ARM backlight - timer implementation (#8291)

* Add GPT timer based backlight driver

* Update to tim15 to avoid conflict with audio

* Update quantum/backlight/backlight_timer.c

3 files changed, 169 insertions, 2 deletions

diff --git a/common_features.mk b/common_features.mk
index 43df3827b1..855ee8cea1 100644
--- a/common_features.mk
+++ b/common_features.mk
@@ -263,7 +263,7 @@ ifeq ($(strip $(BACKLIGHT_CUSTOM_DRIVER)), yes)
     BACKLIGHT_DRIVER := custom
 endif
 
-VALID_BACKLIGHT_TYPES := pwm software custom
+VALID_BACKLIGHT_TYPES := pwm timer software custom
 
 BACKLIGHT_ENABLE ?= no
 BACKLIGHT_DRIVER ?= pwm
diff --git a/platforms/chibios/GENERIC_STM32_F303XC/configs/mcuconf.h b/platforms/chibios/GENERIC_STM32_F303XC/configs/mcuconf.h
index 3b15883485..ac2d9a1eed 100644
--- a/platforms/chibios/GENERIC_STM32_F303XC/configs/mcuconf.h
+++ b/platforms/chibios/GENERIC_STM32_F303XC/configs/mcuconf.h
@@ -144,7 +144,7 @@
 #define STM32_GPT_USE_TIM6                  TRUE
 #define STM32_GPT_USE_TIM7                  TRUE
 #define STM32_GPT_USE_TIM8                  TRUE
-#define STM32_GPT_USE_TIM15                 FALSE
+#define STM32_GPT_USE_TIM15                 TRUE
 #define STM32_GPT_USE_TIM16                 FALSE
 #define STM32_GPT_USE_TIM17                 FALSE
 #define STM32_GPT_TIM1_IRQ_PRIORITY         7
diff --git a/quantum/backlight/backlight_timer.c b/quantum/backlight/backlight_timer.c
new file mode 100644
index 0000000000..c32c35c154
--- /dev/null
+++ b/quantum/backlight/backlight_timer.c
@@ -0,0 +1,167 @@
+#include "quantum.h"
+#include "backlight.h"
+#include "backlight_driver_common.h"
+#include "debug.h"
+
+#ifndef BACKLIGHT_GPT_DRIVER
+#    define BACKLIGHT_GPT_DRIVER GPTD15
+#endif
+
+// Platform specific implementations
+static void     backlight_timer_configure(bool enable);
+static void     backlight_timer_set_duty(uint16_t duty);
+static uint16_t backlight_timer_get_duty(void);
+
+// 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) {
+    backlight_pins_init();
+
+    backlight_set(get_backlight_level());
+
+#ifdef BACKLIGHT_BREATHING
+    if (is_backlight_breathing()) {
+        breathing_enable();
+    }
+#endif
+}
+
+void backlight_set(uint8_t level) {
+    if (level > BACKLIGHT_LEVELS) level = BACKLIGHT_LEVELS;
+
+    backlight_pins_off();
+
+    backlight_timer_set_duty(cie_lightness(0xFFFFU / BACKLIGHT_LEVELS * level));
+    backlight_timer_configure(level != 0);
+}
+
+static void backlight_timer_top(void) {
+#ifdef BACKLIGHT_BREATHING
+    if (is_breathing()) {
+        breathing_task();
+    }
+#endif
+
+    if (backlight_timer_get_duty() > 256) {
+        backlight_pins_on();
+    }
+}
+
+static void backlight_timer_cmp(void) { backlight_pins_off(); }
+
+void backlight_task(void) {}
+
+#ifdef BACKLIGHT_BREATHING
+#    define BREATHING_STEPS 128
+
+static bool     breathing         = false;
+static uint16_t breathing_counter = 0;
+
+/* 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(); }
+
+void breathing_task(void) {
+    uint8_t  breathing_period = get_breathing_period();
+    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;
+
+    // printf("index:%u\n", index);
+
+    backlight_timer_set_duty(cie_lightness(scale_backlight((uint16_t)breathing_table[index] * 256)));
+}
+
+bool is_breathing(void) { return breathing; }
+
+void breathing_enable(void) {
+    breathing_counter = 0;
+    breathing         = true;
+}
+void breathing_disable(void) { breathing = false; }
+
+void breathing_pulse(void) {
+    backlight_set(is_backlight_enabled() ? 0 : BACKLIGHT_LEVELS);
+    wait_ms(10);
+    backlight_set(is_backlight_enabled() ? get_backlight_level() : 0);
+}
+#endif
+
+#ifdef PROTOCOL_CHIBIOS
+// On Platforms where timers fire every tick and have no capture/top events
+//   - fake event in the normal timer callback
+uint16_t s_duty = 0;
+
+static void timerCallback(void) {
+    /* Software PWM
+     * timer:1111 1111 1111 1111
+     *       \______/| \_______/____  count(0-255)
+     *          \    \______________  unused(1)
+     *           \__________________  index of step table(0-127)
+     */
+
+    // this works for cca 65536 irqs/sec
+    static union {
+        uint16_t raw;
+        struct {
+            uint16_t count : 8;
+            uint8_t  dummy : 1;
+            uint8_t  index : 7;
+        } pwm;
+    } timer = {.raw = 0};
+
+    timer.raw++;
+
+    if (timer.pwm.count == 0) {
+        // LED on
+        backlight_timer_top();
+    } else if (timer.pwm.count == (s_duty / 256)) {
+        // LED off
+        backlight_timer_cmp();
+    }
+}
+
+static void     backlight_timer_set_duty(uint16_t duty) { s_duty = duty; }
+static uint16_t backlight_timer_get_duty(void) { return s_duty; }
+
+// ChibiOS - Map GPT timer onto Software PWM
+static void gptTimerCallback(GPTDriver *gptp) {
+    (void)gptp;
+    timerCallback();
+}
+
+static void backlight_timer_configure(bool enable) {
+    static const GPTConfig gptcfg = {1000000, gptTimerCallback, 0, 0};
+
+    static bool s_init = false;
+    if (!s_init) {
+        gptStart(&BACKLIGHT_GPT_DRIVER, &gptcfg);
+        s_init = true;
+    }
+
+    if (enable) {
+        gptStartContinuous(&BACKLIGHT_GPT_DRIVER, gptcfg.frequency / 0xFFFF);
+    } else {
+        gptStopTimer(&BACKLIGHT_GPT_DRIVER);
+    }
+}
+#endif