From d915fd32a7becdf0f0492960fa5b241ee407aee9 Mon Sep 17 00:00:00 2001
From: Sarah Wilson <sarah@swilson.id.au>
Date: Fri, 10 Jan 2025 20:09:05 +1100
Subject: Initial version

---
 main.c | 182 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 182 insertions(+)
 create mode 100644 main.c

(limited to 'main.c')

diff --git a/main.c b/main.c
new file mode 100644
index 0000000..5c8bc76
--- /dev/null
+++ b/main.c
@@ -0,0 +1,182 @@
+#include <stdint.h>
+
+#include <avr/interrupt.h>
+#include <avr/io.h>
+#include <avr/sleep.h>
+
+#define max(a, b)                       \
+	({                              \
+		__typeof__(a) _a = (a); \
+		__typeof__(b) _b = (b); \
+		_a > _b ? _a : _b;      \
+	})
+
+#define min(a, b)                       \
+	({                              \
+		__typeof__(a) _a = (a); \
+		__typeof__(b) _b = (b); \
+		_a < _b ? _a : _b;      \
+	})
+
+// return a + (t/128)*(b-a)
+static uint8_t lerp(uint8_t a, uint8_t b, uint8_t t)
+{
+	return a + (uint8_t)(((int16_t)(b - a) * t) >> 7);
+}
+
+static void eeprom_write(uint16_t addr, uint8_t data)
+{
+	while (EECR & _BV(EEPE))
+		;
+	EEAR = addr;
+	EECR = 0;
+	EEDR = data;
+	EECR |= _BV(EEMPE);
+	EECR |= _BV(EEPE);
+}
+
+static uint8_t eeprom_read(uint16_t addr)
+{
+	while (EECR & _BV(EEPE))
+		;
+	EEAR = addr;
+	EECR = _BV(EERE);
+	return EEDR;
+}
+
+enum {
+	MODE_SOLID = 0,
+	MODE_PULSE,
+	MODE_ALTERNATE,
+	MODE_FAST_PULSE,
+	MODE_FAST_ALTERNATE,
+	MODE_VFAST_PULSE,
+	MODE_VFAST_ALTERNATE,
+	NUM_MODE,
+};
+
+uint16_t tickcount;
+static void tick(void);
+
+ISR(TIM0_COMPA_vect)
+{
+	++tickcount;
+	tick();
+}
+
+static uint8_t mode;
+ISR(PCINT0_vect)
+{
+	static uint16_t down;
+
+	if ((PINB & _BV(PB0)) == 0) {
+		down = tickcount;
+	} else {
+		if (tickcount - down > 100) {
+			eeprom_write(0, mode);
+		} else {
+			if (++mode == NUM_MODE) {
+				mode = MODE_SOLID;
+			}
+		}
+	}
+}
+
+static uint8_t brightness;
+ISR(ADC_vect)
+{
+	brightness = ADCH;
+}
+
+static uint8_t oa_duty, ob_duty;
+ISR(TIM1_OVF_vect)
+{
+	OCR1A = min(oa_duty, 127);
+	OCR1B = max(255 - ob_duty, 128);
+}
+
+void tick(void)
+{
+	ADCSRA |= _BV(ADSC);
+
+	switch (mode) {
+	case MODE_SOLID:
+		oa_duty = ob_duty = brightness >> 1;
+		break;
+	case MODE_PULSE:
+	case MODE_ALTERNATE:
+	case MODE_FAST_PULSE:
+	case MODE_FAST_ALTERNATE:
+	case MODE_VFAST_PULSE:
+	case MODE_VFAST_ALTERNATE: {
+		static uint8_t dir;
+		static uint8_t t;
+
+		oa_duty = lerp(0, brightness >> 1, dir ? t : 128 - t);
+		ob_duty = (mode & 1) ? oa_duty : ((brightness >> 1) - oa_duty);
+		t += mode > MODE_FAST_ALTERNATE ? 4 :
+		     mode > MODE_ALTERNATE	? 2 :
+						  1;
+		if (t >= 128) {
+			t = 0;
+			dir = !dir;
+		}
+	} break;
+	}
+}
+
+static void pwm_init(void)
+{
+	TCCR1 = _BV(PWM1A) | _BV(COM1A1);
+	GTCCR |= _BV(PWM1B) | _BV(COM1B1) | _BV(COM1B0);
+
+	TCCR1 |= _BV(CS12);
+
+	OCR1A = 0;
+	OCR1B = 255;
+
+	DDRB |= _BV(PB1) | _BV(PB4);
+
+	TIMSK |= _BV(TOIE1);
+}
+
+static void adc_init(void)
+{
+	ADMUX = _BV(ADLAR) | _BV(MUX0) | _BV(MUX1);
+	DIDR0 = _BV(ADC3D);
+	ADCSRA = _BV(ADEN) | _BV(ADIE) | _BV(ADPS2) | _BV(ADPS1);
+}
+
+static void tick_init(void)
+{
+	GTCCR = _BV(TSM) | _BV(PSR0);
+	TCCR0A = _BV(WGM01);
+	TCCR0B = _BV(CS01) | _BV(CS00);
+	OCR0A = 122; // 1M/64 = 15kHz / 122 = 128 hz tick
+	TIMSK |= _BV(OCIE0A);
+	GTCCR &= _BV(TSM);
+}
+
+int main(void)
+{
+	mode = eeprom_read(0);
+	if (mode >= NUM_MODE) {
+		mode = 0;
+	}
+
+	tick_init();
+	pwm_init();
+	adc_init();
+
+	DDRB &= ~_BV(PB0);
+	PORTB |= _BV(PB0);
+	GIMSK = _BV(PCIE);
+	PCMSK = _BV(PCINT0);
+
+	sei();
+
+	for (;;)
+		sleep_mode();
+
+	return (0);
+}
-- 
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