include/filters.hpp

@@ -1,7 +1,7 @@
 #include <stdint.h>
 
-typedef int32_t (*FUN)(int32_t);
+#include <function.hpp>
 
-int32_t stretch(FUN f, float multiplicator, int32_t value) {
+auto simplest_lowpass(Function<uint32_t, int16_t> f_in) {
-    return f(multiplicator * value);
+    Function<uint32_t, int16_t> f_out;
 }

include/generators.hpp

@@ -1,17 +1,15 @@
 #include <math.h>
 #include <stdint.h>
 
-template<int32_t period, int32_t max_val>
+template<uint32_t period, int16_t max_val>
-int32_t sine(int32_t t) {
+int16_t sine(uint32_t t) {
     // 0 <= t < period is 0 <= t_2pi < 2 pi
-    t %= period;
+    float t_2pi = 2 * M_PI / static_cast<float>(period) * t;
-    float t_2pi =  2 * M_PI / static_cast<float>(period) * t;
+    return static_cast<int16_t>(sinf(t_2pi)  * max_val);
-    return static_cast<int32_t>(sinf(t_2pi) * max_val);
 }
 
-template<int32_t period, int32_t max_val>
+template<uint32_t period, int16_t max_val>
-int32_t square(int32_t t) {
+int16_t square(uint32_t t) {
-    t %= period;
     if (t <= period / 2) {
         return -max_val;
     } else {
@@ -19,12 +17,11 @@ int32_t square(int32_t t) {
     }
 }
 
-template<int32_t period, int32_t max_val>
+template<uint32_t period, int16_t max_val>
-int32_t sawtooth(int32_t t) {
+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
-    t %= period;
     return 2 * max_val * t / period - max_val;
 }

src/main.cpp

@@ -5,67 +5,44 @@
 
 constexpr int DAC_PIN = A2;
 
-constexpr uint32_t SAMPLING_RATE_HZ = 44100;
+constexpr uint16_t SAMPLING_RATE_HZ = 8000;
 
-constexpr uint32_t SAMPLE_US = 1000000 / SAMPLING_RATE_HZ;
+constexpr unsigned long SAMPLE_US = 1000000 / SAMPLING_RATE_HZ;
+
+#ifndef LED_BUILTIN
+    #define LED_BUILTIN PC13
+#endif
 
 unsigned long last_time_us = 0;
 
-int32_t sample, next_sample;
+int16_t val;
-int32_t i = 0;
-int32_t sample_count = 0;
 
-bool next_sample_computed = false;
+bool sample_computed = false;
 
 constexpr uint32_t hz_to_micros(uint32_t hz) {
     return 1000000 / hz;
 }
 
-constexpr uint32_t mhz_to_micros(uint32_t mhz) {
-    return 1000 * hz_to_micros(mhz);
-}
-
-template<int32_t min, int32_t max>
-constexpr int32_t shift_and_restrict(int32_t val) {
-    val += (max - min) / 2 + 1;
-    if (val < min) {
-        val = min;
-    }
-    if (val > max) {
-        val = max;
-    }
-    return val;
-}
-
-void writeVal(int32_t val) {
-    val = shift_and_restrict<0, 255>(val);
-    analogWrite(DAC_PIN, val);
-}
-
 void setup() {
-    delay(1000);
+    delay(3000);
 }
 
 void loop() {
-    static int32_t note = -56;
     unsigned long time_us = micros();
-    uint32_t delta = time_us - last_time_us;
+    unsigned long delta = time_us - last_time_us;
-    if (!next_sample_computed) {
+    if (!sample_computed) {
-            constexpr uint32_t period = hz_to_micros(440);
+        if (delta < SAMPLE_US)  {
-            next_sample = stretch(sine<period, 127>, powf(2, note / 12.0), time_us);
+            constexpr uint32_t period = hz_to_micros(412);
-            next_sample_computed = true;
+            val = sine<period, 512>(time_us % period);
-    }
+            sample_computed = true;
-    if (delta >= SAMPLE_US) {
-        last_time_us = time_us;
-        writeVal(next_sample);
-        next_sample_computed = false;
-        ++sample_count;
-    }
-    if (16 * sample_count >= SAMPLING_RATE_HZ) {
-        sample_count = 0;
-        ++note;
-        if (note > 12) {
-            note = -56;
         }
     }
+    else {
+        if (delta >= SAMPLE_US) {
+            last_time_us = time_us;
+            analogWrite(DAC_PIN, val);
+            sample_computed = false;
+        }
+    }
+    delayMicroseconds(1);
 }