2020 November 28 Breaking Changes Update (#11053)

* Branch point for 2020 November 28 Breaking Change                                                

* Remove matrix_col_t to allow MATRIX_ROWS > 32 (#10183)                                           

* Add support for soft serial to ATmega32U2 (#10204)                                               

* Change MIDI velocity implementation to allow direct control of velocity value (#9940)            

* Add ability to build a subset of all keyboards based on platform.                                

* Actually use eeprom_driver_init().                                                               

* Make bootloader_jump weak for ChibiOS. (#10417)                                                  

* Joystick 16-bit support (#10439)                                                                 

* Per-encoder resolutions (#10259)                                                                 

* Share button state from mousekey to pointing_device (#10179)                                     

* Add hotfix for chibios keyboards not wake (#10088)                                               

* Add advanced/efficient RGB Matrix Indicators (#8564)                                             

* Naming change.                                                                                   

* Support for STM32 GPIOF,G,H,I,J,K (#10206)                                                       

* Add milc as a dependency and remove the installed milc (#10563)                                  

* ChibiOS upgrade: early init conversions (#10214)                                                 

* ChibiOS upgrade: configuration file migrator (#9952)                                             

* Haptic and solenoid cleanup (#9700)                                                              

* XD75 cleanup (#10524)                                                                            

* OLED display update interval support (#10388)                                                    

* Add definition based on currently-selected serial driver. (#10716)                               

* New feature: Retro Tapping per key (#10622)                                                      

* Allow for modification of output RGB values when using rgblight/rgb_matrix. (#10638)             

* Add housekeeping task callbacks so that keyboards/keymaps are capable of executing code for each main loop iteration. (#10530)

* Rescale both ChibiOS and AVR backlighting.                                                       

* Reduce Helix keyboard build variation (#8669)                                                    

* Minor change to behavior allowing display updates to continue between task ticks (#10750)        

* Some GPIO manipulations in matrix.c change to atomic. (#10491)                                   

* qmk cformat (#10767)                                                                             

* [Keyboard] Update the Speedo firmware for v3.0 (#10657)                                          

* Maartenwut/Maarten namechange to evyd13/Evy (#10274)                                             

* [quantum] combine repeated lines of code (#10837)                                                

* Add step sequencer feature (#9703)                                                               

* aeboards/ext65 refactor (#10820)                                                                 

* Refactor xelus/dawn60 for Rev2 later (#10584)                                                    

* add DEBUG_MATRIX_SCAN_RATE_ENABLE to common_features.mk (#10824)                                 

* [Core] Added `add_oneshot_mods` & `del_oneshot_mods` (#10549)                                    

* update chibios os usb for the otg driver (#8893)                                                 

* Remove HD44780 References, Part 4 (#10735)                                                       

* [Keyboard] Add Valor FRL TKL (+refactor) (#10512)                                                

* Fix cursor position bug in oled_write_raw functions (#10800)                                     

* Fixup version.h writing when using SKIP_VERSION=yes (#10972)                                     

* Allow for certain code in the codebase assuming length of string. (#10974)                       

* Add AT90USB support for serial.c (#10706)                                                        

* Auto shift: support repeats and early registration (#9826)                                       

* Rename ledmatrix.h to match .c file (#7949)                                                      

* Split RGB_MATRIX_ENABLE into _ENABLE and _DRIVER (#10231)                                        

* Split LED_MATRIX_ENABLE into _ENABLE and _DRIVER (#10840)                                        

* Merge point for 2020 Nov 28 Breaking Change                                                      

45 files changed, 1668 insertions, 122 deletions

diff --git a/quantum/backlight/backlight_avr.c b/quantum/backlight/backlight_avr.c
index b3e882ffe1..4d66da80ba 100644
--- a/quantum/backlight/backlight_avr.c
+++ b/quantum/backlight/backlight_avr.c
@@ -3,6 +3,11 @@
 #include "backlight_driver_common.h"
 #include "debug.h"
 
+// Maximum duty cycle limit
+#ifndef BACKLIGHT_LIMIT_VAL
+#    define BACKLIGHT_LIMIT_VAL 255
+#endif
+
 // This logic is a bit complex, we support 3 setups:
 //
 //   1. Hardware PWM when backlight is wired to a PWM pin.
@@ -240,6 +245,9 @@ static uint16_t cie_lightness(uint16_t v) {
     }
 }
 
