapsed_time > 0) {
+            update_debounce_counters(num_rows, elapsed_time);
+        }
     }
 
     if (changed || matrix_need_update) {
-        transfer_matrix_values(raw, cooked, num_rows, current_time);
+        if (!updated_last) {
+            last_time = timer_read_fast();
+        }
+
+        transfer_matrix_values(raw, cooked, num_rows);
     }
 }
 
 // If the current time is > debounce counter, set the counter to enable input.
-void update_debounce_counters(uint8_t num_rows, uint8_t current_time) {
+static void update_debounce_counters(uint8_t num_rows, uint8_t elapsed_time) {
     counters_need_update                 = false;
+    matrix_need_update                   = false;
     debounce_counter_t *debounce_pointer = debounce_counters;
     for (uint8_t row = 0; row < num_rows; row++) {
         for (uint8_t col = 0; col < MATRIX_COLS; col++) {
             if (*debounce_pointer != DEBOUNCE_ELAPSED) {
-                if (TIMER_DIFF(current_time, *debounce_pointer, MAX_DEBOUNCE) >= DEBOUNCE) {
+                if (*debounce_pointer <= elapsed_time) {
                     *debounce_pointer = DEBOUNCE_ELAPSED;
+                    matrix_need_update = true;
                 } else {
+                    *debounce_pointer -= elapsed_time;
                     counters_need_update = true;
                 }
             }
@@ -98,8 +120,7 @@ void update_debounce_counters(uint8_t num_rows, uint8_t current_time) {
 }
 
 // upload from raw_matrix to final matrix;
-void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t current_time) {
-    matrix_need_update                   = false;
+static void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows) {
     debounce_counter_t *debounce_pointer = debounce_counters;
     for (uint8_t row = 0; row < num_rows; row++) {
         matrix_row_t delta        = raw[row] ^ cooked[row];
@@ -108,11 +129,9 @@ void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t n
             matrix_row_t col_mask = (ROW_SHIFTER << col);
             if (delta & col_mask) {
                 if (*debounce_pointer == DEBOUNCE_ELAPSED) {
-                    *debounce_pointer    = current_time;
+                    *debounce_pointer    = DEBOUNCE;
                     counters_need_update = true;
                     existing_row ^= col_mask;  // flip the bit.
-                } else {
-                    matrix_need_update = true;
                 }
             }
             debounce_pointer++;
@@ -122,3 +141,6 @@ void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t n
 }
 
 bool debounce_active(void) { return true; }
+#else
+#    include "none.c"
+#endif
diff --git a/quantum/debounce/sym_eager_pr.c b/quantum/debounce/sym_eager_pr.c
index 20ccb46f1d..2ad592c5a6 100644
--- a/quantum/debounce/sym_eager_pr.c
+++ b/quantum/debounce/sym_eager_pr.c
@@ -1,5 +1,6 @@
 /*
 Copyright 2019 Alex Ong<the.onga@gmail.com>
+Copyright 2021 Simon Arlott
 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
@@ -33,27 +34,25 @@ No further inputs are accepted until DEBOUNCE milliseconds have occurred.
 #    define DEBOUNCE 5
 #endif
 
-#define debounce_counter_t uint8_t
+// Maximum debounce: 255ms
+#if DEBOUNCE > UINT8_MAX
+#    undef DEBOUNCE
+#    define DEBOUNCE UINT8_MAX
+#endif
+
+typedef uint8_t debounce_counter_t;
+
+#if DEBOUNCE > 0
 static bool matrix_need_update;
 
 static debounce_counter_t *debounce_counters;
+static fast_timer_t        last_time;
 static bool                counters_need_update;
 
