1 files changed, 62 insertions, 1 deletions
diff --git a/keyboard/preonic/preonic.c b/keyboard/preonic/preonic.c
index f639f247a5..211f8d0296 100644
--- a/keyboard/preonic/preonic.c
+++ b/keyboard/preonic/preonic.c
@@ -38,4 +38,65 @@ void matrix_scan_kb(void) {
 
 void process_action_kb(keyrecord_t *record) {
 	process_action_user(record);
-}
-\ No newline at end of file
+}
+
+#ifdef BACKLIGHT_ENABLE
+#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));
+    }
+}
+
+#endif
+\ No newline at end of file