+// rescale the supplied backlight value to be in terms of the value limit
+static uint32_t rescale_limit_val(uint32_t val) { return (val * (BACKLIGHT_LIMIT_VAL + 1)) / 256; }
+
 // range for val is [0..TIMER_TOP]. PWM pin is high while the timer count is below val.
 static inline void set_pwm(uint16_t val) { OCRxx = val; }
 
@@ -269,7 +277,7 @@ void backlight_set(uint8_t level) {
 #endif
     }
     // Set the brightness
-    set_pwm(cie_lightness(TIMER_TOP * (uint32_t)level / BACKLIGHT_LEVELS));
+    set_pwm(cie_lightness(rescale_limit_val(TIMER_TOP * (uint32_t)level / BACKLIGHT_LEVELS)));
 }
 
 void backlight_task(void) {}
@@ -375,7 +383,7 @@ ISR(TIMERx_OVF_vect)
         breathing_interrupt_disable();
     }
 
-    set_pwm(cie_lightness(scale_backlight((uint16_t)pgm_read_byte(&breathing_table[index]) * 0x0101U)));
+    set_pwm(cie_lightness(rescale_limit_val(scale_backlight((uint16_t)pgm_read_byte(&breathing_table[index]) * 0x0101U))));
 }
 
 #endif  // BACKLIGHT_BREATHING
diff --git a/quantum/backlight/backlight_chibios.c b/quantum/backlight/backlight_chibios.c
index 0fe812bf27..4d5a69e14e 100644
--- a/quantum/backlight/backlight_chibios.c
+++ b/quantum/backlight/backlight_chibios.c
@@ -3,6 +3,11 @@
 #include <hal.h>
 #include "debug.h"
 
+// Maximum duty cycle limit
+#ifndef BACKLIGHT_LIMIT_VAL
+#    define BACKLIGHT_LIMIT_VAL 255
+#endif
+
 // GPIOV2 && GPIOV3
 #ifndef BACKLIGHT_PAL_MODE
 #    define BACKLIGHT_PAL_MODE 2
@@ -58,6 +63,11 @@ static uint16_t cie_lightness(uint16_t v) {
     }
 }
 
+static uint32_t rescale_limit_val(uint32_t val) {
+    // rescale the supplied backlight value to be in terms of the value limit
+    return (val * (BACKLIGHT_LIMIT_VAL + 1)) / 256;
+}
+
 void backlight_init_ports(void) {
 #ifdef USE_GPIOV1
     palSetPadMode(PAL_PORT(BACKLIGHT_PIN), PAL_PAD(BACKLIGHT_PIN), PAL_MODE_STM32_ALTERNATE_PUSHPULL);
@@ -85,7 +95,7 @@ void backlight_set(uint8_t level) {
         pwmDisableChannel(&BACKLIGHT_PWM_DRIVER, BACKLIGHT_PWM_CHANNEL - 1);
     } else {
         // Turn backlight on
-        uint32_t duty = (uint32_t)(cie_lightness(0xFFFF * (uint32_t)level / BACKLIGHT_LEVELS));
+        uint32_t duty = (uint32_t)(cie_lightness(rescale_limit_val(0xFFFF * (uint32_t)level / BACKLIGHT_LEVELS)));
         pwmEnableChannel(&BACKLIGHT_PWM_DRIVER, BACKLIGHT_PWM_CHANNEL - 1, PWM_FRACTION_TO_WIDTH(&BACKLIGHT_PWM_DRIVER, 0xFFFF, duty));
     }
 }
@@ -129,7 +139,7 @@ void breathing_callback(PWMDriver *pwmp) {
     static uint16_t breathing_counter = 0;
     breathing_counter                 = (breathing_counter + 1) % (breathing_period * 256);
     uint8_t  index                    = breathing_counter / interval % BREATHING_STEPS;
-    uint32_t duty                     = cie_lightness(scale_backlight(breathing_table[index] * 256));
+    uint32_t duty                     = cie_lightness(rescale_limit_val(scale_backlight(breathing_table[index] * 256)));
 