-#define DEBOUNCE_ELAPSED 251
-#define MAX_DEBOUNCE (DEBOUNCE_ELAPSED - 1)
-
-static uint8_t wrapping_timer_read(void) {
-    static uint16_t time        = 0;
-    static uint8_t  last_result = 0;
-    uint16_t        new_time    = timer_read();
-    uint16_t        diff        = new_time - time;
-    time                        = new_time;
-    last_result                 = (last_result + diff) % (MAX_DEBOUNCE + 1);
-    return last_result;
-}
+#define DEBOUNCE_ELAPSED 0
 
-void update_debounce_counters(uint8_t num_rows, uint8_t current_time);
-void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t current_time);
+static void update_debounce_counters(uint8_t num_rows, uint8_t elapsed_time);
+static void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows);
 
 // we use num_rows rather than MATRIX_ROWS to support split keyboards
 void debounce_init(uint8_t num_rows) {
@@ -63,27 +62,50 @@ void debounce_init(uint8_t num_rows) {
     }
 }
 
+void debounce_free(void) {
+    free(debounce_counters);
+    debounce_counters = NULL;
+}
+
 void debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed) {
-    uint8_t current_time  = wrapping_timer_read();
-    bool    needed_update = counters_need_update;
+    bool updated_last = false;
+
     if (counters_need_update) {
-        update_debounce_counters(num_rows, current_time);
+        fast_timer_t now = timer_read_fast();
+        fast_timer_t elapsed_time = TIMER_DIFF_FAST(now, last_time);
+
+        last_time = now;
+        updated_last = true;
+        if (elapsed_time > UINT8_MAX) {
+            elapsed_time = UINT8_MAX;
+        }
+
+        if (elapsed_time > 0) {
+            update_debounce_counters(num_rows, elapsed_time);
+        }
     }
 
-    if (changed || (needed_update && !counters_need_update) || matrix_need_update) {
-        transfer_matrix_values(raw, cooked, num_rows, current_time);
+    if (changed || matrix_need_update) {
+        if (!updated_last) {
+            last_time = timer_read_fast();
+        }
+
+        transfer_matrix_values(raw, cooked, num_rows);
     }
 }
 
 // If the current time is > debounce counter, set the counter to enable input.
-void update_debounce_counters(uint8_t num_rows, uint8_t current_time) {
+static void update_debounce_counters(uint8_t num_rows, uint8_t elapsed_time) {
     counters_need_update                 = false;
+    matrix_need_update                   = false;
     debounce_counter_t *debounce_pointer = debounce_counters;
     for (uint8_t row = 0; row < num_rows; row++) {
         if (*debounce_pointer != DEBOUNCE_ELAPSED) {
-            if (TIMER_DIFF(current_time, *debounce_pointer, MAX_DEBOUNCE) >= DEBOUNCE) {
+            if (*debounce_pointer <= elapsed_time) {
                 *debounce_pointer = DEBOUNCE_ELAPSED;
+                matrix_need_update = true;
             } else {
+                *debounce_pointer -= elapsed_time;
                 counters_need_update = true;
             }
         }
@@ -92,8 +114,7 @@ void update_debounce_counters(uint8_t num_rows, uint8_t current_time) {
 }
 
 // upload from raw_matrix to final matrix;
-void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, uint8_t current_time) {
-    matrix_need_update                   = false;
+static void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows) {
     debounce_counter_t *debounce_pointer = debounce_counters;
     for (uint8_t row = 0; row < num_rows; row++) {
         matrix_row_t existing_row = cooked[row];
@@ -102,11 +123,9 @@ void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t n
         // determine new value basd on debounce pointer + raw value
         if (existing_row != raw_row) {
             if (*debounce_pointer == DEBOUNCE_ELAPSED) {
-                *debounce_pointer    = current_time;
+                *debounce_pointer    = DEBOUNCE;
                 cooked[row]          = raw_row;
                 counters_need_update = true;
-            } else {
-                matrix_need_update = true;
             }
         }
         debounce_pointer++;
@@ -114,3 +133,6 @@ void transfer_matrix_values(matrix_row_t raw[], matrix_row_t cooked[], uint8_t n
 }
 
