ARM - Initial backlight support (#6487)0.7.31

* Move AVR backlight to own file, add borrowed ARM implementation

* Tiny fix for backlight custom logic

* Remove duplicate board from rebase

* Fix f303 onekey example

* clang-format

* clang-format

* Remove backlight keymap debug

* Initial pass of ARM backlight docs

* Initial pass of ARM backlight docs - resolve todos

* fix rules validation logic

* Add f072 warning

* Add f072 warning

* tidy up breathing in backlight keymap

* tidy up breathing in backlight keymap

* add missing break to backlight keymap

17 files changed, 860 insertions, 529 deletions

diff --git a/common_features.mk b/common_features.mk
index 79af8a2256..05a99fc63c 100644
--- a/common_features.mk
+++ b/common_features.mk
@@ -229,13 +229,32 @@ ifeq ($(strip $(LCD_ENABLE)), yes)
     CIE1931_CURVE = yes
 endif
 
-ifeq ($(strip $(BACKLIGHT_ENABLE)), yes)
+# backward compat
+ifeq ($(strip $(BACKLIGHT_CUSTOM_DRIVER)), yes)
+    BACKLIGHT_ENABLE = custom
+endif
+
+VALID_BACKLIGHT_TYPES := yes custom
+
+BACKLIGHT_ENABLE ?= no
+ifneq ($(strip $(BACKLIGHT_ENABLE)), no)
+    ifeq ($(filter $(BACKLIGHT_ENABLE),$(VALID_BACKLIGHT_TYPES)),)
+        $(error BACKLIGHT_ENABLE="$(BACKLIGHT_ENABLE)" is not a valid backlight type)
+    endif
+
     ifeq ($(strip $(VISUALIZER_ENABLE)), yes)
         CIE1931_CURVE = yes
     endif
-    ifeq ($(strip $(BACKLIGHT_CUSTOM_DRIVER)), yes)
+
+    ifeq ($(strip $(BACKLIGHT_ENABLE)), custom)
         OPT_DEFS += -DBACKLIGHT_CUSTOM_DRIVER
     endif
+
+    ifeq ($(PLATFORM),AVR)
+        SRC += $(QUANTUM_DIR)/backlight/backlight_avr.c
+    else
+        SRC += $(QUANTUM_DIR)/backlight/backlight_arm.c
+    endif
 endif
 
 ifeq ($(strip $(CIE1931_CURVE)), yes)
diff --git a/docs/feature_backlight.md b/docs/feature_backlight.md
index 556da73859..6a2946fd6d 100644
--- a/docs/feature_backlight.md
+++ b/docs/feature_backlight.md
@@ -1,6 +1,8 @@
 # Backlighting
 
-Many keyboards support backlit keys by way of individual LEDs placed through or underneath the keyswitches. QMK is able to control the brightness of these LEDs by switching them on and off rapidly in a certain ratio, a technique known as *Pulse Width Modulation*, or PWM. By altering the duty cycle of the PWM signal, it creates the illusion of dimming.
+Many keyboards support backlit keys by way of individual LEDs placed through or underneath the keyswitches. This feature is distinct from both the [RGB underglow](feature_rgblight.md) and [RGB matrix](feature_rgb_matrix.md) features as it usually allows for only a single colour per switch, though you can obviously install multiple different single coloured LEDs on a keyboard.
+
+QMK is able to control the brightness of these LEDs by switching them on and off rapidly in a certain ratio, a technique known as *Pulse Width Modulation*, or PWM. By altering the duty cycle of the PWM signal, it creates the illusion of dimming.
 
 The MCU can only supply so much current to its GPIO pins. Instead of powering the backlight directly from the MCU, the backlight pin is connected to a transistor or MOSFET that switches the power to the LEDs.
 
