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-rw-r--r--keyboard/preonic/backlight.c61
1 files changed, 61 insertions, 0 deletions
diff --git a/keyboard/preonic/backlight.c b/keyboard/preonic/backlight.c
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+++ b/keyboard/preonic/backlight.c
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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));
+ }
+} \ No newline at end of file