Smooth brightness transitions with pwm backlight

src/components/brightness/BrightnessController.cpp

@@ -2,39 +2,75 @@
 #include <hal/nrf_gpio.h>
 #include "displayapp/screens/Symbols.h"
 #include "drivers/PinMap.h"
+
+#include "nrf_pwm.h"
+
 using namespace Pinetime::Controllers;
 
 void BrightnessController::Init() {
   nrf_gpio_cfg_output(PinMap::LcdBacklightLow);
   nrf_gpio_cfg_output(PinMap::LcdBacklightMedium);
   nrf_gpio_cfg_output(PinMap::LcdBacklightHigh);
+
+  nrf_gpio_pin_clear(PinMap::LcdBacklightLow);
+  nrf_gpio_pin_clear(PinMap::LcdBacklightMedium);
+  nrf_gpio_pin_clear(PinMap::LcdBacklightHigh);
+
+  static nrf_pwm_sequence_t seq;
+
+  seq.values.p_common = pwmSequence;
+  seq.length          = 1;
+  seq.repeats         = 0;
+  seq.end_delay       = 0;
+
+  uint32_t out_pins[] = {PinMap::LcdBacklightHigh, PinMap::LcdBacklightMedium, PinMap::LcdBacklightLow, NRF_PWM_PIN_NOT_CONNECTED};
+
+  nrf_pwm_pins_set(NRF_PWM0, out_pins);
+  nrf_pwm_enable(NRF_PWM0);
+  // With 8 MHz and 10000 reload timer PWM frequency is 712 Hz
+  nrf_pwm_configure(NRF_PWM0, NRF_PWM_CLK_8MHz, NRF_PWM_MODE_UP, 10000);
+  nrf_pwm_loop_set(NRF_PWM0, 0);
+  nrf_pwm_decoder_set(NRF_PWM0, NRF_PWM_LOAD_COMMON, NRF_PWM_STEP_AUTO);
+  nrf_pwm_sequence_set(NRF_PWM0, 0, &seq);
+  nrf_pwm_task_trigger(NRF_PWM0, NRF_PWM_TASK_SEQSTART0);
+
+  pwmVal = 0;
   Set(level);
-}
+};
 
-void BrightnessController::Set(BrightnessController::Levels level) {
+void BrightnessController::setPwm(uint16_t val) {
+  pwmSequence[0] = val;
+  nrf_pwm_task_trigger(NRF_PWM0, NRF_PWM_TASK_SEQSTART0);
+};
+
+uint16_t BrightnessController::getPwm(BrightnessController::Levels level) {
   this->level = level;
   switch (level) {
     default:
     case Levels::High:
-      nrf_gpio_pin_clear(PinMap::LcdBacklightLow);
-      nrf_gpio_pin_clear(PinMap::LcdBacklightMedium);
-      nrf_gpio_pin_clear(PinMap::LcdBacklightHigh);
-      break;
+      return 10000;
     case Levels::Medium:
-      nrf_gpio_pin_clear(PinMap::LcdBacklightLow);
-      nrf_gpio_pin_clear(PinMap::LcdBacklightMedium);
-      nrf_gpio_pin_set(PinMap::LcdBacklightHigh);
-      break;
+      return 4000;
     case Levels::Low:
-      nrf_gpio_pin_clear(PinMap::LcdBacklightLow);
-      nrf_gpio_pin_set(PinMap::LcdBacklightMedium);
-      nrf_gpio_pin_set(PinMap::LcdBacklightHigh);
-      break;
+      return 900;
     case Levels::Off:
-      nrf_gpio_pin_set(PinMap::LcdBacklightLow);
-      nrf_gpio_pin_set(PinMap::LcdBacklightMedium);
-      nrf_gpio_pin_set(PinMap::LcdBacklightHigh);
-      break;
+      return 0;
+  }
+}
+
+void BrightnessController::Set(BrightnessController::Levels level) {
+  this->level = level;
+  uint16_t target = getPwm(level);
+  uint16_t step = abs((pwmVal - target) / 10);
+
+  while (target != pwmVal) {
+    if (target > pwmVal) {
+      pwmVal += step;
+    } else {
+      pwmVal -= step;
+    }
+    setPwm(pwmVal);
+    vTaskDelay(20);
   }
 }
 

src/components/brightness/BrightnessController.h

@@ -1,6 +1,9 @@
 #pragma once
 
 #include <cstdint>
+#include <cmath>
+#include <FreeRTOS.h>
+#include <task.h>
 
 namespace Pinetime {
   namespace Controllers {
@@ -20,6 +23,10 @@ namespace Pinetime {
 
     private:
       Levels level = Levels::High;
+      uint16_t pwmVal;
+      uint16_t getPwm(Levels level);
+      void setPwm(uint16_t val);
+      uint16_t pwmSequence[1] = {10000};
     };
   }
 }

src/displayapp/DisplayApp.cpp

@@ -221,10 +221,7 @@ void DisplayApp::Refresh() {
         RestoreBrightness();
         break;
       case Messages::GoToSleep:
-        while (brightnessController.Level() != Controllers::BrightnessController::Levels::Off) {
-          brightnessController.Lower();
-          vTaskDelay(100);
-        }
+	brightnessController.Set(Controllers::BrightnessController::Levels::Off);
         lcd.Sleep();
         PushMessageToSystemTask(Pinetime::System::Messages::OnDisplayTaskSleeping);
         state = States::Idle;