Rescale both ChibiOS and AVR backlighting.

docs/feature_backlight.md

@@ -62,14 +62,15 @@ Valid driver values are `pwm`, `software`, `custom` or `no`. See below for help
 
 To configure the backlighting, `#define` these in your `config.h`:
 
-|Define               |Default      |Description                                                                          |
-|---------------------|-------------|-------------------------------------------------------------------------------------|
-|`BACKLIGHT_PIN`      |*Not defined*|The pin that controls the LED(s)                                                     |
-|`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_ON_STATE` |`1`          |The state of the backlight pin when the backlight is "on" - `1` for high, `0` for low|
+| Define                 | Default       | Description                                                                                                       |
+|------------------------|---------------|-------------------------------------------------------------------------------------------------------------------|
+| `BACKLIGHT_PIN`        | *Not defined* | The pin that controls the LED(s)                                                                                  |
+| `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_ON_STATE`   | `1`           | The state of the backlight pin when the backlight is "on" - `1` for high, `0` for low                             |
+| `BACKLIGHT_LIMIT_VAL ` | `255`         | The maximum duty cycle of the backlight -- `255` allows for full brightness, any lower will decrease the maximum. |
 
 Unless you are designing your own keyboard, you generally should not need to change the `BACKLIGHT_PIN` or `BACKLIGHT_ON_STATE`.
 

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 +245,11 @@ 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 +279,7 @@ 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 +385,7 @@ 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

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));