backlight: split AVR PWM and timer drivers (#21540)
Ryan
2 years ago
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b090354143
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4137685f8e
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#include "backlight.h" |
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#include "backlight_driver_common.h" |
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#include "progmem.h" |
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#include <avr/io.h> |
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#include <avr/interrupt.h> |
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// Maximum duty cycle limit
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#ifndef BACKLIGHT_LIMIT_VAL |
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# define BACKLIGHT_LIMIT_VAL 255 |
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#endif |
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#ifndef BACKLIGHT_PWM_TIMER |
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# define BACKLIGHT_PWM_TIMER 1 |
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#endif |
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#if BACKLIGHT_PWM_TIMER == 1 |
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# define ICRx ICR1 |
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# define TCCRxA TCCR1A |
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# define TCCRxB TCCR1B |
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# define TIMERx_COMPA_vect TIMER1_COMPA_vect |
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# define TIMERx_OVF_vect TIMER1_OVF_vect |
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# if defined(__AVR_ATmega32A__) // This MCU has only one TIMSK register
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# define TIMSKx TIMSK |
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# else |
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# define TIMSKx TIMSK1 |
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# endif |
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# define TOIEx TOIE1 |
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# define OCIExA OCIE1A |
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# define OCRxx OCR1A |
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#elif BACKLIGHT_PWM_TIMER == 3 |
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# define ICRx ICR1 |
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# define TCCRxA TCCR3A |
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# define TCCRxB TCCR3B |
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# define TIMERx_COMPA_vect TIMER3_COMPA_vect |
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# define TIMERx_OVF_vect TIMER3_OVF_vect |
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# define TIMSKx TIMSK3 |
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# define TOIEx TOIE3 |
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# define OCIExA OCIE3A |
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# define OCRxx OCR3A |
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#else |
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# error Invalid backlight PWM timer! |
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#endif |
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#ifndef BACKLIGHT_RESOLUTION |
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# define BACKLIGHT_RESOLUTION 0xFFFFU |
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#endif |
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#if (BACKLIGHT_RESOLUTION > 0xFFFF || BACKLIGHT_RESOLUTION < 0x00FF) |
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# error "Backlight resolution must be between 0x00FF and 0xFFFF" |
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#endif |
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#define BREATHING_SCALE_FACTOR F_CPU / BACKLIGHT_RESOLUTION / 120 |
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// The idea of software PWM assisted by hardware timers is the following
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// we use the hardware timer in fast PWM mode like for hardware PWM, but
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// instead of letting the Output Match Comparator control the led pin
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// (which is not possible since the backlight is not wired to PWM pins on the
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// CPU), we do the LED on/off by oursleves.
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// The timer is setup to count up to 0xFFFF, and we set the Output Compare
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// register to the current 16bits backlight level (after CIE correction).
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// This means the CPU will trigger a compare match interrupt when the counter
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// reaches the backlight level, where we turn off the LEDs,
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// but also an overflow interrupt when the counter rolls back to 0,
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// in which we're going to turn on the LEDs.
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// The LED will then be on for OCRxx/0xFFFF time, adjusted every 244Hz,
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// or F_CPU/BACKLIGHT_RESOLUTION if used.
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// Triggered when the counter reaches the OCRx value
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ISR(TIMERx_COMPA_vect) { |
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backlight_pins_off(); |
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} |
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// Triggered when the counter reaches the TOP value
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// this one triggers at F_CPU/ICRx = 16MHz/65536 =~ 244 Hz
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ISR(TIMERx_OVF_vect) { |
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#ifdef BACKLIGHT_BREATHING |
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if (is_breathing()) { |
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breathing_task(); |
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} |
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#endif |
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// for very small values of OCRxx (or backlight level)
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// we can't guarantee this whole code won't execute
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// at the same time as the compare match interrupt
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// which means that we might turn on the leds while
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// trying to turn them off, leading to flickering
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// artifacts (especially while breathing, because breathing_task
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// takes many computation cycles).
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// so better not turn them on while the counter TOP is very low.
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if (OCRxx > ICRx / 250 + 5) { |
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backlight_pins_on(); |
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} |
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} |
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// See http://jared.geek.nz/2013/feb/linear-led-pwm
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static uint16_t cie_lightness(uint16_t v) { |
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if (v <= (uint32_t)ICRx / 12) // If the value is less than or equal to ~8% of max
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{ |
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return v / 9; // Same as dividing by 900%
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} else { |
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// In the next two lines values are bit-shifted. This is to avoid loosing decimals in integer math.
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uint32_t y = (((uint32_t)v + (uint32_t)ICRx / 6) << 5) / ((uint32_t)ICRx / 6 + ICRx); // If above 8%, add ~16% of max, and normalize with (max + ~16% max)
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uint32_t out = (y * y * y * ICRx) >> 15; // Cube it and undo the bit-shifting. (which is now three times as much due to the cubing)
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if (out > ICRx) // Avoid overflows
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{ |
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out = ICRx; |
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} |
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return (uint16_t)out; |
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} |
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} |
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// rescale the supplied backlight value to be in terms of the value limit // range for val is [0..ICRx]. PWM pin is high while the timer count is below val.
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static uint32_t rescale_limit_val(uint32_t val) { |
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return (val * (BACKLIGHT_LIMIT_VAL + 1)) / 256; |
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} |
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// range for val is [0..ICRx]. PWM pin is high while the timer count is below val.
