qmk_firmware/platforms/chibios/drivers/backlight_pwm.c

#include "backlight.h"
#include "gpio.h"
#include "wait.h"
#include <hal.h>

// Maximum duty cycle limit
#ifndef BACKLIGHT_LIMIT_VAL
#    define BACKLIGHT_LIMIT_VAL 255
#endif

#ifndef BACKLIGHT_PAL_MODE
#    if defined(USE_GPIOV1)
#        define BACKLIGHT_PAL_MODE PAL_MODE_ALTERNATE_PUSHPULL
#    else
// GPIOV2 && GPIOV3
#        define BACKLIGHT_PAL_MODE 2
#    endif
#endif

// GENERIC
#ifndef BACKLIGHT_PWM_DRIVER
#    define BACKLIGHT_PWM_DRIVER PWMD4
#endif
#ifndef BACKLIGHT_PWM_CHANNEL
#    define BACKLIGHT_PWM_CHANNEL 3
#endif

// Support for pins which are on TIM1_CH1N - requires STM32_PWM_USE_ADVANCED
#ifdef BACKLIGHT_PWM_COMPLEMENTARY_OUTPUT
#    if BACKLIGHT_ON_STATE == 1
#        define PWM_OUTPUT_MODE PWM_COMPLEMENTARY_OUTPUT_ACTIVE_LOW;
#    else
#        define PWM_OUTPUT_MODE PWM_COMPLEMENTARY_OUTPUT_ACTIVE_HIGH;
#    endif
#else
#    if BACKLIGHT_ON_STATE == 1
#        define PWM_OUTPUT_MODE PWM_OUTPUT_ACTIVE_HIGH;
#    else
#        define PWM_OUTPUT_MODE PWM_OUTPUT_ACTIVE_LOW;
#    endif
#endif

#ifndef BACKLIGHT_PWM_COUNTER_FREQUENCY
#    define BACKLIGHT_PWM_COUNTER_FREQUENCY 0xFFFF
#endif

#ifndef BACKLIGHT_PWM_PERIOD
#    define BACKLIGHT_PWM_PERIOD 256
#endif

static PWMConfig pwmCFG = {
    .frequency = BACKLIGHT_PWM_COUNTER_FREQUENCY, /* PWM clock frequency  */
    .period    = BACKLIGHT_PWM_PERIOD,            /* PWM period in counter ticks. e.g. clock frequency is 10KHz, period is 256 ticks then t_period is 25.6ms */
};

#ifdef BACKLIGHT_BREATHING
static virtual_timer_t breathing_vt;
#endif

// 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;
        }
    }
}

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), BACKLIGHT_PAL_MODE);
#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_MODE;
    pwmStart(&BACKLIGHT_PWM_DRIVER, &pwmCFG);

    backlight_set(get_backlight_level());

#ifdef BACKLIGHT_BREATHING
    chVTObjectInit(&breathing_vt);
    if (is_backlight_breathing()) {
        breathing_enable();
    }
#endif
}

void backlight_set(uint8_t level) {
    if (level > BACKLIGHT_LEVELS) {
        level = BACKLIGHT_LEVELS;
    }

    if (level == 0) {
        // Turn backlight off
        pwmDisableChannel(&BACKLIGHT_PWM_DRIVER, BACKLIGHT_PWM_CHANNEL - 1);
    } else {
        // Turn backlight on
        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));
    }
}

void backlight_task(void) {}

#ifdef BACKLIGHT_BREATHING

#    define BREATHING_STEPS 128

/* 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};

static void breathing_callback(virtual_timer_t *vtp, void *p);

bool is_breathing(void) {
    return chVTIsArmed(&breathing_vt);
}

void breathing_enable(void) {
    /* Update frequency is 256Hz -> 3906us intervals */
    chVTSetContinuous(&breathing_vt, TIME_US2I(3906), breathing_callback, NULL);
}

void breathing_disable(void) {
    chVTReset(&breathing_vt);

    // Restore backlight level
    backlight_set(get_backlight_level());
}

// 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(virtual_timer_t *vtp, void *p) {
    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.
    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(rescale_limit_val(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();
}

// TODO: integrate generic pulse solution
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