@@ -12,9 +14,8 @@ Most keyboards have backlighting enabled by default if they support it, but if i
 BACKLIGHT_ENABLE = yes
 ```
 
-You should then be able to use the keycodes below to change the backlight level.
-
 ## Keycodes
+Once enabled the following keycodes below can be used to change the backlight level.
 
 |Key      |Description                               |
 |---------|------------------------------------------|
@@ -26,9 +27,9 @@ You should then be able to use the keycodes below to change the backlight level.
 |`BL_DEC` |Decrease the backlight level              |
 |`BL_BRTG`|Toggle backlight breathing                |
 
-## Caveats
+## AVR driver
 
-This feature is distinct from both the [RGB underglow](feature_rgblight.md) and [RGB matrix](feature_rgb_matrix.md) features as it usually allows for only a single colour per switch, though you can obviously use multiple different coloured LEDs on a keyboard.
+### Caveats
 
 Hardware PWM is supported according to the following table:
 
@@ -58,9 +59,9 @@ All other pins will use software PWM. If the [Audio](feature_audio.md) feature i
 
 When both timers are in use for Audio, the backlight PWM will not use a hardware timer, but will instead be triggered during the matrix scan. In this case, breathing is not supported, and the backlight might flicker, because the PWM computation may not be called with enough timing precision.
 
-## Configuration
+### AVR Configuration
 
-To change the behaviour of the backlighting, `#define` these in your `config.h`:
+To change the behavior of the backlighting, `#define` these in your `config.h`:
 
 |Define               |Default      |Description                                                                                                  |
 |---------------------|-------------|-------------------------------------------------------------------------------------------------------------|
@@ -72,14 +73,14 @@ To change the behaviour of the backlighting, `#define` these in your `config.h`:
 |`BREATHING_PERIOD`   |`6`          |The length of one backlight "breath" in seconds                                                              |
 |`BACKLIGHT_ON_STATE` |`0`          |The state of the backlight pin when the backlight is "on" - `1` for high, `0` for low                        |
 
-## Backlight On State
+### Backlight On State
 
 Most backlight circuits are driven by an N-channel MOSFET or NPN transistor. This means that to turn the transistor *on* and light the LEDs, you must drive the backlight pin, connected to the gate or base, *high*.
 Sometimes, however, a P-channel MOSFET, or a PNP transistor is used. In this case, when the transistor is on, the pin is driven *low* instead.
 
 This functionality is configured at the keyboard level with the `BACKLIGHT_ON_STATE` define.
 
-## Multiple backlight pins
+### Multiple backlight pins
 
 Most keyboards have only one backlight pin which control all backlight LEDs (especially if the backlight is connected to an hardware PWM pin).
 In software PWM, it is possible to define multiple backlight pins. All those pins will be turned on and off at the same time during the PWM duty cycle.
@@ -87,13 +88,13 @@ This feature allows to set for instance the Caps Lock LED (or any other controll
 
 To activate multiple backlight pins, you need to add something like this to your user `config.h`:
 
-~~~c
+```c
 #define BACKLIGHT_LED_COUNT 2
 #undef BACKLIGHT_PIN
 #define BACKLIGHT_PINS { F5, B2 }
-~~~
+```
 
-## Hardware PWM Implementation
+### Hardware PWM Implementation
 
 When using the supported pins for backlighting, QMK will use a hardware timer configured to output a PWM signal. This timer will count up to `ICRx` (by default `0xFFFF`) before resetting to 0.
 The desired brightness is calculated and stored in the `OCRxx` register. When the counter reaches this value, the backlight pin will go low, and is pulled high again when the counter resets.
@@ -102,7 +103,7 @@ In this way `OCRxx` essentially controls the duty cycle of the LEDs, and thus th
 The breathing effect is achieved by registering an interrupt handler for `TIMER1_OVF_vect` that is called whenever the counter resets, roughly 244 times per second.
 In this handler, the value of an incrementing counter is mapped onto a precomputed brightness curve. To turn off breathing, the interrupt handler is simply disabled, and the brightness reset to the level stored in EEPROM.
 
-## Software PWM Implementation
+### Software PWM Implementation
 
 When `BACKLIGHT_PIN` is not set to a hardware backlight pin, QMK will use a hardware timer configured to trigger software interrupts. This time will count up to `ICRx` (by default `0xFFFF`) before resetting to 0.
 When resetting to 0, the CPU will fire an OVF (overflow) interrupt that will turn the LEDs on, starting the duty cycle.
@@ -111,6 +112,29 @@ In this way `OCRxx` essentially controls the duty cycle of the LEDs, and thus th
 
 The breathing effect is the same as in the hardware PWM implementation.
 
+## ARM Driver
+
+### Caveats
+
+Currently only hardware PWM is supported, and does not provide automatic configuration.
+
+?> STMF072 support is being investigated.
+
+### ARM Configuration
+
+To change the behavior of the backlighting, `#define` these in your `config.h`:
+
+|Define                  |Default      |Description                                                                                                  |
+|------------------------|-------------|-------------------------------------------------------------------------------------------------------------|
+|`BACKLIGHT_PIN`         |`B7`         |The pin that controls the LEDs. Unless you are designing your own keyboard, you shouldn't need to change this|
+|`BACKLIGHT_PWM_DRIVER`  |`PWMD4`      |The PWM driver to use, see ST datasheets for pin to PWM timer mapping. Unless you are designing your own keyboard, you shouldn't need to change this|
+|`BACKLIGHT_PWM_CHANNEL` |`3`          |The PWM channel to use, see ST datasheets for pin to PWM channel mapping. Unless you are designing your own keyboard, you shouldn't need to change this|
+|`BACKLIGHT_PAL_MODE`    |`2`          |The pin alternative function to use, see ST datasheets for pin AF mapping. Unless you are designing your own keyboard, you shouldn't need to change this|
+|`BACKLIGHT_LEVELS`      |`3`          |The number of brightness levels (maximum 31 excluding off)                                                   |
+|`BACKLIGHT_CAPS_LOCK`   |*Not defined*|Enable Caps Lock indicator using backlight (for keyboards without dedicated LED)                             |
+|`BACKLIGHT_BREATHING`   |*Not defined*|Enable backlight breathing, if supported                                                                     |
+|`BREATHING_PERIOD`      |`6`          |The length of one backlight "breath" in seconds                                                              |
+
 ## Backlight Functions
 
 |Function  |Description                                                |
diff --git a/keyboards/handwired/onekey/bluepill/config.h b/keyboards/handwired/onekey/bluepill/config.h
index 3d88ee00e5..81282ae1ff 100644
--- a/keyboards/handwired/onekey/bluepill/config.h
+++ b/keyboards/handwired/onekey/bluepill/config.h
@@ -21,3 +21,7 @@
 #define MATRIX_COL_PINS { B0 }
 #define MATRIX_ROW_PINS { A7 }
 #define UNUSED_PINS
+
+#define BACKLIGHT_PIN           A0
+#define BACKLIGHT_PWM_DRIVER    PWMD2
+#define BACKLIGHT_PWM_CHANNEL   1
diff --git a/keyboards/handwired/onekey/bluepill/halconf.h b/keyboards/handwired/onekey/bluepill/halconf.h
index 72879a575b..53b2f91e33 100644
--- a/keyboards/handwired/onekey/bluepill/halconf.h
+++ b/keyboards/handwired/onekey/bluepill/halconf.h
@@ -146,7 +146,7 @@
  * @brief   Enables the SPI subsystem.
  */
 #if !defined(HAL_USE_SPI) || defined(__DOXYGEN__)
-#define HAL_USE_SPI                 TRUE
+#define HAL_USE_SPI                 FALSE
 #endif
 
 /**
diff --git a/keyboards/handwired/onekey/bluepill/mcuconf.h b/keyboards/handwired/onekey/bluepill/mcuconf.h
index fced27289e..a645d3c5d5 100644
--- a/keyboards/handwired/onekey/bluepill/mcuconf.h
+++ b/keyboards/handwired/onekey/bluepill/mcuconf.h
@@ -132,8 +132,8 @@
  * PWM driver system settings.
  */
 #define STM32_PWM_USE_ADVANCED              FALSE
-#define STM32_PWM_USE_TIM1                  TRUE
-#define STM32_PWM_USE_TIM2                  FALSE
+#define STM32_PWM_USE_TIM1                  FALSE
+#define STM32_PWM_USE_TIM2                  TRUE
 #define STM32_PWM_USE_TIM3                  FALSE
 #define STM32_PWM_USE_TIM4                  FALSE
 #define STM32_PWM_USE_TIM5                  FALSE
@@ -168,7 +168,7 @@
  * SPI driver system settings.
  */