 bool debounce_active(void) { return true; }
+#else
+#    include "none.c"
+#endif
diff --git a/quantum/debounce/tests/asym_eager_defer_pk_tests.cpp b/quantum/debounce/tests/asym_eager_defer_pk_tests.cpp
new file mode 100644
index 0000000000..fe374c3dfa
--- /dev/null
+++ b/quantum/debounce/tests/asym_eager_defer_pk_tests.cpp
@@ -0,0 +1,374 @@
+/* Copyright 2021 Simon Arlott
+ *
+ * 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/>.
+ */
+
+#include "gtest/gtest.h"
+
+#include "debounce_test_common.h"
+
+TEST_F(DebounceTest, OneKeyShort1) {
+    addEvents({ /* Time, Inputs, Outputs */
+        {0, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+        /* Release key after 1ms delay */
+        {1, {{0, 1, UP}}, {}},
+
+        /*
+         * Until the eager timer on DOWN is observed to finish, the defer timer
+         * on UP can't start. There's no workaround for this because it's not
+         * possible to debounce an event that isn't being tracked.
+         *
+         * sym_defer_pk has the same problem but the test has to track that the
+         * key changed state so the DOWN timer is always allowed to finish
+         * before starting the UP timer.
+         */
+        {5, {}, {}},
+
+        {10, {}, {{0, 1, UP}}}, /* 5ms+5ms after DOWN at time 0 */
+        /* Press key again after 1ms delay */
+        {11, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+    });
+    runEvents();
+}
+
+TEST_F(DebounceTest, OneKeyShort2) {
+    addEvents({ /* Time, Inputs, Outputs */
+        {0, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+        /* Release key after 2ms delay */
+        {2, {{0, 1, UP}}, {}},
+
+        {5, {}, {}}, /* See OneKeyShort1 */
+
+        {10, {}, {{0, 1, UP}}}, /* 5ms+5ms after DOWN at time 0 */
+        /* Press key again after 1ms delay */
+        {11, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+    });
+    runEvents();
+}
+
+TEST_F(DebounceTest, OneKeyShort3) {
+    addEvents({ /* Time, Inputs, Outputs */
+        {0, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+        /* Release key after 3ms delay */
+        {3, {{0, 1, UP}}, {}},
+
+        {5, {}, {}}, /* See OneKeyShort1 */
+
+        {10, {}, {{0, 1, UP}}}, /* 5ms+5ms after DOWN at time 0 */
+        /* Press key again after 1ms delay */
+        {11, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+    });
+    runEvents();
+}
+
+TEST_F(DebounceTest, OneKeyShort4) {
+    addEvents({ /* Time, Inputs, Outputs */
+        {0, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+        /* Release key after 4ms delay */
+        {4, {{0, 1, UP}}, {}},
+
+        {5, {}, {}}, /* See OneKeyShort1 */
+
+        {10, {}, {{0, 1, UP}}}, /* 5ms+5ms after DOWN at time 0 */
+        /* Press key again after 1ms delay */
+        {11, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+    });
+    runEvents();
+}
+
+TEST_F(DebounceTest, OneKeyShort5) {
+    addEvents({ /* Time, Inputs, Outputs */
+        {0, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+
+        /* Release key after 5ms delay */
+        {5, {{0, 1, UP}}, {}},
+
+        {10, {}, {{0, 1, UP}}}, /* 5ms+5ms after DOWN at time 0 */
+        /* Press key again after 1ms delay */
+        {11, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+    });
+    runEvents();
+}
+
+TEST_F(DebounceTest, OneKeyShort6) {
+    addEvents({ /* Time, Inputs, Outputs */