     chSysLockFromISR();
     pwmEnableChannelI(pwmp, BACKLIGHT_PWM_CHANNEL - 1, PWM_FRACTION_TO_WIDTH(&BACKLIGHT_PWM_DRIVER, 0xFFFF, duty));
diff --git a/quantum/config_common.h b/quantum/config_common.h
index c1e6698e50..2d9c70b08d 100644
--- a/quantum/config_common.h
+++ b/quantum/config_common.h
@@ -39,7 +39,7 @@
 #        define PIND_ADDRESS 0x9
 #        define PINE_ADDRESS 0xC
 #        define PINF_ADDRESS 0xF
-#    elif defined(__AVR_ATmega32U2__) || defined(__AVR_ATmega16U2__)
+#    elif defined(__AVR_ATmega32U2__) || defined(__AVR_ATmega16U2__) || defined(__AVR_ATmega328P__) || defined(__AVR_ATmega328__)
 #        define ADDRESS_BASE 0x00
 #        define PINB_ADDRESS 0x3
 #        define PINC_ADDRESS 0x6
@@ -58,11 +58,6 @@
 #        define PINC_ADDRESS 0x3
 #        define PINB_ADDRESS 0x6
 #        define PINA_ADDRESS 0x9
-#    elif defined(__AVR_ATmega328P__) || defined(__AVR_ATmega328__)
-#        define ADDRESS_BASE 0x00
-#        define PINB_ADDRESS 0x3
-#        define PINC_ADDRESS 0x6
-#        define PIND_ADDRESS 0x9
 #    elif defined(__AVR_ATtiny85__)
 #        define ADDRESS_BASE 0x10
 #        define PINB_ADDRESS 0x6
@@ -284,6 +279,91 @@
 #        define F13 PAL_LINE(GPIOF, 13)
 #        define F14 PAL_LINE(GPIOF, 14)
 #        define F15 PAL_LINE(GPIOF, 15)
+#        define G0 PAL_LINE(GPIOG, 0)
+#        define G1 PAL_LINE(GPIOG, 1)
+#        define G2 PAL_LINE(GPIOG, 2)
+#        define G3 PAL_LINE(GPIOG, 3)
+#        define G4 PAL_LINE(GPIOG, 4)
+#        define G5 PAL_LINE(GPIOG, 5)
+#        define G6 PAL_LINE(GPIOG, 6)
+#        define G7 PAL_LINE(GPIOG, 7)
+#        define G8 PAL_LINE(GPIOG, 8)
+#        define G9 PAL_LINE(GPIOG, 9)
+#        define G10 PAL_LINE(GPIOG, 10)
+#        define G11 PAL_LINE(GPIOG, 11)
+#        define G12 PAL_LINE(GPIOG, 12)
+#        define G13 PAL_LINE(GPIOG, 13)
+#        define G14 PAL_LINE(GPIOG, 14)
+#        define G15 PAL_LINE(GPIOG, 15)
+#        define H0 PAL_LINE(GPIOH, 0)
+#        define H1 PAL_LINE(GPIOH, 1)
+#        define H2 PAL_LINE(GPIOH, 2)
+#        define H3 PAL_LINE(GPIOH, 3)
+#        define H4 PAL_LINE(GPIOH, 4)
+#        define H5 PAL_LINE(GPIOH, 5)
+#        define H6 PAL_LINE(GPIOH, 6)
+#        define H7 PAL_LINE(GPIOH, 7)
+#        define H8 PAL_LINE(GPIOH, 8)
+#        define H9 PAL_LINE(GPIOH, 9)
+#        define H10 PAL_LINE(GPIOH, 10)
+#        define H11 PAL_LINE(GPIOH, 11)
+#        define H12 PAL_LINE(GPIOH, 12)
+#        define H13 PAL_LINE(GPIOH, 13)
+#        define H14 PAL_LINE(GPIOH, 14)
+#        define H15 PAL_LINE(GPIOH, 15)
+#        define I0 PAL_LINE(GPIOI, 0)
+#        define I1 PAL_LINE(GPIOI, 1)
+#        define I2 PAL_LINE(GPIOI, 2)
+#        define I3 PAL_LINE(GPIOI, 3)
+#        define I4 PAL_LINE(GPIOI, 4)
+#        define I5 PAL_LINE(GPIOI, 5)
+#        define I6 PAL_LINE(GPIOI, 6)
+#        define I7 PAL_LINE(GPIOI, 7)
+#        define I8 PAL_LINE(GPIOI, 8)
+#        define I9 PAL_LINE(GPIOI, 9)
+#        define I10 PAL_LINE(GPIOI, 10)
+#        define I11 PAL_LINE(GPIOI, 11)
+#        define I12 PAL_LINE(GPIOI, 12)
+#        define I13 PAL_LINE(GPIOI, 13)
+#        define I14 PAL_LINE(GPIOI, 14)
+#        define I15 PAL_LINE(GPIOI, 15)
+#        define J0 PAL_LINE(GPIOJ, 0)
+#        define J1 PAL_LINE(GPIOJ, 1)
+#        define J2 PAL_LINE(GPIOJ, 2)
+#        define J3 PAL_LINE(GPIOJ, 3)
+#        define J4 PAL_LINE(GPIOJ, 4)
+#        define J5 PAL_LINE(GPIOJ, 5)
+#        define J6 PAL_LINE(GPIOJ, 6)
+#        define J7 PAL_LINE(GPIOJ, 7)
+#        define J8 PAL_LINE(GPIOJ, 8)
+#        define J9 PAL_LINE(GPIOJ, 9)
+#        define J10 PAL_LINE(GPIOJ, 10)
+#        define J11 PAL_LINE(GPIOJ, 11)
+#        define J12 PAL_LINE(GPIOJ, 12)
+#        define J13 PAL_LINE(GPIOJ, 13)
+#        define J14 PAL_LINE(GPIOJ, 14)
+#        define J15 PAL_LINE(GPIOJ, 15)
+// Keyboards can `#define KEYBOARD_REQUIRES_GPIOK` if they need to access GPIO-K pins. These conflict with a whole
+// bunch of layout definitions, so it's intentionally left out unless absolutely required -- in that case, the
+// keyboard designer should use a different symbol when defining their layout macros.
+#        ifdef KEYBOARD_REQUIRES_GPIOK
+#            define K0 PAL_LINE(GPIOK, 0)
+#            define K1 PAL_LINE(GPIOK, 1)
+#            define K2 PAL_LINE(GPIOK, 2)
+#            define K3 PAL_LINE(GPIOK, 3)
+#            define K4 PAL_LINE(GPIOK, 4)
+#            define K5 PAL_LINE(GPIOK, 5)
+#            define K6 PAL_LINE(GPIOK, 6)
+#            define K7 PAL_LINE(GPIOK, 7)
+#            define K8 PAL_LINE(GPIOK, 8)
+#            define K9 PAL_LINE(GPIOK, 9)
+#            define K10 PAL_LINE(GPIOK, 10)
+#            define K11 PAL_LINE(GPIOK, 11)
+#            define K12 PAL_LINE(GPIOK, 12)
+#            define K13 PAL_LINE(GPIOK, 13)
+#            define K14 PAL_LINE(GPIOK, 14)
+#            define K15 PAL_LINE(GPIOK, 15)
+#        endif
 #    endif
 #endif
 