 #define STM32_SPI_USE_SPI1                  FALSE
-#define STM32_SPI_USE_SPI2                  TRUE
+#define STM32_SPI_USE_SPI2                  FALSE
 #define STM32_SPI_USE_SPI3                  FALSE
 #define STM32_SPI_SPI1_DMA_PRIORITY         1
 #define STM32_SPI_SPI2_DMA_PRIORITY         1
diff --git a/keyboards/handwired/onekey/bluepill/rules.mk b/keyboards/handwired/onekey/bluepill/rules.mk
index 46274066dd..aeda2782b9 100644
--- a/keyboards/handwired/onekey/bluepill/rules.mk
+++ b/keyboards/handwired/onekey/bluepill/rules.mk
@@ -1,7 +1,11 @@
 # GENERIC STM32F103C8T6 board - stm32duino bootloader
+BOARD = GENERIC_STM32_F103
+
 OPT_DEFS = -DCORTEX_VTOR_INIT=0x2000
 MCU_LDSCRIPT = STM32F103x8_stm32duino_bootloader
-BOARD = GENERIC_STM32_F103
+
+DFU_ARGS = -d 1eaf:0003 -a2 -R
+DFU_SUFFIX_ARGS ?= -v 1eaf -p 0003
 
 # OPT_DEFS =
 # MCU_LDSCRIPT = STM32F103x8
diff --git a/keyboards/handwired/onekey/config.h b/keyboards/handwired/onekey/config.h
index 6f7ec1289f..64a447481d 100644
--- a/keyboards/handwired/onekey/config.h
+++ b/keyboards/handwired/onekey/config.h
@@ -35,6 +35,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 /* Set 0 if debouncing isn't needed */
 #define DEBOUNCE    5
 
+#define TAPPING_TERM 500
+
 /* Mechanical locking support. Use KC_LCAP, KC_LNUM or KC_LSCR instead in keymap */
 #define LOCKING_SUPPORT_ENABLE
 /* Locking resynchronize hack */
diff --git a/keyboards/handwired/onekey/keymaps/backlight/config.h b/keyboards/handwired/onekey/keymaps/backlight/config.h
new file mode 100644
index 0000000000..af01528b43
--- /dev/null
+++ b/keyboards/handwired/onekey/keymaps/backlight/config.h
@@ -0,0 +1,3 @@
+#pragma once
+
+#define BACKLIGHT_BREATHING
diff --git a/keyboards/handwired/onekey/keymaps/backlight/keymap.c b/keyboards/handwired/onekey/keymaps/backlight/keymap.c
new file mode 100644
index 0000000000..1f4be16a62
--- /dev/null
+++ b/keyboards/handwired/onekey/keymaps/backlight/keymap.c
@@ -0,0 +1,40 @@
+#include QMK_KEYBOARD_H
+
+//Tap Dance Declarations
+enum {
+  TD_BL = 0
+};
+
+void dance_cln_finished (qk_tap_dance_state_t *state, void *user_data) {
+  // noop
+}
+
+void dance_cln_reset (qk_tap_dance_state_t *state, void *user_data) {
+  switch (state->count) {
+    case 1:
+      // single tap - step through backlight
+      backlight_step();
+      break;
+#ifdef BACKLIGHT_BREATHING
+    case 2:
+      // double tap - toggle breathing
+      breathing_toggle();
+      break;
+    case 3:
+      //tripple tap - do some pulse stuff
+      breathing_pulse();
+      break;
+#endif
+    default:
+      // more - nothing
+      break;
+  }
+}
+
+qk_tap_dance_action_t tap_dance_actions[] = {
+  [TD_BL]  = ACTION_TAP_DANCE_FN_ADVANCED (NULL, dance_cln_finished, dance_cln_reset)
+};
+
+const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
+  LAYOUT( TD(TD_BL) )
+};
diff --git a/keyboards/handwired/onekey/keymaps/backlight/rules.mk b/keyboards/handwired/onekey/keymaps/backlight/rules.mk
new file mode 100644
index 0000000000..176e099770
--- /dev/null
+++ b/keyboards/handwired/onekey/keymaps/backlight/rules.mk
@@ -0,0 +1,2 @@
+BACKLIGHT_ENABLE = yes
+TAP_DANCE_ENABLE = yes
diff --git a/keyboards/handwired/onekey/proton_c/config.h b/keyboards/handwired/onekey/proton_c/config.h
index f6bedcfe64..d4fb9c8299 100644
--- a/keyboards/handwired/onekey/proton_c/config.h
+++ b/keyboards/handwired/onekey/proton_c/config.h
@@ -21,3 +21,8 @@
 #define MATRIX_COL_PINS { A3 }
 #define MATRIX_ROW_PINS { A2 }
 #define UNUSED_PINS
+
+#define BACKLIGHT_PIN           B8
+#define BACKLIGHT_PWM_DRIVER    PWMD4
+#define BACKLIGHT_PWM_CHANNEL   3
+#define BACKLIGHT_PAL_MODE      2
diff --git a/keyboards/handwired/onekey/stm32f0_disco/config.h b/keyboards/handwired/onekey/stm32f0_disco/config.h
index 039a1beffd..4024ee1caa 100644
--- a/keyboards/handwired/onekey/stm32f0_disco/config.h
+++ b/keyboards/handwired/onekey/stm32f0_disco/config.h
@@ -21,3 +21,8 @@
 #define MATRIX_COL_PINS { B4 }
 #define MATRIX_ROW_PINS { B5 }
 #define UNUSED_PINS
+
+#define BACKLIGHT_PIN           C8
+#define BACKLIGHT_PWM_DRIVER    PWMD3
+#define BACKLIGHT_PWM_CHANNEL   3
+#define BACKLIGHT_PAL_MODE      0
diff --git a/quantum/backlight/backlight.c b/quantum/backlight/backlight.c
new file mode 100644
index 0000000000..e26de86bf9
--- /dev/null
+++ b/quantum/backlight/backlight.c
@@ -0,0 +1 @@
+// TODO: Add common code here, for example cie_lightness implementation
diff --git a/quantum/backlight/backlight_arm.c b/quantum/backlight/backlight_arm.c
new file mode 100644
index 0000000000..3f94ccef8e
--- /dev/null
+++ b/quantum/backlight/backlight_arm.c
@@ -0,0 +1,218 @@
+#include "quantum.h"
+#include "backlight.h"
+#include <hal.h>
+#include "debug.h"
+
+// TODO: remove short term bodge when refactoring BACKLIGHT_CUSTOM_DRIVER out
+#ifdef BACKLIGHT_PIN
+
+#    if defined(STM32F0XX) || defined(STM32F0xx)
+#        error "Backlight support for STMF072 is not available. Please disable."
+#    endif
+
+#    if defined(STM32F1XX) || defined(STM32F1xx)
+#        define USE_GPIOV1
+#    endif
+
+// GPIOV2 && GPIOV3
+#    ifndef BACKLIGHT_PAL_MODE
+#        define BACKLIGHT_PAL_MODE 2
+#    endif
+
+// GENERIC
+#    ifndef BACKLIGHT_PWM_DRIVER
+#        define BACKLIGHT_PWM_DRIVER PWMD4
+#    endif
+#    ifndef BACKLIGHT_PWM_CHANNEL
+#        define BACKLIGHT_PWM_CHANNEL 3
+#    endif
+
+static void breathing_callback(PWMDriver *pwmp);
+
+static PWMConfig pwmCFG = {0xFFFF, /* PWM clock frequency  */
+                           256,    /* PWM period (in ticks) 1S (1/10kHz=0.1mS 0.1ms*10000 ticks=1S) */
+                           NULL,   /* No Callback */
+                           {       /* Default all channels to disabled - Channels will be configured durring init */
+                            {PWM_OUTPUT_DISABLED, NULL},
+                            {PWM_OUTPUT_DISABLED, NULL},
+                            {PWM_OUTPUT_DISABLED, NULL},
+                            {PWM_OUTPUT_DISABLED, NULL}},
+                           0, /* HW dependent part.*/
+                           0};
+
+static PWMConfig pwmCFG_breathing = {0xFFFF,             /** PWM clock frequency  */
+                                     256,                /* PWM period (in ticks) 1S (1/10kHz=0.1mS 0.1ms*10000 ticks=1S) */
+                                     breathing_callback, /* Breathing Callback */
+                                     {                   /* Default all channels to disabled - Channels will be configured durring init */
+                                      {PWM_OUTPUT_DISABLED, NULL},
+                                      {PWM_OUTPUT_DISABLED, NULL},
+                                      {PWM_OUTPUT_DISABLED, NULL},
+                                      {PWM_OUTPUT_DISABLED, NULL}},
+                                     0, /* HW dependent part.*/
+                                     0};
+
+// See http://jared.geek.nz/2013/feb/linear-led-pwm
+static uint16_t cie_lightness(uint16_t v) {
+    if (v <= 5243)     // if below 8% of max
+        return v / 9;  // same as dividing by 900%
+    else {
+        uint32_t y = (((uint32_t)v + 10486) << 8) / (10486 + 0xFFFFUL);  // add 16% of max and compare
+        // to get a useful result with integer division, we shift left in the expression above
+        // and revert what we've done again after squaring.
+        y = y * y * y >> 8;
+        if (y > 0xFFFFUL)  // prevent overflow
+            return 0xFFFFU;
+        else
+            return (uint16_t)y;
+    }
+}
+
+void backlight_init_ports(void) {
+    // printf("backlight_init_ports()\n");
+
+#    ifdef USE_GPIOV1
+    palSetPadMode(PAL_PORT(BACKLIGHT_PIN), PAL_PAD(BACKLIGHT_PIN), PAL_MODE_STM32_ALTERNATE_PUSHPULL);
+#    else
+    palSetPadMode(PAL_PORT(BACKLIGHT_PIN), PAL_PAD(BACKLIGHT_PIN), PAL_MODE_ALTERNATE(BACKLIGHT_PAL_MODE));
+#    endif
+
+    pwmCFG.channels[BACKLIGHT_PWM_CHANNEL - 1].mode           = PWM_OUTPUT_ACTIVE_HIGH;
+    pwmCFG_breathing.channels[BACKLIGHT_PWM_CHANNEL - 1].mode = PWM_OUTPUT_ACTIVE_HIGH;
+    pwmStart(&BACKLIGHT_PWM_DRIVER, &pwmCFG);
+
+    backlight_set(get_backlight_level());
+    if (is_backlight_breathing()) {
+        breathing_enable();
+    }
+}
+
+void backlight_set(uint8_t level) {
+    // printf("backlight_set(%d)\n", level);
+    if (level == 0) {
+        // Turn backlight off
+        pwmDisableChannel(&BACKLIGHT_PWM_DRIVER, BACKLIGHT_PWM_CHANNEL - 1);
+    } else {
+        // Turn backlight on
+        if (!is_breathing()) {
+            uint32_t duty = (uint32_t)(cie_lightness(0xFFFF * (uint32_t)level / BACKLIGHT_LEVELS));
+            // printf("duty: (%d)\n", duty);
+            pwmEnableChannel(&BACKLIGHT_PWM_DRIVER, BACKLIGHT_PWM_CHANNEL - 1, PWM_FRACTION_TO_WIDTH(&BACKLIGHT_PWM_DRIVER, 0xFFFF, duty));
