From d8092ae891d96da4bf6daac37a6588150e6a724e Mon Sep 17 00:00:00 2001
From: Lars-Dominik Braun <lars@6xq.net>
Date: Tue, 27 May 2014 15:02:33 +0200
Subject: pwm: Initial LED PWM

---
 pwm.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 pwm.c

(limited to 'pwm.c')

diff --git a/pwm.c b/pwm.c
new file mode 100644
index 0000000..eaaa5af
--- /dev/null
+++ b/pwm.c
@@ -0,0 +1,81 @@
+/*	LED pwm, uses timer0
+ *	XXX: this works, but we should use non-linear steps
+ */
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <stdbool.h>
+
+#include "speaker.h"
+
+#define PWM_STEPS 16
+
+/* inverse brightness; 0 is max brightness, PWM_STEPS off */
+static uint8_t invbrightness[6];
+static uint8_t count = 0;
+
+ISR(TIMER0_COMPA_vect) {
+	if (count == 0) {
+		/* switch off all LEDs */
+		PORTB = PORTB & ~((1 << PB6) | (1 << PB7));
+		PORTD = PORTD & ~((1 << PD2) | (1 << PD3) | (1 << PD4) | (1 << PD5));
+	} else {
+		uint8_t pb = 0, pd = 0;
+		if (count > invbrightness[0]) {
+			pb |= (1 << PB6);
+		}
+		if (count > invbrightness[1]) {
+			pb |= (1 << PB7);
+		}
+		if (count > invbrightness[2]) {
+			pd |= (1 << PD2);
+		}
+		if (count > invbrightness[3]) {
+			pd |= (1 << PD3);
+		}
+		if (count > invbrightness[4]) {
+			pd |= (1 << PD4);
+		}
+		if (count > invbrightness[5]) {
+			pd |= (1 << PD5);
+		}
+		/* actually set them */
+		PORTB |= pb;
+		PORTD |= pd;
+	}
+	++count;
+	if (count >= PWM_STEPS) {
+		count = 0;
+	}
+}
+
+void pwmInit () {
+	/* set led1,led2 to output */
+	DDRB |= (1 << PB6) | (1 << PB7);
+	/* set led3,led4,led5,led6 to output */
+	DDRD |= (1 << PD2) | (1 << PD3) | (1 << PD4) | (1 << PD5);
+}
+
+void pwmStart () {
+	/* reset timer value */
+	TCNT0 = 0;
+	/* set ctc timer0 (part 1) */
+	TCCR0A = 0;
+	/* enable compare match interrupt */
+	TIMSK0 = (1 << OCIE0A);
+	/* compare value; interrupt on every tick */
+	OCR0A = 0;
+	/* io clock with 8 prescaler (>8 is too slow and starts flickering); ctc
+	 * (part 2) */
+	TCCR0B = (1 << CS01) | (1 << WGM02);
+}
+
+void pwmStop () {
+	/* zero clock source */
+	TCCR0B = 0;
+}
+
+void pwmSetBrightness (const uint8_t i, const uint8_t b) {
+	invbrightness[i] = b;
+}
+
-- 
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