+        {0, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+
+        /* Release key after 6ms delay */
+        {6, {{0, 1, UP}}, {}},
+
+        {11, {}, {{0, 1, UP}}}, /* 5ms after UP at time 6 */
+        /* Press key again after 1ms delay */
+        {12, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+    });
+    runEvents();
+}
+
+TEST_F(DebounceTest, OneKeyShort7) {
+    addEvents({ /* Time, Inputs, Outputs */
+        {0, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+
+        /* Release key after 7ms delay */
+        {7, {{0, 1, UP}}, {}},
+
+        {12, {}, {{0, 1, UP}}}, /* 5ms after UP at time 7 */
+        /* Press key again after 1ms delay */
+        {13, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+    });
+    runEvents();
+}
+
+TEST_F(DebounceTest, OneKeyShort8) {
+    addEvents({ /* Time, Inputs, Outputs */
+        {0, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+        /* Release key after 1ms delay */
+        {1, {{0, 1, UP}}, {}},
+
+        {5, {}, {}}, /* See OneKeyShort1 */
+
+        {10, {}, {{0, 1, UP}}}, /* 5ms after UP at time 7 */
+        /* Press key again after 0ms delay (scan 2) */
+        {10, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+    });
+    runEvents();
+}
+
+TEST_F(DebounceTest, OneKeyShort9) {
+    addEvents({ /* Time, Inputs, Outputs */
+        {0, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+        /* Release key after 1ms delay */
+        {1, {{0, 1, UP}}, {}},
+
+        {5, {}, {}}, /* See OneKeyShort1 */
+
+        /* Press key again after 0ms delay (same scan) before debounce finishes */
+        {10, {{0, 1, DOWN}}, {}},
+    });
+    runEvents();
+}
+
+TEST_F(DebounceTest, OneKeyBouncing1) {
+    addEvents({ /* Time, Inputs, Outputs */
+        {0, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+        {1, {{0, 1, UP}}, {}},
+        {2, {{0, 1, DOWN}}, {}},
+        {3, {{0, 1, UP}}, {}},
+        {4, {{0, 1, DOWN}}, {}},
+        {5, {{0, 1, UP}}, {}},
+        {6, {{0, 1, DOWN}}, {}},
+        {7, {{0, 1, UP}}, {}},
+        {8, {{0, 1, DOWN}}, {}},
+        {9, {{0, 1, UP}}, {}},
+        {10, {{0, 1, DOWN}}, {}},
+        {11, {{0, 1, UP}}, {}},
+        {12, {{0, 1, DOWN}}, {}},
+        {13, {{0, 1, UP}}, {}},
+        {14, {{0, 1, DOWN}}, {}},
+        {15, {{0, 1, UP}}, {}},
+
+        {20, {}, {{0, 1, UP}}},
+        /* Press key again after 1ms delay */
+        {21, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+    });
+    runEvents();
+}
+
+TEST_F(DebounceTest, OneKeyBouncing2) {
+    addEvents({ /* Time, Inputs, Outputs */
+        {0, {{0, 1, DOWN}}, {{0, 1, DOWN}}},
+        /* Change twice in the same time period */
+        {1, {{0, 1, UP}}, {}},
+        {1, {{0, 1, DOWN}}, {}},
+        /* Change three times in the same time period */
+        {2, {{0, 1, UP}}, {}},
+        {2, {{0, 1, DOWN}}, {}},
+        {2, {{0, 1, UP}}, {}},
+        /* Change twice in the same time period */
+        {6, {{0, 1, DOWN}}, {}},
+        {6, {{0, 1, UP}}, {}},
+        /* Change three times in the same time period */
+        {7, {{0, 1, DOWN}}, {}},
+        {7, {{0, 1, UP}}, {}},
+        {7, {{0, 1, DOWN}}, {}},
+        /* Change twice in the same time period */
+        {8, {{0, 1, UP}}, {}},
+        {8, {{0, 1, DOWN}}, {}},
+        /* Change three times in the same time period */
+        {9, {{0, 1, UP}}, {}},
+        {9, {{0, 1, DOWN}}, {}},</