+        }
+    }
+}
+
+uint8_t backlight_tick = 0;
+
+void backlight_task(void) {}
+
+#    define BREATHING_NO_HALT 0
+#    define BREATHING_HALT_OFF 1
+#    define BREATHING_HALT_ON 2
+#    define BREATHING_STEPS 128
+
+static uint8_t  breathing_period  = BREATHING_PERIOD;
+static uint8_t  breathing_halt    = BREATHING_NO_HALT;
+static uint16_t breathing_counter = 0;
+
+bool is_breathing(void) { return BACKLIGHT_PWM_DRIVER.config == &pwmCFG_breathing; }
+
+static inline void breathing_min(void) { breathing_counter = 0; }
+
+static inline void breathing_max(void) { breathing_counter = breathing_period * 256 / 2; }
+
+void breathing_interrupt_enable(void) {
+    pwmStop(&BACKLIGHT_PWM_DRIVER);
+    pwmStart(&BACKLIGHT_PWM_DRIVER, &pwmCFG_breathing);
+    chSysLockFromISR();
+    pwmEnablePeriodicNotification(&BACKLIGHT_PWM_DRIVER);
+    pwmEnableChannelI(&BACKLIGHT_PWM_DRIVER, BACKLIGHT_PWM_CHANNEL - 1, PWM_FRACTION_TO_WIDTH(&BACKLIGHT_PWM_DRIVER, 0xFFFF, 0xFFFF));
+    chSysUnlockFromISR();
+}
+
+void breathing_interrupt_disable(void) {
+    pwmStop(&BACKLIGHT_PWM_DRIVER);
+    pwmStart(&BACKLIGHT_PWM_DRIVER, &pwmCFG);
+}
+
+void breathing_enable(void) {
+    breathing_counter = 0;
+    breathing_halt    = BREATHING_NO_HALT;
+    breathing_interrupt_enable();
+}
+
+void breathing_pulse(void) {
+    if (get_backlight_level() == 0)
+        breathing_min();
+    else
+        breathing_max();
+    breathing_halt = BREATHING_HALT_ON;
+    breathing_interrupt_enable();
+}
+
+void breathing_disable(void) {
+    // printf("breathing_disable()\n");
+    breathing_interrupt_disable();
+    // Restore backlight level
+    backlight_set(get_backlight_level());
+}
+
+void breathing_self_disable(void) {
+    if (get_backlight_level() == 0)
+        breathing_halt = BREATHING_HALT_OFF;
+    else
+        breathing_halt = BREATHING_HALT_ON;
+}
+
+void breathing_toggle(void) {
+    if (is_breathing())
+        breathing_disable();
+    else
+        breathing_enable();
+}
+
+void breathing_period_set(uint8_t value) {
+    if (!value) value = 1;
+    breathing_period = value;
+}
+
+void breathing_period_default(void) { breathing_period_set(BREATHING_PERIOD); }
+
+void breathing_period_inc(void) { breathing_period_set(breathing_period + 1); }
+
+void breathing_period_dec(void) { breathing_period_set(breathing_period - 1); }
+
+/* To generate breathing curve in python:
+ * from math import sin, pi; [int(sin(x/128.0*pi)**4*255) for x in range(128)]
+ */
+static const uint8_t breathing_table[BREATHING_STEPS] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 17, 20, 24, 28, 32, 36, 41, 46, 51, 57, 63, 70, 76, 83, 91, 98, 106, 113, 121, 129, 138, 146, 154, 162, 170, 178, 185, 193, 200, 207, 213, 220, 225, 231, 235, 240, 244, 247, 250, 252, 253, 254, 255, 254, 253, 252, 250, 247, 244, 240, 235, 231, 225, 220, 213, 207, 200, 193, 185, 178, 170, 162, 154, 146, 138, 129, 121, 113, 106, 98, 91, 83, 76, 70, 63, 57, 51, 46, 41, 36, 32, 28, 24, 20, 17, 15, 12, 10, 8, 6, 5, 4, 3, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+
+// Use this before the cie_lightness function.
+static inline uint16_t scale_backlight(uint16_t v) { return v / BACKLIGHT_LEVELS * get_backlight_level(); }
+
+static void breathing_callback(PWMDriver *pwmp) {
+    (void)pwmp;
+    uint16_t interval = (uint16_t)breathing_period * 256 / BREATHING_STEPS;
+    // resetting after one period to prevent ugly reset at overflow.
+    breathing_counter = (breathing_counter + 1) % (breathing_period * 256);
+    uint8_t index     = breathing_counter / interval % BREATHING_STEPS;
+
+    if (((breathing_halt == BREATHING_HALT_ON) && (index == BREATHING_STEPS / 2)) || ((breathing_halt == BREATHING_HALT_OFF) && (index == BREATHING_STEPS - 1))) {
+        breathing_interrupt_disable();
+    }
+
+    uint32_t duty = cie_lightness(scale_backlight(breathing_table[index] * 256));
+
+    chSysLockFromISR();
+    pwmEnableChannelI(&BACKLIGHT_PWM_DRIVER, BACKLIGHT_PWM_CHANNEL - 1, PWM_FRACTION_TO_WIDTH(&BACKLIGHT_PWM_DRIVER, 0xFFFF, duty));
+    chSysUnlockFromISR();
+}
+
+#else
+
+__attribute__((weak)) void backlight_init_ports(void) {}
+
+__attribute__((weak)) void backlight_set(uint8_t level) {}
+
+__attribute__((weak)) void backlight_task(void) {}
+
+#endif
diff --git a/quantum/backlight/backlight_avr.c b/quantum/backlight/backlight_avr.c
new file mode 100644
index 0000000000..445698f47c
--- /dev/null
+++ b/quantum/backlight/backlight_avr.c
@@ -0,0 +1,509 @@
+#include "quantum.h"
+#include "backlight.h"
+#include "debug.h"
+
+#if defined(BACKLIGHT_ENABLE) && (defined(BACKLIGHT_PIN) || defined(BACKLIGHT_PINS))
+
+// This logic is a bit complex, we support 3 setups:
+//
+//   1. Hardware PWM when backlight is wired to a PWM pin.
+//      Depending on this pin, we use a different output compare unit.
+//   2. Software PWM with hardware timers, but the used timer
+//      depends on the Audio setup (Audio wins over Backlight).
+//   3. Full software PWM, driven by the matrix scan, if both timers are used by Audio.
+
+#    if (defined(__AVR_AT90USB646__) || defined(__AVR_AT90USB647__) || defined(__AVR_AT90USB1286__) || defined(__AVR_AT90USB1287__) || defined(__AVR_ATmega16U4__) || defined(__AVR_ATmega32U4__)) && (BACKLIGHT_PIN == B5 || BACKLIGHT_PIN == B6 || BACKLIGHT_PIN == B7)
+#        define HARDWARE_PWM
+#        define ICRx ICR1
+#        define TCCRxA TCCR1A
+#        define TCCRxB TCCR1B
+#        define TIMERx_OVF_vect TIMER1_OVF_vect
+#        define TIMSKx TIMSK1
+#        define TOIEx TOIE1
+
+#        if BACKLIGHT_PIN == B5
+#            define COMxx1 COM1A1
+#            define OCRxx OCR1A
+#        elif BACKLIGHT_PIN == B6
+#            define COMxx1 COM1B1
+#            define OCRxx OCR1B
+#        elif BACKLIGHT_PIN == B7
+#            define COMxx1 COM1C1
+#            define OCRxx OCR1C
+#        endif
+#    elif (defined(__AVR_AT90USB646__) || defined(__AVR_AT90USB647__) || defined(__AVR_AT90USB1286__) || defined(__AVR_AT90USB1287__) || defined(__AVR_ATmega16U4__) || defined(__AVR_ATmega32U4__)) && (BACKLIGHT_PIN == C4 || BACKLIGHT_PIN == C5 || BACKLIGHT_PIN == C6)
+#        define HARDWARE_PWM
+#        define ICRx ICR3
+#        define TCCRxA TCCR3A
+#        define TCCRxB TCCR3B
+#        define TIMERx_OVF_vect TIMER3_OVF_vect
+#        define TIMSKx TIMSK3
+#        define TOIEx TOIE3
+
+#        if BACKLIGHT_PIN == C4
+#            if (defined(__AVR_ATmega16U4__) || defined(__AVR_ATmega32U4__))
+#                error This MCU has no C4 pin!
+#            else
+#                define COMxx1 COM3C1
+#                define OCRxx OCR3C
+#            endif
+#        elif BACKLIGHT_PIN == C5
+#            if (defined(__AVR_ATmega16U4__) || defined(__AVR_ATmega32U4__))
+#                error This MCU has no C5 pin!
+#            else
+#                define COMxx1 COM3B1
+#                define OCRxx OCR3B
+#            endif
+#        elif BACKLIGHT_PIN == C6
+#            define COMxx1 COM3A1
+#            define OCRxx OCR3A
+#        endif
+#    elif (defined(__AVR_ATmega16U2__) || defined(__AVR_ATmega32U2__)) && (BACKLIGHT_PIN == B7 || BACKLIGHT_PIN == C5 || BACKLIGHT_PIN == C6)
+#        define HARDWARE_PWM
+#        define ICRx ICR1
+#        define TCCRxA TCCR1A
+#        define TCCRxB TCCR1B
+#        define TIMERx_OVF_vect TIMER1_OVF_vect
+#        define TIMSKx TIMSK1
+#        define TOIEx TOIE1
+
+#        if BACKLIGHT_PIN == B7
+#            define COMxx1 COM1C1
+#            define OCRxx OCR1C
+#        elif BACKLIGHT_PIN == C5
+#            define COMxx1 COM1B1
+#            define OCRxx OCR1B
+#        elif BACKLIGHT_PIN == C6
+#            define COMxx1 COM1A1
+#            define OCRxx OCR1A
+#        endif
+#    elif defined(__AVR_ATmega32A__) && (BACKLIGHT_PIN == D4 || BACKLIGHT_PIN == D5)
+#        define HARDWARE_PWM
+#        define ICRx ICR1
+#        define TCCRxA TCCR1A
+#        define TCCRxB TCCR1B
+#        define TIMERx_OVF_vect TIMER1_OVF_vect
+#        define TIMSKx TIMSK
+#        define TOIEx TOIE1
+
+#        if BACKLIGHT_PIN == D4
+#            define COMxx1 COM1B1
+#            define OCRxx OCR1B
+#        elif BACKLIGHT_PIN == D5
+#            define COMxx1 COM1A1
+#            define OCRxx OCR1A
+#        endif
+#    elif defined(__AVR_ATmega328P__) && (BACKLIGHT_PIN == B1 || BACKLIGHT_PIN == B2)
+#        define HARDWARE_PWM
+#        define ICRx ICR1
+#        define TCCRxA TCCR1A
+#        define TCCRxB TCCR1B
+#        define TIMERx_OVF_vect TIMER1_OVF_vect
+#        define TIMSKx TIMSK1
+#        define TOIEx TOIE1
+
+#        if BACKLIGHT_PIN == B1
+#            define COMxx1 COM1A1
+#            define OCRxx OCR1A
