Avoid 8-bit timer overflows in debounce algorithms (#12240)

* Add fast_timer_t that is 16-bit or 32-bit based on architecture

A 16-bit timer will overflow sooner but be faster to compare on AVR.

* Avoid 8-bit timer overflows in debounce algorithms

Count down remaining elapsed time instead of trying to do 8-bit timer
comparisons.

Add a "none" implementation that is automatically used if DEBOUNCE is
0 otherwise it will break the _pk/_pr count down.

* Avoid unnecessary polling of the entire matrix in sym_eager_pk

The matrix only needs to be updated when a debounce timer expires.

* Avoid unnecessary polling of the entire matrix in sym_eager_pr

The matrix only needs to be updated when a debounce timer expires.

The use of the "needed_update" variable is trying to do what
"matrix_need_update" was added to fix but didn't work because it only
applied when all keys finished debouncing.

* Fix sym_defer_g timing inconsistency compared to other debounce algorithms

DEBOUNCE=5 should process the key after 5ms, not 6ms

* Add debounce tests

4 files changed, 77 insertions, 4 deletions

diff --git a/tmk_core/common/arm_atsam/_timer.h b/tmk_core/common/arm_atsam/_timer.h
new file mode 100644
index 000000000..77402b612
--- /dev/null
+++ b/tmk_core/common/arm_atsam/_timer.h
@@ -0,0 +1,19 @@
+/* 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/>.
+ */
+#pragma once
+
+// The platform is 32-bit, so prefer 32-bit timers to avoid overflow
+#define FAST_TIMER_T_SIZE 32
diff --git a/tmk_core/common/avr/_timer.h b/tmk_core/common/avr/_timer.h
new file mode 100644
index 000000000..b81e0f68b
--- /dev/null
+++ b/tmk_core/common/avr/_timer.h
@@ -0,0 +1,19 @@
+/* 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/>.
+ */
+#pragma once
+
+// The platform is 8-bit, so prefer 16-bit timers to reduce code size
+#define FAST_TIMER_T_SIZE 16
diff --git a/tmk_core/common/chibios/_timer.h b/tmk_core/common/chibios/_timer.h
new file mode 100644
index 000000000..77402b612
--- /dev/null
+++ b/tmk_core/common/chibios/_timer.h
@@ -0,0 +1,19 @@
+/* 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/>.
+ */
+#pragma once
+
+// The platform is 32-bit, so prefer 32-bit timers to avoid overflow
+#define FAST_TIMER_T_SIZE 32
diff --git a/tmk_core/common/timer.h b/tmk_core/common/timer.h
index 58f637dd9..928811a2b 100644
--- a/tmk_core/common/timer.h
+++ b/tmk_core/common/timer.h
@@ -1,5 +1,6 @@
 /*
 Copyright 2011 Jun Wako <wakojun@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
@@ -17,13 +18,13 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #pragma once
 
+#if __has_include_next("_timer.h")
+#    include_next "_timer.h" /* Include the platform's _timer.h */
+#endif
+
 #include <stdint.h>
 #include <stdbool.h>
 
-#if defined(__AVR__)
-#    include "avr/timer_avr.h"
-#endif
-
 #define TIMER_DIFF(a, b, max) ((max == UINT8_MAX) ? ((uint8_t)((a) - (b))) : ((max == UINT16_MAX) ? ((uint16_t)((a) - (b))) : ((max == UINT32_MAX) ? ((uint32_t)((a) - (b))) : ((a) >= (b) ? (a) - (b) : (max) + 1 - (b) + (a)))))
 #define TIMER_DIFF_8(a, b) TIMER_DIFF(a, b, UINT8_MAX)
 #define TIMER_DIFF_16(a, b) TIMER_DIFF(a, b, UINT16_MAX)
@@ -47,6 +48,21 @@ uint32_t timer_elapsed32(uint32_t last);
 #define timer_expired(current, future) ((uint16_t)(current - future) < UINT16_MAX / 2)
 #define timer_expired32(current, future) ((uint32_t)(current - future) < UINT32_MAX / 2)
 
+// Use an appropriate timer integer size based on architecture (16-bit will overflow sooner)
+#if FAST_TIMER_T_SIZE < 32
+#    define TIMER_DIFF_FAST(a, b) TIMER_DIFF_16(a, b)
+#    define timer_expired_fast(current, future) timer_expired(current, future)
+typedef uint16_t fast_timer_t;
+fast_timer_t inline timer_read_fast(void) { return timer_read(); }
+fast_timer_t inline timer_elapsed_fast(fast_timer_t last) { return timer_elapsed(last); }
+#else
+#    define TIMER_DIFF_FAST(a, b) TIMER_DIFF_32(a, b)
+#    define timer_expired_fast(current, future) timer_expired32(current, future)
+typedef uint32_t fast_timer_t;
+fast_timer_t inline timer_read_fast(void) { return timer_read32(); }
+fast_timer_t inline timer_elapsed_fast(fast_timer_t last) { return timer_elapsed32(last); }
+#endif
+
 #ifdef __cplusplus
 }
 #endif