qmk_firmware/quantum/backlight/backlight_avr.c

#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(pin_t backlight_pin) {
#    if BACKLIGHT_ON_STATE == 0
    writePinLow(backlight_pin);
#    else
    writePinHigh(backlight_pin);
#    endif
}

void backlight_off(pin_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++) { \
                pin_t backlight_pin = backlight_pins[i];        \
                { x }                                           \
            }

static const pin_t backlight_pins[BACKLIGHT_LED_COUNT] = BACKLIGHT_PIN_INIT;

#    else  // full hardware PWM

// we support only one backlight pin
static const pin_t backlight_pin = BACKLIGHT_PIN;
#        define FOR_EACH_LED(x) x

#    endif

#    ifdef NO_HARDWARE_PWM
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
}

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
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_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 = get_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();
}

/* 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
{
    uint8_t breathing_period = get_breathing_period();
    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

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

#endif  // backlight