+#        elif BACKLIGHT_PIN == B2
+#            define COMxx1 COM1B1
+#            define OCRxx OCR1B
+#        endif
+#    else
+#        if !defined(BACKLIGHT_CUSTOM_DRIVER)
+#            if !defined(B5_AUDIO) && !defined(B6_AUDIO) && !defined(B7_AUDIO)
+// Timer 1 is not in use by Audio feature, Backlight can use it
+#                pragma message "Using hardware timer 1 with software PWM"
+#                define HARDWARE_PWM
+#                define BACKLIGHT_PWM_TIMER
+#                define ICRx ICR1
+#                define TCCRxA TCCR1A
+#                define TCCRxB TCCR1B
+#                define TIMERx_COMPA_vect TIMER1_COMPA_vect
+#                define TIMERx_OVF_vect TIMER1_OVF_vect
+#                if defined(__AVR_ATmega32A__)  // This MCU has only one TIMSK register
+#                    define TIMSKx TIMSK
+#                else
+#                    define TIMSKx TIMSK1
+#                endif
+#                define TOIEx TOIE1
+
+#                define OCIExA OCIE1A
+#                define OCRxx OCR1A
+#            elif !defined(C6_AUDIO) && !defined(C5_AUDIO) && !defined(C4_AUDIO)
+#                pragma message "Using hardware timer 3 with software PWM"
+// Timer 3 is not in use by Audio feature, Backlight can use it
+#                define HARDWARE_PWM
+#                define BACKLIGHT_PWM_TIMER
+#                define ICRx ICR1
+#                define TCCRxA TCCR3A
+#                define TCCRxB TCCR3B
+#                define TIMERx_COMPA_vect TIMER3_COMPA_vect
+#                define TIMERx_OVF_vect TIMER3_OVF_vect
+#                define TIMSKx TIMSK3
+#                define TOIEx TOIE3
+
+#                define OCIExA OCIE3A
+#                define OCRxx OCR3A
+#            else
+#                pragma message "Audio in use - using pure software PWM"
+#                define NO_HARDWARE_PWM
+#            endif
+#        else
+#            pragma message "Custom driver defined - using pure software PWM"
+#            define NO_HARDWARE_PWM
+#        endif
+#    endif
+
+#    ifndef BACKLIGHT_ON_STATE
+#        define BACKLIGHT_ON_STATE 0
+#    endif
+
+void backlight_on(uint8_t backlight_pin) {
+#    if BACKLIGHT_ON_STATE == 0
+    writePinLow(backlight_pin);
+#    else
+    writePinHigh(backlight_pin);
+#    endif
+}
+
+void backlight_off(uint8_t backlight_pin) {
+#    if BACKLIGHT_ON_STATE == 0
+    writePinHigh(backlight_pin);
+#    else
+    writePinLow(backlight_pin);
+#    endif
+}
+
+#    if defined(NO_HARDWARE_PWM) || defined(BACKLIGHT_PWM_TIMER)  // pwm through software
+
+// we support multiple backlight pins
+#        ifndef BACKLIGHT_LED_COUNT
+#            define BACKLIGHT_LED_COUNT 1
+#        endif
+
+#        if BACKLIGHT_LED_COUNT == 1
+#            define BACKLIGHT_PIN_INIT \
+                { BACKLIGHT_PIN }
+#        else
+#            define BACKLIGHT_PIN_INIT BACKLIGHT_PINS
+#        endif
+
+#        define FOR_EACH_LED(x)                                 \
+            for (uint8_t i = 0; i < BACKLIGHT_LED_COUNT; i++) { \
+                uint8_t backlight_pin = backlight_pins[i];      \
+                { x }                                           \
+            }
+
+static const uint8_t backlight_pins[BACKLIGHT_LED_COUNT] = BACKLIGHT_PIN_INIT;
+
+#    else  // full hardware PWM
+
+// we support only one backlight pin
+static const uint8_t backlight_pin = BACKLIGHT_PIN;
+#        define FOR_EACH_LED(x) x
+
+#    endif
+
+#    ifdef NO_HARDWARE_PWM
+__attribute__((weak)) void backlight_init_ports(void) {
+    // Setup backlight pin as output and output to on state.
+    FOR_EACH_LED(setPinOutput(backlight_pin); backlight_on(backlight_pin);)
+
+#        ifdef BACKLIGHT_BREATHING
+    if (is_backlight_breathing()) {
+        breathing_enable();
+    }
+#        endif
+}
+
+__attribute__((weak)) void backlight_set(uint8_t level) {}
+
+uint8_t backlight_tick = 0;
+
+#        ifndef BACKLIGHT_CUSTOM_DRIVER
+void backlight_task(void) {
+    if ((0xFFFF >> ((BACKLIGHT_LEVELS - get_backlight_level()) * ((BACKLIGHT_LEVELS + 1) / 2))) & (1 << backlight_tick)) {
+        FOR_EACH_LED(backlight_on(backlight_pin);)
+    } else {
+        FOR_EACH_LED(backlight_off(backlight_pin);)
+    }
+    backlight_tick = (backlight_tick + 1) % 16;
+}
+#        endif
+
+#        ifdef BACKLIGHT_BREATHING
+#            ifndef BACKLIGHT_CUSTOM_DRIVER
+#                error "Backlight breathing only available with hardware PWM. Please disable."
+#            endif
+#        endif
+
+#    else  // hardware pwm through timer
+
+#        ifdef BACKLIGHT_PWM_TIMER
+
+// The idea of software PWM assisted by hardware timers is the following
+// we use the hardware timer in fast PWM mode like for hardware PWM, but
+// instead of letting the Output Match Comparator control the led pin
+// (which is not possible since the backlight is not wired to PWM pins on the
+// CPU), we do the LED on/off by oursleves.
+// The timer is setup to count up to 0xFFFF, and we set the Output Compare
+// register to the current 16bits backlight level (after CIE correction).
+// This means the CPU will trigger a compare match interrupt when the counter
+// reaches the backlight level, where we turn off the LEDs,
+// but also an overflow interrupt when the counter rolls back to 0,
+// in which we're going to turn on the LEDs.
+// The LED will then be on for OCRxx/0xFFFF time, adjusted every 244Hz.
+
+// Triggered when the counter reaches the OCRx value
+ISR(TIMERx_COMPA_vect) { FOR_EACH_LED(backlight_off(backlight_pin);) }
+
+// Triggered when the counter reaches the TOP value
+// this one triggers at F_CPU/65536 =~ 244 Hz
+ISR(TIMERx_OVF_vect) {
+#            ifdef BACKLIGHT_BREATHING
+    if (is_breathing()) {
+        breathing_task();
+    }
+#            endif
+    // for very small values of OCRxx (or backlight level)
+    // we can't guarantee this whole code won't execute
+    // at the same time as the compare match interrupt
+    // which means that we might turn on the leds while
+    // trying to turn them off, leading to flickering
+    // artifacts (especially while breathing, because breathing_task
+    // takes many computation cycles).
+    // so better not turn them on while the counter TOP is very low.
+    if (OCRxx > 256) {
+        FOR_EACH_LED(backlight_on(backlight_pin);)
+    }
+}
+
+#        endif
+
+#        define TIMER_TOP 0xFFFFU
+
+// See http://jared.geek.nz/2013/feb/linear-led-pwm
+static uint16_t cie_lightness(uint16_t v) {
+    if (v <= 5243)     // if below 8% of max
+        return v / 9;  // same as dividing by 900%
+    else {
+        uint32_t y = (((uint32_t)v + 10486) << 8) / (10486 + 0xFFFFUL);  // add 16% of max and compare
+        // to get a useful result with integer division, we shift left in the expression above
+        // and revert what we've done again after squaring.
+        y = y * y * y >> 8;
+        if (y > 0xFFFFUL)  // prevent overflow
+            return 0xFFFFU;
+        else
+            return (uint16_t)y;
+    }
+}
+
+// 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; }
+
+#        ifndef BACKLIGHT_CUSTOM_DRIVER
+__attribute__((weak)) void backlight_set(uint8_t level) {
+    if (level > BACKLIGHT_LEVELS) level = BACKLIGHT_LEVELS;
+
+    if (level == 0) {
+#            ifdef BACKLIGHT_PWM_TIMER
+        if (OCRxx) {
+            TIMSKx &= ~(_BV(OCIExA));
+            TIMSKx &= ~(_BV(TOIEx));
+            FOR_EACH_LED(backlight_off(backlight_pin);)
+        }
+#            else
+        // Turn off PWM control on backlight pin
+        TCCRxA &= ~(_BV(COMxx1));
+#            endif
+    } else {
+#            ifdef BACKLIGHT_PWM_TIMER
+        if (!OCRxx) {
+            TIMSKx |= _BV(OCIExA);
+            TIMSKx |= _BV(TOIEx);
+        }
+#            else
+        // Turn on PWM control of backlight pin
+        TCCRxA |= _BV(COMxx1);
+#            endif
+    }
+    // Set the brightness
+    set_pwm(cie_lightness(TIMER_TOP * (uint32_t)level / BACKLIGHT_LEVELS));
+}
+
+void backlight_task(void) {}
+#        endif  // BACKLIGHT_CUSTOM_DRIVER
+
+#        ifdef BACKLIGHT_BREATHING
+
+#            define BREATHING_NO_HALT 0
+#            define BREATHING_HALT_OFF 1
+#            define BREATHING_HALT_ON 2
+#            define BREATHING_STEPS 128
+
+static uint8_t breathing_period = BREATHING_PERIOD;
+static uint8_t breathing_halt = BREATHING_NO_HALT;
+static uint16_t breathing_counter = 0;
+
+#            ifdef BACKLIGHT_PWM_TIMER
+static bool breathing = false;
+
+bool is_breathing(void) { return breathing; }
+
+#                define breathing_interrupt_enable() \
+                    do {                             \
+                        breathing = true;            \
