keyboard/planck/backlight.c

   1
   2 #include <avr/io.h>
   3 #include "backlight.h"
   4
   5
   6 void backlight_init_ports()
   7 {
   8         // Setup PB7 as output and output low.
   9         DDRB |= (1<<7);
  10         PORTB &= ~(1<<7);
  11
  12         // Use full 16-bit resolution.
  13         ICR1 = 0xFFFF;
  14
  15         // I could write a wall of text here to explain... but TL;DW
  16         // Go read the ATmega32u4 datasheet.
  17         // And this: http://blog.saikoled.com/post/43165849837/secret-konami-cheat-code-to-high-resolution-pwm-on
  18
  19         // Pin PB7 = OCR1C (Timer 1, Channel C)
  20         // Compare Output Mode = Clear on compare match, Channel C = COM1C1=1 COM1C0=0
  21         // (i.e. start high, go low when counter matches.)
  22         // WGM Mode 14 (Fast PWM) = WGM13=1 WGM12=1 WGM11=1 WGM10=0
  23         // Clock Select = clk/1 (no prescaling) = CS12=0 CS11=0 CS10=1
  24
  25         TCCR1A = _BV(COM1C1) | _BV(WGM11); // = 0b00001010;
  26         TCCR1B = _BV(WGM13) | _BV(WGM12) | _BV(CS10); // = 0b00011001;
  27
  28         // Default to zero duty cycle.
  29         OCR1C = 0x0000;
  30 }
  31
  32 void backlight_set(uint8_t level)
  33 {
  34         if ( level == 0 )
  35         {
  36                 // Turn off PWM control on PB7, revert to output low.
  37                 TCCR1A &= ~(_BV(COM1C1));
  38         }
  39         else
  40         {
  41                 // Turn on PWM control of PB7
  42                 TCCR1A |= _BV(COM1C1);
  43                 OCR1C = level << 12 | 0x0FFF;
  44         }
  45 }
  46