diff --git a/quantum/encoder.c b/quantum/encoder.c
index 81ec1bb376..7ca31afedc 100644
--- a/quantum/encoder.c
+++ b/quantum/encoder.c
@@ -23,7 +23,7 @@
 // for memcpy
 #include <string.h>
 
-#ifndef ENCODER_RESOLUTION
+#if !defined(ENCODER_RESOLUTIONS) && !defined(ENCODER_RESOLUTION)
 #    define ENCODER_RESOLUTION 4
 #endif
 
@@ -34,6 +34,9 @@
 #define NUMBER_OF_ENCODERS (sizeof(encoders_pad_a) / sizeof(pin_t))
 static pin_t encoders_pad_a[] = ENCODERS_PAD_A;
 static pin_t encoders_pad_b[] = ENCODERS_PAD_B;
+#ifdef ENCODER_RESOLUTIONS
+static uint8_t encoder_resolutions[] = ENCODER_RESOLUTIONS;
+#endif
 
 #ifndef ENCODER_DIRECTION_FLIP
 #    define ENCODER_CLOCKWISE true
@@ -65,9 +68,15 @@ void encoder_init(void) {
     if (!isLeftHand) {
         const pin_t encoders_pad_a_right[] = ENCODERS_PAD_A_RIGHT;
         const pin_t encoders_pad_b_right[] = ENCODERS_PAD_B_RIGHT;
+#    if defined(ENCODER_RESOLUTIONS_RIGHT)
+        const uint8_t encoder_resolutions_right[] = ENCODER_RESOLUTIONS_RIGHT;
+#    endif
         for (uint8_t i = 0; i < NUMBER_OF_ENCODERS; i++) {
             encoders_pad_a[i] = encoders_pad_a_right[i];
             encoders_pad_b[i] = encoders_pad_b_right[i];
+#    if defined(ENCODER_RESOLUTIONS_RIGHT)
+            encoder_resolutions[i] = encoder_resolutions_right[i];
+#    endif
         }
     }
 #endif
@@ -87,19 +96,26 @@ void encoder_init(void) {
 