+                    } while (0)
+#                define breathing_interrupt_disable() \
+                    do {                              \
+                        breathing = false;            \
+                    } while (0)
+#            else
+
+bool is_breathing(void) { return !!(TIMSKx & _BV(TOIEx)); }
+
+#                define breathing_interrupt_enable() \
+                    do {                             \
+                        TIMSKx |= _BV(TOIEx);        \
+                    } while (0)
+#                define breathing_interrupt_disable() \
+                    do {                              \
+                        TIMSKx &= ~_BV(TOIEx);        \
+                    } while (0)
+#            endif
+
+#            define breathing_min()        \
+                do {                       \
+                    breathing_counter = 0; \
+                } while (0)
+#            define breathing_max()                                 \
+                do {                                                \
+                    breathing_counter = breathing_period * 244 / 2; \
+                } while (0)
+
+void breathing_enable(void) {
+    breathing_counter = 0;
+    breathing_halt = BREATHING_NO_HALT;
+    breathing_interrupt_enable();
+}
+
+void breathing_pulse(void) {
+    if (get_backlight_level() == 0)
+        breathing_min();
+    else
+        breathing_max();
+    breathing_halt = BREATHING_HALT_ON;
+    breathing_interrupt_enable();
+}
+
+void breathing_disable(void) {
+    breathing_interrupt_disable();
+    // Restore backlight level
+    backlight_set(get_backlight_level());
+}
+
+void breathing_self_disable(void) {
+    if (get_backlight_level() == 0)
+        breathing_halt = BREATHING_HALT_OFF;
+    else
+        breathing_halt = BREATHING_HALT_ON;
+}
+
+void breathing_toggle(void) {
+    if (is_breathing())
+        breathing_disable();
+    else
+        breathing_enable();
+}
+
+void breathing_period_set(uint8_t value) {
+    if (!value) value = 1;
+    breathing_period = value;
+}
+
+void breathing_period_default(void) { breathing_period_set(BREATHING_PERIOD); }
+
+void breathing_period_inc(void) { breathing_period_set(breathing_period + 1); }
+
+void breathing_period_dec(void) { breathing_period_set(breathing_period - 1); }
+
+/* To generate breathing curve in python:
+ * from math import sin, pi; [int(sin(x/128.0*pi)**4*255) for x in range(128)]
+ */
+static const uint8_t breathing_table[BREATHING_STEPS] PROGMEM = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 17, 20, 24, 28, 32, 36, 41, 46, 51, 57, 63, 70, 76, 83, 91, 98, 106, 113, 121, 129, 138, 146, 154, 162, 170, 178, 185, 193, 200, 207, 213, 220, 225, 231, 235, 240, 244, 247, 250, 252, 253, 254, 255, 254, 253, 252, 250, 247, 244, 240, 235, 231, 225, 220, 213, 207, 200, 193, 185, 178, 170, 162, 154, 146, 138, 129, 121, 113, 106, 98, 91, 83, 76, 70, 63, 57, 51, 46, 41, 36, 32, 28, 24, 20, 17, 15, 12, 10, 8, 6, 5, 4, 3, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+
+// Use this before the cie_lightness function.
+static inline uint16_t scale_backlight(uint16_t v) { return v / BACKLIGHT_LEVELS * get_backlight_level(); }
+
+#            ifdef BACKLIGHT_PWM_TIMER
+void breathing_task(void)
+#            else
+/* Assuming a 16MHz CPU clock and a timer that resets at 64k (ICR1), the following interrupt handler will run
+ * about 244 times per second.
+ */
+ISR(TIMERx_OVF_vect)
+#            endif
+{
+    uint16_t interval = (uint16_t)breathing_period * 244 / BREATHING_STEPS;
+    // resetting after one period to prevent ugly reset at overflow.
+    breathing_counter = (breathing_counter + 1) % (breathing_period * 244);
+    uint8_t index = breathing_counter / interval % BREATHING_STEPS;
+
+    if (((breathing_halt == BREATHING_HALT_ON) && (index == BREATHING_STEPS / 2)) || ((breathing_halt == BREATHING_HALT_OFF) && (index == BREATHING_STEPS - 1))) {
+        breathing_interrupt_disable();
+    }
+
+    set_pwm(cie_lightness(scale_backlight((uint16_t)pgm_read_byte(&breathing_table[index]) * 0x0101U)));
+}
+
+#        endif  // BACKLIGHT_BREATHING
+
+__attribute__((weak)) void backlight_init_ports(void) {
+    // Setup backlight pin as output and output to on state.
+    FOR_EACH_LED(setPinOutput(backlight_pin); backlight_on(backlight_pin);)
+
+    // I could write a wall of text here to explain... but TL;DW
+    // Go read the ATmega32u4 datasheet.
+    // And this: http://blog.saikoled.com/post/43165849837/secret-konami-cheat-code-to-high-resolution-pwm-on
+
+#        ifdef BACKLIGHT_PWM_TIMER
+    // TimerX setup, Fast PWM mode count to TOP set in ICRx
+    TCCRxA = _BV(WGM11);  // = 0b00000010;
+    // clock select clk/1
+    TCCRxB = _BV(WGM13) | _BV(WGM12) | _BV(CS10);  // = 0b00011001;
+#        else  // hardware PWM
+    // Pin PB7 = OCR1C (Timer 1, Channel C)
+    // Compare Output Mode = Clear on compare match, Channel C = COM1C1=1 COM1C0=0
+    // (i.e. start high, go low when counter matches.)
+    // WGM Mode 14 (Fast PWM) = WGM13=1 WGM12=1 WGM11=1 WGM10=0
+    // Clock Select = clk/1 (no prescaling) = CS12=0 CS11=0 CS10=1
+
+    /*
+    14.8.3:
+    "In fast PWM mode, the compare units allow generation of PWM waveforms on the OCnx pins. Setting the COMnx1:0 bits to two will produce a non-inverted PWM [..]."
+    "In fast PWM mode the counter is incremented until the counter value matches either one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGMn3:0 = 5, 6, or 7), the value in ICRn (WGMn3:0 = 14), or the value in OCRnA (WGMn3:0 = 15)."
+    */
+    TCCRxA = _BV(COMxx1) | _BV(WGM11);             // = 0b00001010;
+    TCCRxB = _BV(WGM13) | _BV(WGM12) | _BV(CS10);  // = 0b00011001;
+#        endif
+    // Use full 16-bit resolution. Counter counts to ICR1 before reset to 0.
+    ICRx = TIMER_TOP;
+
+    backlight_init();
+#        ifdef BACKLIGHT_BREATHING
+    if (is_backlight_breathing()) {
+        breathing_enable();
+    }
+#        endif
+}
+
+#    endif  // hardware backlight
+
+#else  // no backlight
+
+__attribute__((weak)) void backlight_init_ports(void) {}
+
+__attribute__((weak)) void backlight_set(uint8_t level) {}
+
+#endif  // backlight
\ No newline at end of file
diff --git a/quantum/quantum.c b/quantum/quantum.c
index 16922dd011..f4999456e3 100644
--- a/quantum/quantum.c
+++ b/quantum/quantum.c
@@ -24,10 +24,6 @@
 #    include "outputselect.h"
 #endif
 
-#ifndef BREATHING_PERIOD
-#    define BREATHING_PERIOD 6
-#endif
-
 #include "backlight.h"
 extern backlight_config_t backlight_config;
 
@@ -1019,511 +1015,6 @@ void matrix_scan_quantum() {
 
     matrix_scan_kb();
 }
-#if defined(BACKLIGHT_ENABLE) && (defined(BACKLIGHT_PIN) || defined(BACKLIGHT_PINS))
-
-// This logic is a bit complex, we support 3 setups:
-//
-//   1. Hardware PWM when backlight is wired to a PWM pin.
-//      Depending on this pin, we use a different output compare unit.
-//   2. Software PWM with hardware timers, but the used timer
-//      depends on the Audio setup (Audio wins over Backlight).
-//   3. Full software PWM, driven by the matrix scan, if both timers are used by Audio.
-
-#    if (defined(__AVR_AT90USB646__) || defined(__AVR_AT90USB647__) || defined(__AVR_AT90USB1286__) || defined(__AVR_AT90USB1287__) || defined(__AVR_ATmega16U4__) || defined(__AVR_ATmega32U4__)) && (BACKLIGHT_PIN == B5 || BACKLIGHT_PIN == B6 || BACKLIGHT_PIN == B7)
-#        define HARDWARE_PWM
-#        define ICRx ICR1
-#        define TCCRxA TCCR1A
-#        define TCCRxB TCCR1B
-#        define TIMERx_OVF_vect TIMER1_OVF_vect
-#        define TIMSKx TIMSK1
-#        define TOIEx TOIE1
-
-#        if BACKLIGHT_PIN == B5
-#            define COMxx1 COM1A1
-#            define OCRxx OCR1A
-#        elif BACKLIGHT_PIN == B6
-#            define COMxx1 COM1B1
-#            define OCRxx OCR1B
-#        elif BACKLIGHT_PIN == B7
-#            define COMxx1 COM1C1
-#            define OCRxx OCR1C
-#        endif
-#    elif (defined(__AVR_AT90USB646__) || defined(__AVR_AT90USB647__) || defined(__AVR_AT90USB1286__) || defined(__AVR_AT90USB1287__) || defined(__AVR_ATmega16U4__) || defined(__AVR_ATmega32U4__)) && (BACKLIGHT_PIN == C4 || BACKLIGHT_PIN == C5 || BACKLIGHT_PIN == C6)
-#        define HARDWARE_PWM
-#        define ICRx ICR3
-#        define TCCRxA TCCR3A
-#        define TCCRxB TCCR3B
-#        define TIMERx_OVF_vect TIMER3_OVF_vect
-#        define TIMSKx TIMSK3
-#        define TOIEx TOIE3
-
-#        if BACKLIGHT_PIN == C4
-#            if (defined(__AVR_ATmega16U4__) || defined(__AVR_ATmega32U4__))
-#                error This MCU has no C4 pin!
-#            else
-#                define COMxx1 COM3C1
-#                define OCRxx OCR3C
-#            endif
