#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)); } }