cleanup and test sinewave

include/filters.hpp

@@ -0,0 +1,7 @@
+#include <stdint.h>
+
+#include <function.hpp>
+
+auto simplest_lowpass(Function<uint32_t, int16_t> f_in) {
+    Function<uint32_t, int16_t> f_out;
+}

include/generators.hpp

@@ -0,0 +1,27 @@
+#include <math.h>
+#include <stdint.h>
+
+template<uint32_t period, int16_t max_val>
+int16_t sine(uint32_t t) {
+    // 0 <= t < period is 0 <= t_2pi < 2 pi
+    float t_2pi = 2 * M_PI / static_cast<float>(period) * t;
+    return static_cast<int16_t>(sinf(t_2pi)  * max_val);
+}
+
+template<uint32_t period, int16_t max_val>
+int16_t square(uint32_t t) {
+    if (t <= period / 2) {
+        return -max_val;
+    } else {
+        return max_val;
+    }
+}
+
+template<uint32_t period, int16_t max_val>
+int16_t sawtooth(uint32_t t) {
+    // f(t) = a t + y
+    // f(0) = -max_val = y
+    // f(period) = a * period - max_val = max_val
+    // a = 2 * max_val / period
+    return 2 * max_val * t / period - max_val;
+}

src/main.cpp

@@ -1,14 +1,48 @@
 #include <Arduino.h>
 
-constexpr unsigned SWITCH_DELAY_MS = 2000;
+#include "generators.hpp"
+#include "filters.hpp"
+
+constexpr int DAC_PIN = A2;
+
+constexpr uint16_t SAMPLING_RATE_HZ = 8000;
+
+constexpr unsigned long SAMPLE_US = 1000000 / SAMPLING_RATE_HZ;
+
+#ifndef LED_BUILTIN
+    #define LED_BUILTIN PC13
+#endif
+
+unsigned long last_time_us = 0;
+
+int16_t val;
+
+bool sample_computed = false;
+
+constexpr uint32_t hz_to_micros(uint32_t hz) {
+    return 1000000 / hz;
+}
 
 void setup() {
     delay(3000);
 }
 
 void loop() {
-    int val = analogRead(A0);
-    delay(20);
-    analogWrite(PA_4, val);
-    delay(20);
+    unsigned long time_us = micros();
+    unsigned long delta = time_us - last_time_us;
+    if (!sample_computed) {
+        if (delta < SAMPLE_US)  {
+            constexpr uint32_t period = hz_to_micros(412);
+            val = sine<period, 512>(time_us % period);
+            sample_computed = true;
+        }
+    }
+    else {
+        if (delta >= SAMPLE_US) {
+            last_time_us = time_us;
+            analogWrite(DAC_PIN, val);
+            sample_computed = false;
+        }
+    }
+    delayMicroseconds(1);
 }