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#include <avr/io.h>
#include "backlight.h"
#define CHANNEL OCR1C
void backlight_init_ports()
{
// Setup PB7 as output and output low.
DDRB |= (1<<7);
PORTB &= ~(1<<7);
// Use full 16-bit resolution.
ICR1 = 0xFFFF;
// 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
// 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
TCCR1A = _BV(COM1C1) | _BV(WGM11); // = 0b00001010;
TCCR1B = _BV(WGM13) | _BV(WGM12) | _BV(CS10); // = 0b00011001;
backlight_init();
}
void backlight_set(uint8_t level)
{
if ( level == 0 )
{
// Turn off PWM control on PB7, revert to output low.
TCCR1A &= ~(_BV(COM1C1));
CHANNEL = 0x0;
// Prevent backlight blink on lowest level
PORTB &= ~(_BV(PORTB7));
}
else if ( level == BACKLIGHT_LEVELS )
{
// Prevent backlight blink on lowest level
PORTB &= ~(_BV(PORTB7));
// Turn on PWM control of PB7
TCCR1A |= _BV(COM1C1);
// Set the brightness
CHANNEL = 0xFFFF;
}
else
{
// Prevent backlight blink on lowest level
PORTB &= ~(_BV(PORTB7));
// Turn on PWM control of PB7
TCCR1A |= _BV(COM1C1);
// Set the brightness
CHANNEL = 0xFFFF >> ((BACKLIGHT_LEVELS - level) * ((BACKLIGHT_LEVELS + 1) / 2));
}
}
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