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static inline void set_pwm(uint16_t val) { |
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OCRxx = val; |
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} |
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void backlight_set(uint8_t level) { |
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if (level > BACKLIGHT_LEVELS) level = BACKLIGHT_LEVELS; |
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if (level == 0) { |
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if (OCRxx) { |
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TIMSKx &= ~(_BV(OCIExA)); |
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TIMSKx &= ~(_BV(TOIEx)); |
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} |
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backlight_pins_off(); |
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} else { |
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if (!OCRxx) { |
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TIMSKx |= _BV(OCIExA); |
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TIMSKx |= _BV(TOIEx); |
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} |
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} |
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// Set the brightness
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set_pwm(cie_lightness(rescale_limit_val(ICRx * (uint32_t)level / BACKLIGHT_LEVELS))); |
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} |
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void backlight_task(void) {} |
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#ifdef BACKLIGHT_BREATHING |
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# define BREATHING_NO_HALT 0 |
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# define BREATHING_HALT_OFF 1 |
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# define BREATHING_HALT_ON 2 |
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# define BREATHING_STEPS 128 |
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static uint8_t breathing_halt = BREATHING_NO_HALT; |
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static uint16_t breathing_counter = 0; |
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static uint8_t breath_scale_counter = 1; |
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/* Run the breathing loop at ~120Hz*/ |
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const uint8_t breathing_ISR_frequency = 120; |
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static bool breathing = false; |
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bool is_breathing(void) { |
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return breathing; |
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} |
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# define breathing_interrupt_enable() \ |
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do { \
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breathing = true; \
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} while (0) |
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# define breathing_interrupt_disable() \ |
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do { \
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breathing = false; \
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} while (0) |
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# define breathing_min() \ |
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do { \
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breathing_counter = 0; \
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} while (0) |
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# define breathing_max() \ |
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do { \
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breathing_counter = get_breathing_period() * breathing_ISR_frequency / 2; \
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} while (0) |
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void breathing_enable(void) { |
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breathing_counter = 0; |
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breathing_halt = BREATHING_NO_HALT; |
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breathing_interrupt_enable(); |
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} |
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void breathing_pulse(void) { |
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if (get_backlight_level() == 0) |
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breathing_min(); |
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else |
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breathing_max(); |
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breathing_halt = BREATHING_HALT_ON; |
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breathing_interrupt_enable(); |
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} |
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void breathing_disable(void) { |
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breathing_interrupt_disable(); |
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// Restore backlight level
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backlight_set(get_backlight_level()); |
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} |
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void breathing_self_disable(void) { |
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if (get_backlight_level() == 0) |
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breathing_halt = BREATHING_HALT_OFF; |
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else |
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breathing_halt = BREATHING_HALT_ON; |
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} |
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/* To generate breathing curve in python:
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* from math import sin, pi; [int(sin(x/128.0*pi)**4*255) for x in range(128)] |
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*/ |
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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}; |
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// Use this before the cie_lightness function.
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static inline uint16_t scale_backlight(uint16_t v) { |
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return v / BACKLIGHT_LEVELS * get_backlight_level(); |
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} |
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void breathing_task(void) { |
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// Only run this ISR at ~120 Hz
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if (breath_scale_counter++ == BREATHING_SCALE_FACTOR) { |
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breath_scale_counter = 1; |
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} else { |
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return; |
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} |
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uint16_t interval = (uint16_t)get_breathing_period() * breathing_ISR_frequency / BREATHING_STEPS; |
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// resetting after one period to prevent ugly reset at overflow.
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breathing_counter = (breathing_counter + 1) % (get_breathing_period() * breathing_ISR_frequency); |
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uint8_t index = breathing_counter / interval; |
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// limit index to max step value
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if (index >= BREATHING_STEPS) { |
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index = BREATHING_STEPS - 1; |
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} |
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if (((breathing_halt == BREATHING_HALT_ON) && (index == BREATHING_STEPS / 2)) || ((breathing_halt == BREATHING_HALT_OFF) && (index == BREATHING_STEPS - 1))) { |
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breathing_interrupt_disable(); |
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} |
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// Set PWM to a brightnessvalue scaled to the configured resolution
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set_pwm(cie_lightness(rescale_limit_val(scale_backlight((uint32_t)pgm_read_byte(&breathing_table[index]) * ICRx / 255)))); |
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} |
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#endif // BACKLIGHT_BREATHING
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void backlight_init_ports(void) { |
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// Setup backlight pin as output and output to on state.
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backlight_pins_init(); |
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// I could write a wall of text here to explain... but TL;DW
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// Go read the ATmega32u4 datasheet.
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// And this: http://blog.saikoled.com/post/43165849837/secret-konami-cheat-code-to-high-resolution-pwm-on
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// TimerX setup, Fast PWM mode count to TOP set in ICRx
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TCCRxA = _BV(WGM11); // = 0b00000010;
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// clock select clk/1
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TCCRxB = _BV(WGM13) | _BV(WGM12) | _BV(CS10); // = 0b00011001;
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ICRx = BACKLIGHT_RESOLUTION; |
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backlight_init(); |
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#ifdef BACKLIGHT_BREATHING |
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if (is_backlight_breathing()) { |
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breathing_enable(); |
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} |
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#endif |
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} |
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