 static void encoder_update(int8_t index, uint8_t state) {
     uint8_t i = index;
+
+#ifdef ENCODER_RESOLUTIONS
+    int8_t resolution = encoder_resolutions[i];
+#else
+    int8_t resolution = ENCODER_RESOLUTION;
+#endif
+
 #ifdef SPLIT_KEYBOARD
     index += thisHand;
 #endif
     encoder_pulses[i] += encoder_LUT[state & 0xF];
-    if (encoder_pulses[i] >= ENCODER_RESOLUTION) {
+    if (encoder_pulses[i] >= resolution) {
         encoder_value[index]++;
         encoder_update_kb(index, ENCODER_COUNTER_CLOCKWISE);
     }
-    if (encoder_pulses[i] <= -ENCODER_RESOLUTION) {  // direction is arbitrary here, but this clockwise
+    if (encoder_pulses[i] <= -resolution) {  // direction is arbitrary here, but this clockwise
         encoder_value[index]--;
         encoder_update_kb(index, ENCODER_CLOCKWISE);
     }
-    encoder_pulses[i] %= ENCODER_RESOLUTION;
+    encoder_pulses[i] %= resolution;
 }
 
 void encoder_read(void) {
diff --git a/quantum/joystick.h b/quantum/joystick.h
index a95472b9fd..87dbc24aff 100644
--- a/quantum/joystick.h
+++ b/quantum/joystick.h
@@ -1,5 +1,9 @@
 #pragma once
 
+#include "quantum.h"
+
+#include <stdint.h>
+
 #ifndef JOYSTICK_BUTTON_COUNT
 #    define JOYSTICK_BUTTON_COUNT 8
 #endif
@@ -8,9 +12,13 @@
 #    define JOYSTICK_AXES_COUNT 4
 #endif
 
-#include "quantum.h"
+#ifndef JOYSTICK_AXES_RESOLUTION
+#    define JOYSTICK_AXES_RESOLUTION 8
+#elif JOYSTICK_AXES_RESOLUTION < 8 || JOYSTICK_AXES_RESOLUTION > 16
+#    error JOYSTICK_AXES_RESOLUTION must be between 8 and 16
+#endif
 
-#include <stdint.h>
+#define JOYSTICK_RESOLUTION ((1L << (JOYSTICK_AXES_RESOLUTION - 1)) - 1)
 
 // configure on input_pin of the joystick_axes array entry to JS_VIRTUAL_AXIS
 // to prevent it from being read from the ADC. This allows outputing forged axis value.
diff --git a/quantum/led_matrix.c b/quantum/led_matrix.c
index 5c24c797a9..eb523990a6 100644
--- a/quantum/led_matrix.c
+++ b/quantum/led_matrix.c
@@ -20,7 +20,7 @@
 #include <stdint.h>
 #include <stdbool.h>
 #include "quantum.h"
-#include "ledmatrix.h"
+#include "led_matrix.h"
 #include "progmem.h"
 #include "config.h"
 #include "eeprom.h"
diff --git a/quantum/ledmatrix.h b/quantum/led_matrix.h
index 5867ba9876..5867ba9876 100644
--- a/quantum/ledmatrix.h
+++ b/quantum/led_matrix.h
diff --git a/quantum/led_matrix_drivers.c b/quantum/led_matrix_drivers.c
index 6877bf4c6b..9decaa33c2 100644
--- a/quantum/led_matrix_drivers.c
+++ b/quantum/led_matrix_drivers.c
@@ -18,7 +18,7 @@
 #include <stdint.h>
 #include <stdbool.h>
 #include "quantum.h"
-#include "ledmatrix.h"
+#include "led_matrix.h"
 
 /* Each driver needs to define a struct:
  *
diff --git a/quantum/matrix.c b/quantum/matrix.c
index c68c56cac2..cab0d2ddca 100644
--- a/quantum/matrix.c
+++ b/quantum/matrix.c
@@ -32,6 +32,19 @@ static const pin_t col_pins[MATRIX_COLS] = MATRIX_COL_PINS;
 extern matrix_row_t raw_matrix[MATRIX_ROWS];  // raw values
 extern matrix_row_t matrix[MATRIX_ROWS];      // debounced values
 
