Diff: main.cpp

Revision:

0:8eeac881ada0

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Mon May 30 15:31:21 2011 +0000
@@ -0,0 +1,73 @@
+#include <mbed.h>
+ 
+// Boolean types
+#define TRUE 1
+#define FALSE 0
+
+/* ADC for the microphone/input, DAC for the speaker/output */
+AnalogIn mic(p19);
+AnalogOut speaker(p18);
+ 
+// Allocate a buffer to be used for the audio recording
+static const size_t   BufferSize = 15 * 1024;
+static unsigned short Buffer[BufferSize];
+ 
+ 
+int main(void)
+{
+    unsigned short        ReadSample = 0xFFFF;
+    // Indices to track where the playback and recording should take place in the
+    // audio buffer.  The recording can occur one sample behind the current playback
+    // index since it is no longer required.
+    int                  Index = 0;
+    // Reverse the direction the buffer is walked between each iteration to save memory
+    int                  Direction = 1;
+    // Have audio to playback
+    int                  Playback = FALSE;
+    // The amount of data to be recorded before starting reverse playback
+    // NOTE: Probably want this to be configured at runtime via a knob, etc.
+    int                  ChunkSize = BufferSize;
+    
+    // Infinite loop of recording and reverse playback
+    for (;;)
+    {
+        unsigned short PlaySample;
+ 
+        // Slow down the sampling rate so that it doesn't exceed 20kHz
+        wait_us(50);
+        
+        // Read out the sample from the buffer to be played back
+        if (Playback)
+        {
+            PlaySample = Buffer[Index];
+            speaker.write_u16(PlaySample);
+        }
+        
+        // Obtain current audio sample from the A/D converter.
+        ReadSample = mic.read_u16();    
+        
+        // Record the sample into the buffer right where a space was freed up from the PlaySample read above
+        Buffer[Index] = ReadSample;
+        
+         // Increment the buffer pointer
+        Index += Direction;
+        
+        // Check to see if the chunk has been filled
+        if (Index < 0)
+        {
+            // Now have a chunk to be played back
+            Playback = TRUE;
+            // Reverse the direction of playback and recording
+            Direction *= -1;
+            Index = 0;
+        }
+        else if (Index >= ChunkSize)
+        {
+            // Now have a chunk to be played back
+            Playback = TRUE;
+            // Reverse the direction of playback and recording
+            Direction *= -1;
+            Index = ChunkSize - 1;
+        }
+    }
+}
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