true

.gitignore

@@ -0,0 +1 @@
+build/

.vscode/c_cpp_properties.json

@@ -0,0 +1,28 @@
+{
+    "configurations": [
+        {
+            "name": "AVR",
+            "intelliSenseMode": "${default}",
+            "cStandard": "${default}",
+            "cppStandard": "${default}",
+            "includePath": [
+                "/usr/avr/lib/**",
+                "/usr/avr/include/**"
+            ],
+            "compilerArgs": [
+                "-g",
+                "-Os",
+                "-Wall",
+                "-Wextra",
+                "-fpermissive",
+                "-fno-exceptions",
+                "-fno-threadsafe-statics",
+                "-pipe",
+                "-mmcu=atmega2560",
+                "-DF_CPU=16000000UL"
+            ],
+            "compilerPath": "/usr/bin/avr-gcc"
+        }
+    ],
+    "version": 4
+}

.vscode/extensions.json

@@ -0,0 +1,6 @@
+{
+    "recommendations": [
+        "alex079.vscode-avr-helper",
+        "ms-vscode.cpptools"
+    ]
+}

.vscode/settings.json

@@ -0,0 +1,20 @@
+{
+    "AVR.reporter.arguments": [
+        "-C"
+    ],
+    "AVR.source.compiler": "/usr/bin/avr-gcc",
+    "AVR.programmer.tool": "/usr/bin/avrdude",
+    "AVR.source.libraries": [
+        "/usr/avr/lib",
+        "/usr/avr/include"
+    ],
+    "C_Cpp.default.compilerPath": "/usr/bin/avr-gcc",
+    "AVR.device.type": "atmega2560",
+    "AVR.device.frequency": 16000000,
+    "AVR.programmer.type": "wiring",
+    "AVR.programmer.port": "/dev/ttyACM1",
+    "AVR.programmer.rate": 115200,
+    "AVR.programmer.arguments": [
+        "-D"
+    ]
+}

main.c

@@ -0,0 +1,80 @@
+#define __AVR_ATmega2560__
+#define F_CPU 16000000UL
+
+#include <avr/io.h>
+#include <util/delay.h>
+#include <stdbool.h>
+#include <avr/interrupt.h>
+
+uint16_t freq_high = 1200;
+uint16_t freq_low = 800;
+volatile uint8_t speed = 25;
+volatile uint8_t tick_count = 0;
+volatile uint16_t beep_time = 0;
+volatile int debounce_int2 = 10;
+volatile int debounce_int3 = 10;
+volatile int tick_timer_start =  0xffff;
+
+void start_timer() {
+    TCCR1B |= _BV(CS10) | _BV(CS12); // clk/1024
+    TIMSK1 |= _BV(TOIE1);
+
+    TCCR4B |= _BV(CS41); // clk/8
+    TIMSK4 |= _BV(OCIE4A);
+    TCNT1 = tick_timer_start;
+
+    // Enable interrupts
+    sei();
+}
+
+ISR(INT2_vect) {
+    if (debounce_int2) return;
+    debounce_int2 = 100;
+
+    if (speed < 100) speed++;
+}
+
+ISR(INT3_vect) {
+    if (debounce_int3) return;
+    debounce_int3 = 100;
+
+    if (speed > 1) speed--;
+}
+
+ISR(TIMER1_OVF_vect) {
+    tick_count++;
+    if (tick_count > 3) tick_count = 0;
+
+    beep_time = 50;
+
+    TCNT1 = tick_timer_start;
+}
+
+ISR(TIMER4_COMPA_vect) {
+    if (beep_time > 0) {
+        PORTK ^= 0b10000000;
+        beep_time--;
+    }
+    TCNT4 = 0;
+}
+
+void main() {
+    DDRK = 0b10000000;
+    DDRD = 0b00000000;
+    PORTD |= 0b00001100;
+
+    // EIMSK controls which ports can trigger interrupts
+    EIMSK |= _BV(INT2) | _BV(INT3);
+    // Trigger on falling edge on INT2 and INT3
+    EICRA |= _BV(ISC21) | _BV(ISC31);
+
+    start_timer();
+    while (true) {
+        OCR4A = (F_CPU / 8) / (tick_count == 0 ? freq_high : freq_low);
+        tick_timer_start =  0xffff - (F_CPU / 1024 / 1000) * (100 + speed * 10);
+
+        if (debounce_int2 > 0) debounce_int2--;
+        if (debounce_int3 > 0) debounce_int3--;
+        _delay_ms(1);
+    }
+}