-#        elif BACKLIGHT_PIN == C5
-#            if (defined(__AVR_ATmega16U4__) || defined(__AVR_ATmega32U4__))
-#                error This MCU has no C5 pin!
-#            else
-#                define COMxx1 COM3B1
-#                define OCRxx OCR3B
-#            endif
-#        elif BACKLIGHT_PIN == C6
-#            define COMxx1 COM3A1
-#            define OCRxx OCR3A
-#        endif
-#    elif (defined(__AVR_ATmega16U2__) || defined(__AVR_ATmega32U2__)) && (BACKLIGHT_PIN == B7 || BACKLIGHT_PIN == C5 || BACKLIGHT_PIN == C6)
-#        define HARDWARE_PWM
-#        define ICRx ICR1
-#        define TCCRxA TCCR1A
-#        define TCCRxB TCCR1B
-#        define TIMERx_OVF_vect TIMER1_OVF_vect
-#        define TIMSKx TIMSK1
-#        define TOIEx TOIE1
-
-#        if BACKLIGHT_PIN == B7
-#            define COMxx1 COM1C1
-#            define OCRxx OCR1C
-#        elif BACKLIGHT_PIN == C5
-#            define COMxx1 COM1B1
-#            define OCRxx OCR1B
-#        elif BACKLIGHT_PIN == C6
-#            define COMxx1 COM1A1
-#            define OCRxx OCR1A
-#        endif
-#    elif defined(__AVR_ATmega32A__) && (BACKLIGHT_PIN == D4 || BACKLIGHT_PIN == D5)
-#        define HARDWARE_PWM
-#        define ICRx ICR1
-#        define TCCRxA TCCR1A
-#        define TCCRxB TCCR1B
-#        define TIMERx_OVF_vect TIMER1_OVF_vect
-#        define TIMSKx TIMSK
-#        define TOIEx TOIE1
-
-#        if BACKLIGHT_PIN == D4
-#            define COMxx1 COM1B1
-#            define OCRxx OCR1B
-#        elif BACKLIGHT_PIN == D5
-#            define COMxx1 COM1A1
-#            define OCRxx OCR1A
-#        endif
-#    elif defined(__AVR_ATmega328P__) && (BACKLIGHT_PIN == B1 || BACKLIGHT_PIN == B2)
-#        define HARDWARE_PWM
-#        define ICRx ICR1
-#        define TCCRxA TCCR1A
-#        define TCCRxB TCCR1B
-#        define TIMERx_OVF_vect TIMER1_OVF_vect
-#        define TIMSKx TIMSK1
-#        define TOIEx TOIE1
-
-#        if BACKLIGHT_PIN == B1
-#            define COMxx1 COM1A1
-#            define OCRxx OCR1A
-#        elif BACKLIGHT_PIN == B2
-#            define COMxx1 COM1B1
-#            define OCRxx OCR1B
-#        endif
-#    else
-#        if !defined(BACKLIGHT_CUSTOM_DRIVER)
-#            if !defined(B5_AUDIO) && !defined(B6_AUDIO) && !defined(B7_AUDIO)
-// Timer 1 is not in use by Audio feature, Backlight can use it
-#                pragma message "Using hardware timer 1 with software PWM"
-#                define HARDWARE_PWM
-#                define BACKLIGHT_PWM_TIMER
-#                define ICRx ICR1
-#                define TCCRxA TCCR1A
-#                define TCCRxB TCCR1B
-#                define TIMERx_COMPA_vect TIMER1_COMPA_vect
-#                define TIMERx_OVF_vect TIMER1_OVF_vect
-#                if defined(__AVR_ATmega32A__)  // This MCU has only one TIMSK register
-#                    define TIMSKx TIMSK
-#                else
-#                    define TIMSKx TIMSK1
-#                endif
-#                define TOIEx TOIE1
-
-#                define OCIExA OCIE1A
-#                define OCRxx OCR1A
-#            elif !defined(C6_AUDIO) && !defined(C5_AUDIO) && !defined(C4_AUDIO)
-#                pragma message "Using hardware timer 3 with software PWM"
-// Timer 3 is not in use by Audio feature, Backlight can use it
-#                define HARDWARE_PWM
-#                define BACKLIGHT_PWM_TIMER
-#                define ICRx ICR1
-#                define TCCRxA TCCR3A
-#                define TCCRxB TCCR3B
-#                define TIMERx_COMPA_vect TIMER3_COMPA_vect
-#                define TIMERx_OVF_vect TIMER3_OVF_vect
-#                define TIMSKx TIMSK3
-#                define TOIEx TOIE3
-
-#                define OCIExA OCIE3A
-#                define OCRxx OCR3A
-#            else
-#                pragma message "Audio in use - using pure software PWM"
-#                define NO_HARDWARE_PWM
-#            endif
-#        else
-#            pragma message "Custom driver defined - using pure software PWM"
-#            define NO_HARDWARE_PWM
-#        endif
-#    endif
-
-#    ifndef BACKLIGHT_ON_STATE
-#        define BACKLIGHT_ON_STATE 0
-#    endif
-
-void backlight_on(uint8_t backlight_pin) {
-#    if BACKLIGHT_ON_STATE == 0
-    writePinLow(backlight_pin);
-#    else
-    writePinHigh(backlight_pin);
-#    endif
-}
-
-void backlight_off(uint8_t backlight_pin) {
-#    if BACKLIGHT_ON_STATE == 0
-    writePinHigh(backlight_pin);
-#    else
-    writePinLow(backlight_pin);
-#    endif
-}
-
-#    if defined(NO_HARDWARE_PWM) || defined(BACKLIGHT_PWM_TIMER)  // pwm through software
-
-// we support multiple backlight pins
-#        ifndef BACKLIGHT_LED_COUNT
-#            define BACKLIGHT_LED_COUNT 1
-#        endif
-
-#        if BACKLIGHT_LED_COUNT == 1
-#            define BACKLIGHT_PIN_INIT \
-                { BACKLIGHT_PIN }
-#        else
-#            define BACKLIGHT_PIN_INIT BACKLIGHT_PINS
-#        endif
-
-#        define FOR_EACH_LED(x)                                 \
-            for (uint8_t i = 0; i < BACKLIGHT_LED_COUNT; i++) { \
-                uint8_t backlight_pin = backlight_pins[i];      \
-                { x }                                           \
-            }
-
-static const uint8_t backlight_pins[BACKLIGHT_LED_COUNT] = BACKLIGHT_PIN_INIT;
-
-#    else  // full hardware PWM
-
-// we support only one backlight pin
-static const uint8_t backlight_pin = BACKLIGHT_PIN;
-#        define FOR_EACH_LED(x) x
-
-#    endif
-
-#    ifdef NO_HARDWARE_PWM
-__attribute__((weak)) void backlight_init_ports(void) {
-    // Setup backlight pin as output and output to on state.
-    FOR_EACH_LED(setPinOutput(backlight_pin); backlight_on(backlight_pin);)
-
-#        ifdef BACKLIGHT_BREATHING
-    if (is_backlight_breathing()) {
-        breathing_enable();
-    }
-#        endif
-}
-
-__attribute__((weak)) void backlight_set(uint8_t level) {}
-
-uint8_t backlight_tick = 0;
-
-#        ifndef BACKLIGHT_CUSTOM_DRIVER
-void backlight_task(void) {
-    if ((0xFFFF >> ((BACKLIGHT_LEVELS - get_backlight_level()) * ((BACKLIGHT_LEVELS + 1) / 2))) & (1 << backlight_tick)) {
-        FOR_EACH_LED(backlight_on(backlight_pin);)
-    } else {
-        FOR_EACH_LED(backlight_off(backlight_pin);)
-    }
-    backlight_tick = (backlight_tick + 1) % 16;
-}
-#        endif
-
-#        ifdef BACKLIGHT_BREATHING
-#            ifndef BACKLIGHT_CUSTOM_DRIVER
-#                error "Backlight breathing only available with hardware PWM. Please disable."
-#            endif
-#        endif
-
-#    else  // hardware pwm through timer
-
-#        ifdef BACKLIGHT_PWM_TIMER
-
-// The idea of software PWM assisted by hardware timers is the following
-// we use the hardware timer in fast PWM mode like for hardware PWM, but
-// instead of letting the Output Match Comparator control the led pin
-// (which is not possible since the backlight is not wired to PWM pins on the
-// CPU), we do the LED on/off by oursleves.
-// The timer is setup to count up to 0xFFFF, and we set the Output Compare
-// register to the current 16bits backlight level (after CIE correction).
-// This means the CPU will trigger a compare match interrupt when the counter
-// reaches the backlight level, where we turn off the LEDs,
-// but also an overflow interrupt when the counter rolls back to 0,
-// in which we're going to turn on the LEDs.
-// The LED will then be on for OCRxx/0xFFFF time, adjusted every 244Hz.
-
-// Triggered when the counter reaches the OCRx value
-ISR(TIMERx_COMPA_vect) { FOR_EACH_LED(backlight_off(backlight_pin);) }
-
-// Triggered when the counter reaches the TOP value
-// this one triggers at F_CPU/65536 =~ 244 Hz
-ISR(TIMERx_OVF_vect) {
-#            ifdef BACKLIGHT_BREATHING
-    if (is_breathing()) {
-        breathing_task();
-    }
-#            endif
-    // for very small values of OCRxx (or backlight level)
-    // we can't guarantee this whole code won't execute
-    // at the same time as the compare match interrupt
-    // which means that we might turn on the leds while
-    // trying to turn them off, leading to flickering
-    // artifacts (especially while breathing, because breathing_task
-    // takes many computation cycles).
-    // so better not turn them on while the counter TOP is very low.
-    if (OCRxx > 256) {
-        FOR_EACH_LED(backlight_on(backlight_pin);)
-    }
-}
-
-#        endif
-
-#        define TIMER_TOP 0xFFFFU
-
-// See http://jared.geek.nz/2013/feb/linear-led-pwm
-static uint16_t cie_lightness(uint16_t v) {
-    if (v <= 5243)     // if below 8% of max
-        return v / 9;  // same as dividing by 900%
-    else {
-        uint32_t y = (((uint32_t)v + 10486) << 8) / (10486 + 0xFFFFUL);  // add 16% of max and compare
