examples/Waveform_Generator.ino: Update example.

* Add new command to stop DAC ("k").
* Print memory usage.
* Increase max frequency to 128KHz.
* Use a smaller DMA buffer size and rework the wave generators
to support it.

Author: iabdalkader

examples/Beginner/Waveform_Generator/Waveform_Generator.ino

@@ -1,30 +1,51 @@
 // This example generates different waveforms based on user input on A12/DAC1.
 
 #include <Arduino_AdvancedAnalog.h>
+#include <mbed_stats.h>
 
-#define N_SAMPLES           (256)
-#define DEFAULT_FREQUENCY   (16000)
+#define N_SAMPLES           (64)
+#define DEFAULT_FREQUENCY   (32000)
 
 AdvancedDAC dac1(A12);
 uint8_t SAMPLES_BUFFER[N_SAMPLES];
-size_t dac_frequency = DEFAULT_FREQUENCY;
 
-void generate_waveform(int cmd) 
-{   
+uint32_t get_current_heap() {
+    mbed_stats_heap_t heap_stats;
+    mbed_stats_heap_get(&heap_stats);
+    return heap_stats.current_size;
+}
+
+void print_menu() {
+    Serial.println();
+    Serial.println("Enter a command:");
+    Serial.println("t: Triangle wave");
+    Serial.println("q: Square wave");
+    Serial.println("s: Sine wave");
+    Serial.println("r: Sawtooth wave");
+    Serial.println("k: stop DAC");
+    Serial.println("+: Increase frequency");
+    Serial.println("-: Decrease frequency");
+}
+
+void generate_waveform(int cmd) {
+    static bool dac_started = false;
+    static size_t dac_frequency = DEFAULT_FREQUENCY;
+    static size_t starting_heap = get_current_heap();
+
     switch (cmd) {
         case 't':
             // Triangle wave
             Serial.print("Waveform: Triangle ");
-            for (int i=0; i<N_SAMPLES; i++){
-                SAMPLES_BUFFER[i] = abs((i % 255) - 127);
+            for (int i=0, j=N_SAMPLES-1; i<N_SAMPLES; i++, j--){
+                SAMPLES_BUFFER[i] = abs((i - j) * 256 / N_SAMPLES);
             }
             break;
 
         case 'q':
             // Square wave
             Serial.print("Waveform: Square ");
             for (int i=0; i<N_SAMPLES; i++){
-                SAMPLES_BUFFER[i] = (i % 255) < 127 ? 127 : 0;
+                SAMPLES_BUFFER[i] = i < (N_SAMPLES / 2) ? 0 : 255;
             }
             break;
 
@@ -38,36 +59,59 @@ void generate_waveform(int cmd)
 
         case 'r':
             // Sawtooth
-            Serial.print("Waveform: Sawtooth");
+            Serial.print("Waveform: Sawtooth ");
             for (int i=0; i<N_SAMPLES; i++){
-                SAMPLES_BUFFER[i] = i;
+                SAMPLES_BUFFER[i] = i * (256 / N_SAMPLES);
             }
             break;
 
         case '+':
         case '-':
             Serial.print("Current frequency: ");
-            
-            if (cmd == '+' && dac_frequency < 64000) {
-              dac_frequency *= 2;
+
+            if (cmd == '+' && dac_frequency < 128000) {
+                dac_frequency *= 2;
             } else if (cmd == '-' && dac_frequency > 1000) {
-              dac_frequency /= 2;
+                dac_frequency /= 2;
             } else {
-              break;
+                break;
             }
 
             // Change frequency.
             dac1.frequency(dac_frequency * N_SAMPLES);
             break;
-            
+
+        case 'k':
+            dac1.stop();
+            dac_started = false;
+            break;
+
         default:
             Serial.print("Unknown command ");
             Serial.println((char) cmd);
             return;
     }
-    
-    Serial.print(dac_frequency/1000);
-    Serial.println("KHz");
+
+    if (cmd == 'k') {
+        Serial.println("DAC stopped!");
+        print_menu();
+    } else {
+        Serial.print(dac_frequency/1000);
+        Serial.println("KHz");
+
+        if (dac_started == false) {
+            // Initialize and start the DAC.
+            if (!dac1.begin(AN_RESOLUTION_8, dac_frequency * N_SAMPLES, N_SAMPLES, 32)) {
+                Serial.println("Failed to start DAC1 !");
+                while (1);
+            }
+            dac_started = true;
+        }
+    }
+
+    Serial.print("Used memory: ");
+    Serial.print(get_current_heap() - starting_heap);
+    Serial.println(" bytes");
 }
 
 void setup() {
@@ -77,32 +121,21 @@ void setup() {
 
     }
 
-    
-    Serial.println("Enter a command:");
-    Serial.println("t: Triangle wave");
-    Serial.println("q: Square wave");
-    Serial.println("s: Sine wave");
-    Serial.println("r: Sawtooth wave");
-    Serial.println("+: Increase frequency");
-    Serial.println("-: Decrease frequency");
-    
+    // Print list of commands.
+    print_menu();
+
+    // Start generating a sine wave.
     generate_waveform('s');
-    
-    // DAC initialization
-    if (!dac1.begin(AN_RESOLUTION_8, DEFAULT_FREQUENCY * N_SAMPLES, N_SAMPLES, 32)) {
-        Serial.println("Failed to start DAC1 !");
-        while (1);
-    }
 }
 
 void loop() {
     if (Serial.available() > 0) {
         int cmd = Serial.read();
         if (cmd != '\n') {
-          generate_waveform(cmd);
+            generate_waveform(cmd);
         }
     } 
-    
+
     if (dac1.available()) {
         // Get a free buffer for writing.
         SampleBuffer buf = dac1.dequeue();