+static inline void setPinOutput_writeLow(pin_t pin) {
+    ATOMIC_BLOCK_FORCEON {
+        setPinOutput(pin);
+        writePinLow(pin);
+    }
+}
+
+static inline void setPinInputHigh_atomic(pin_t pin) {
+    ATOMIC_BLOCK_FORCEON {
+        setPinInputHigh(pin);
+    }
+}
+
 // matrix code
 
 #ifdef DIRECT_PINS
@@ -70,22 +83,23 @@ static bool read_cols_on_row(matrix_row_t current_matrix[], uint8_t current_row)
 #    if (DIODE_DIRECTION == COL2ROW)
 
 static void select_row(uint8_t row) {
-    setPinOutput(row_pins[row]);
-    writePinLow(row_pins[row]);
+    setPinOutput_writeLow(row_pins[row]);
 }
 
-static void unselect_row(uint8_t row) { setPinInputHigh(row_pins[row]); }
+static void unselect_row(uint8_t row) {
+    setPinInputHigh_atomic(row_pins[row]);
+}
 
 static void unselect_rows(void) {
     for (uint8_t x = 0; x < MATRIX_ROWS; x++) {
-        setPinInputHigh(row_pins[x]);
+        setPinInputHigh_atomic(row_pins[x]);
     }
 }
 
 static void init_pins(void) {
     unselect_rows();
     for (uint8_t x = 0; x < MATRIX_COLS; x++) {
-        setPinInputHigh(col_pins[x]);
+        setPinInputHigh_atomic(col_pins[x]);
     }
 }
 
@@ -120,22 +134,23 @@ static bool read_cols_on_row(matrix_row_t current_matrix[], uint8_t current_row)
 #    elif (DIODE_DIRECTION == ROW2COL)
 
 static void select_col(uint8_t col) {
-    setPinOutput(col_pins[col]);
-    writePinLow(col_pins[col]);
+    setPinOutput_writeLow(col_pins[col]);
 }
 
-static void unselect_col(uint8_t col) { setPinInputHigh(col_pins[col]); }
+static void unselect_col(uint8_t col) {
+    setPinInputHigh_atomic(col_pins[col]);
+}
 
 static void unselect_cols(void) {
     for (uint8_t x = 0; x < MATRIX_COLS; x++) {
-        setPinInputHigh(col_pins[x]);
+        setPinInputHigh_atomic(col_pins[x]);
     }
 }
 
 static void init_pins(void) {
     unselect_cols();
     for (uint8_t x = 0; x < MATRIX_ROWS; x++) {
-        setPinInputHigh(row_pins[x]);
+        setPinInputHigh_atomic(row_pins[x]);
     }
 }
 
diff --git a/quantum/mcu_selection.mk b/quantum/mcu_selection.mk
index 295dfd3189..9518a6463f 100644
--- a/quantum/mcu_selection.mk
+++ b/quantum/mcu_selection.mk
@@ -318,6 +318,9 @@ ifneq (,$(filter $(MCU),atmega16u2 atmega32u2 atmega16u4 atmega32u4 at90usb646 a
   ifeq (,$(filter $(NO_INTERRUPT_CONTROL_ENDPOINT),yes))
     OPT_DEFS += -DINTERRUPT_CONTROL_ENDPOINT
   endif
+  ifneq (,$(filter $(MCU),atmega16u2 atmega32u2))
+    NO_I2C = yes
+  endif
 endif
 
 ifneq (,$(filter $(MCU),atmega32a))
diff --git a/quantum/process_keycode/process_auto_shift.c b/quantum/process_keycode/process_auto_shift.c
index b1267922ce..a2d315408b 100644
--- a/quantum/process_keycode/process_auto_shift.c
+++ b/quantum/process_keycode/process_auto_shift.c
@@ -16,48 +16,149 @@
 