-        // to get a useful result with integer division, we shift left in the expression above
-        // and revert what we've done again after squaring.
-        y = y * y * y >> 8;
-        if (y > 0xFFFFUL)  // prevent overflow
-            return 0xFFFFU;
-        else
-            return (uint16_t)y;
-    }
-}
-
-// 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; }
-
-#        ifndef BACKLIGHT_CUSTOM_DRIVER
-__attribute__((weak)) void backlight_set(uint8_t level) {
-    if (level > BACKLIGHT_LEVELS) level = BACKLIGHT_LEVELS;
-
-    if (level == 0) {
-#            ifdef BACKLIGHT_PWM_TIMER
-        if (OCRxx) {
-            TIMSKx &= ~(_BV(OCIExA));
-            TIMSKx &= ~(_BV(TOIEx));
-            FOR_EACH_LED(backlight_off(backlight_pin);)
-        }
-#            else
-        // Turn off PWM control on backlight pin
-        TCCRxA &= ~(_BV(COMxx1));
-#            endif
-    } else {
-#            ifdef BACKLIGHT_PWM_TIMER
-        if (!OCRxx) {
-            TIMSKx |= _BV(OCIExA);
-            TIMSKx |= _BV(TOIEx);
-        }
-#            else
-        // Turn on PWM control of backlight pin
-        TCCRxA |= _BV(COMxx1);
-#            endif
-    }
-    // Set the brightness
-    set_pwm(cie_lightness(TIMER_TOP * (uint32_t)level / BACKLIGHT_LEVELS));
-}
-
-void backlight_task(void) {}
-#        endif  // BACKLIGHT_CUSTOM_DRIVER
-
-#        ifdef BACKLIGHT_BREATHING
-
-#            define BREATHING_NO_HALT 0
-#            define BREATHING_HALT_OFF 1
-#            define BREATHING_HALT_ON 2
-#            define BREATHING_STEPS 128
-
-static uint8_t breathing_period = BREATHING_PERIOD;
-static uint8_t breathing_halt = BREATHING_NO_HALT;
-static uint16_t breathing_counter = 0;
-
-#            ifdef BACKLIGHT_PWM_TIMER
-static bool breathing = false;
-
-bool is_breathing(void) { return breathing; }
-
-#                define breathing_interrupt_enable() \
-                    do {                             \
-                        breathing = true;            \
-                    } while (0)
-#                define breathing_interrupt_disable() \
-                    do {                              \
-                        breathing = false;            \
-                    } while (0)
-#            else
-
-bool is_breathing(void) { return !!(TIMSKx & _BV(TOIEx)); }
-
-#                define breathing_interrupt_enable() \
-                    do {                             \
-                        TIMSKx |= _BV(TOIEx);        \
-                    } while (0)
-#                define breathing_interrupt_disable() \
-                    do {                              \
-                        TIMSKx &= ~_BV(TOIEx);        \
-                    } while (0)
-#            endif
-
-#            define breathing_min()        \
-                do {                       \
-                    breathing_counter = 0; \
-                } while (0)
-#            define breathing_max()                                 \
-                do {                                                \
-                    breathing_counter = breathing_period * 244 / 2; \
-                } while (0)
-
-void breathing_enable(void) {
-    breathing_counter = 0;
-    breathing_halt = BREATHING_NO_HALT;
-    breathing_interrupt_enable();
-}
-
-void breathing_pulse(void) {
-    if (get_backlight_level() == 0)
-        breathing_min();
-    else
-        breathing_max();
-    breathing_halt = BREATHING_HALT_ON;
-    breathing_interrupt_enable();
-}
-
-void breathing_disable(void) {
-    breathing_interrupt_disable();
-    // Restore backlight level
-    backlight_set(get_backlight_level());
-}
-
-void breathing_self_disable(void) {
-    if (get_backlight_level() == 0)
-        breathing_halt = BREATHING_HALT_OFF;
-    else
-        breathing_halt = BREATHING_HALT_ON;
-}
-
-void breathing_toggle(void) {
-    if (is_breathing())
-        breathing_disable();
-    else
-        breathing_enable();
-}
-
-void breathing_period_set(uint8_t value) {
-    if (!value) value = 1;
-    breathing_period = value;
-}
-
-void breathing_period_default(void) { breathing_period_set(BREATHING_PERIOD); }
-
-void breathing_period_inc(void) { breathing_period_set(breathing_period + 1); }
-
-void breathing_period_dec(void) { breathing_period_set(breathing_period - 1); }
-
-/* To generate breathing curve in python:
- * from math import sin, pi; [int(sin(x/128.0*pi)**4*255) for x in range(128)]
- */
-static const uint8_t breathing_table[BREATHING_STEPS] PROGMEM = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 17, 20, 24, 28, 32, 36, 41, 46, 51, 57, 63, 70, 76, 83, 91, 98, 106, 113, 121, 129, 138, 146, 154, 162, 170, 178, 185, 193, 200, 207, 213, 220, 225, 231, 235, 240, 244, 247, 250, 252, 253, 254, 255, 254, 253, 252, 250, 247, 244, 240, 235, 231, 225, 220, 213, 207, 200, 193, 185, 178, 170, 162, 154, 146, 138, 129, 121, 113, 106, 98, 91, 83, 76, 70, 63, 57, 51, 46, 41, 36, 32, 28, 24, 20, 17, 15, 12, 10, 8, 6, 5, 4, 3, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
-
-// Use this before the cie_lightness function.
-static inline uint16_t scale_backlight(uint16_t v) { return v / BACKLIGHT_LEVELS * get_backlight_level(); }
-
-#            ifdef BACKLIGHT_PWM_TIMER
-void breathing_task(void)
-#            else
-/* Assuming a 16MHz CPU clock and a timer that resets at 64k (ICR1), the following interrupt handler will run
- * about 244 times per second.
- */
-ISR(TIMERx_OVF_vect)
-#            endif
-{
-    uint16_t interval = (uint16_t)breathing_period * 244 / BREATHING_STEPS;
-    // resetting after one period to prevent ugly reset at overflow.
-    breathing_counter = (breathing_counter + 1) % (breathing_period * 244);
-    uint8_t index = breathing_counter / interval % BREATHING_STEPS;
-
-    if (((breathing_halt == BREATHING_HALT_ON) && (index == BREATHING_STEPS / 2)) || ((breathing_halt == BREATHING_HALT_OFF) && (index == BREATHING_STEPS - 1))) {
-        breathing_interrupt_disable();
-    }
-
-    set_pwm(cie_lightness(scale_backlight((uint16_t)pgm_read_byte(&breathing_table[index]) * 0x0101U)));
-}
-
-#        endif  // BACKLIGHT_BREATHING
-
-__attribute__((weak)) void backlight_init_ports(void) {
-    // Setup backlight pin as output and output to on state.
-    FOR_EACH_LED(setPinOutput(backlight_pin); backlight_on(backlight_pin);)
-
-    // I could write a wall of text here to explain... but TL;DW
-    // Go read the ATmega32u4 datasheet.
-    // And this: http://blog.saikoled.com/post/43165849837/secret-konami-cheat-code-to-high-resolution-pwm-on
-
-#        ifdef BACKLIGHT_PWM_TIMER
-    // TimerX setup, Fast PWM mode count to TOP set in ICRx
-    TCCRxA = _BV(WGM11);  // = 0b00000010;
-    // clock select clk/1
-    TCCRxB = _BV(WGM13) | _BV(WGM12) | _BV(CS10);  // = 0b00011001;
-#        else  // hardware PWM
-    // Pin PB7 = OCR1C (Timer 1, Channel C)
-    // Compare Output Mode = Clear on compare match, Channel C = COM1C1=1 COM1C0=0
-    // (i.e. start high, go low when counter matches.)
-    // WGM Mode 14 (Fast PWM) = WGM13=1 WGM12=1 WGM11=1 WGM10=0
-    // Clock Select = clk/1 (no prescaling) = CS12=0 CS11=0 CS10=1
-
-    /*
-    14.8.3:
-    "In fast PWM mode, the compare units allow generation of PWM waveforms on the OCnx pins. Setting the COMnx1:0 bits to two will produce a non-inverted PWM [..]."
-    "In fast PWM mode the counter is incremented until the counter value matches either one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGMn3:0 = 5, 6, or 7), the value in ICRn (WGMn3:0 = 14), or the value in OCRnA (WGMn3:0 = 15)."
-    */
-    TCCRxA = _BV(COMxx1) | _BV(WGM11);             // = 0b00001010;
-    TCCRxB = _BV(WGM13) | _BV(WGM12) | _BV(CS10);  // = 0b00011001;
-#        endif
-    // Use full 16-bit resolution. Counter counts to ICR1 before reset to 0.
-    ICRx = TIMER_TOP;
-
-    backlight_init();
-#        ifdef BACKLIGHT_BREATHING
-    if (is_backlight_breathing()) {
-        breathing_enable();
-    }
-#        endif
-}
-
-#    endif  // hardware backlight
-
-#else  // no backlight
-
-__attribute__((weak)) void backlight_init_ports(void) {}
-
-__attribute__((weak)) void backlight_set(uint8_t level) {}
-
-#endif  // backlight
 
 #ifdef HD44780_ENABLED
 #    include "hd44780.h"
diff --git a/tmk_core/common/backlight.h b/tmk_core/common/backlight.h
index bb1f897ee8..1e581055db 100644
--- a/tmk_core/common/backlight.h
+++ b/tmk_core/common/backlight.h
@@ -26,6 +26,10 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #    error "Maximum value of BACKLIGHT_LEVELS is 31"
 #endif
 
+#ifndef BREATHING_PERIOD
+#    define BREATHING_PERIOD 6
+#endif
+
 typedef union {
     uint8_t raw;
     struct {