61 lines
1.7 KiB
C
61 lines
1.7 KiB
C
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#include <avr/io.h>
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#include "backlight.h"
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#define CHANNEL OCR1C
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void backlight_init_ports()
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{
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// Setup PB7 as output and output low.
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DDRB |= (1<<7);
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PORTB &= ~(1<<7);
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// Use full 16-bit resolution.
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ICR1 = 0xFFFF;
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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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// Pin PB7 = OCR1C (Timer 1, Channel C)
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// Compare Output Mode = Clear on compare match, Channel C = COM1C1=1 COM1C0=0
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// (i.e. start high, go low when counter matches.)
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// WGM Mode 14 (Fast PWM) = WGM13=1 WGM12=1 WGM11=1 WGM10=0
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// Clock Select = clk/1 (no prescaling) = CS12=0 CS11=0 CS10=1
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TCCR1A = _BV(COM1C1) | _BV(WGM11); // = 0b00001010;
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TCCR1B = _BV(WGM13) | _BV(WGM12) | _BV(CS10); // = 0b00011001;
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backlight_init();
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}
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void backlight_set(uint8_t level)
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{
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if ( level == 0 )
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{
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// Turn off PWM control on PB7, revert to output low.
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TCCR1A &= ~(_BV(COM1C1));
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CHANNEL = 0x0;
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// Prevent backlight blink on lowest level
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PORTB &= ~(_BV(PORTB7));
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}
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else if ( level == BACKLIGHT_LEVELS )
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{
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// Prevent backlight blink on lowest level
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PORTB &= ~(_BV(PORTB7));
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// Turn on PWM control of PB7
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TCCR1A |= _BV(COM1C1);
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// Set the brightness
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CHANNEL = 0xFFFF;
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}
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else
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{
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// Prevent backlight blink on lowest level
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PORTB &= ~(_BV(PORTB7));
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// Turn on PWM control of PB7
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TCCR1A |= _BV(COM1C1);
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// Set the brightness
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CHANNEL = 0xFFFF >> ((BACKLIGHT_LEVELS - level) * ((BACKLIGHT_LEVELS + 1) / 2));
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}
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}
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