 #ifdef AUTO_SHIFT_ENABLE
 
+#    include <stdbool.h>
 #    include <stdio.h>
 
 #    include "process_auto_shift.h"
 
-static bool     autoshift_enabled = true;
 static uint16_t autoshift_time    = 0;
 static uint16_t autoshift_timeout = AUTO_SHIFT_TIMEOUT;
 static uint16_t autoshift_lastkey = KC_NO;
+static struct {
+    // Whether autoshift is enabled.
+    bool enabled : 1;
+    // Whether the last auto-shifted key was released after the timeout.  This
+    // is used to replicate the last key for a tap-then-hold.
+    bool lastshifted : 1;
+    // Whether an auto-shiftable key has been pressed but not processed.
+    bool in_progress : 1;
+    // Whether the auto-shifted keypress has been registered.
+    bool holding_shift : 1;
+} autoshift_flags = {true, false, false, false};
+
+/** \brief Record the press of an autoshiftable key
+ *
+ *  \return Whether the record should be further processed.
+ */
+static bool autoshift_press(uint16_t keycode, uint16_t now, keyrecord_t *record) {
+    if (!autoshift_flags.enabled) {
+        return true;
+    }
+
+#    ifndef AUTO_SHIFT_MODIFIERS
+    if (get_mods() & (~MOD_BIT(KC_LSFT))) {
+        return true;
+    }
+#    endif
+#    ifdef AUTO_SHIFT_REPEAT
+    const uint16_t elapsed = TIMER_DIFF_16(now, autoshift_time);
+#        ifndef AUTO_SHIFT_NO_AUTO_REPEAT
+    if (!autoshift_flags.lastshifted) {
+#        endif
+        if (elapsed < TAPPING_TERM && keycode == autoshift_lastkey) {
+            // Allow a tap-then-hold for keyrepeat.
+            if (!autoshift_flags.lastshifted) {
+                register_code(autoshift_lastkey);
+            } else {
+                // Simulate pressing the shift key.
+                add_weak_mods(MOD_BIT(KC_LSFT));
+                register_code(autoshift_lastkey);
+            }
+            return false;
+        }
+#        ifndef AUTO_SHIFT_NO_AUTO_REPEAT
+    }
+#        endif
+#    endif
 
-void autoshift_flush(void) {
-    if (autoshift_lastkey != KC_NO) {
-        uint16_t elapsed = timer_elapsed(autoshift_time);
+    // Record the keycode so we can simulate it later.
+    autoshift_lastkey           = keycode;
+    autoshift_time              = now;
+    autoshift_flags.in_progress = true;
 
-        if (elapsed > autoshift_timeout) {
-            tap_code16(LSFT(autoshift_lastkey));
+#    if !defined(NO_ACTION_ONESHOT) && !defined(NO_ACTION_TAPPING)
+    clear_oneshot_layer_state(ONESHOT_OTHER_KEY_PRESSED);
+#    endif
+    return false;
+}
+
+/** \brief Registers an autoshiftable key under the right conditions
+ *
+ * If the autoshift delay has elapsed, register a shift and the key.
+ *
+ * If the autoshift key is released before the delay has elapsed, register the
+ * key without a shift.
+ */
+static void autoshift_end(uint16_t keycode, uint16_t now, bool matrix_trigger) {
+    // Called on key down with KC_NO, auto-shifted key up, and timeout.
+    if (autoshift_flags.in_progress) {
+        // Process the auto-shiftable key.
+        autoshift_flags.in_progress = false;
+
+        // Time since the initial press was recorded.
+        const uint16_t elapsed = TIMER_DIFF_16(now, autoshift_time);
+        if (elapsed < autoshift_timeout) {
+            register_code(autoshift_lastkey);
+            autoshift_flags.lastshifted = false;
         } else {
-            tap_code(autoshift_lastkey);
+            // Simulate pressing the shift key.
+            add_weak_mods(MOD_BIT(KC_LSFT));
+            register_code(autoshift_lastkey);
+            autoshift_flags.lastshifted = true;
+#    if defined(AUTO_SHIFT_REPEAT) && !defined(AUTO_SHIFT_NO_AUTO_REPEAT)
+            if (matrix_trigger) {
+                // Prevents release.
+                return;
+            }
+#    endif
         }
 
-        autoshift_time    = 0;
-        autoshift_lastkey = KC_NO;
+#    if TAP_CODE_DELAY > 0
+        wait_ms(TAP_CODE_DELAY);
+#    endif
+        unregister_code(autoshift_lastkey);
+        del_weak_mods(MOD_BIT(KC_LSFT));
+    } else {
+        // Release after keyrepeat.
+        unregister_code(keycode);
+        if (keycode == autoshift_lastkey) {
+            // This will only fire when the key was the last auto-shiftable
+            // pressed. That prevents aaaaBBBB then releasing a from unshifting
+            // later Bs (if B wasn't auto-shiftable).
+            del_weak_mods(MOD_BIT(KC_LSFT));
+        }
     }