main.cpp

00001 #include <mbed.h>
00002  
00003 // Boolean types
00004 #define TRUE 1
00005 #define FALSE 0
00006 
00007 //#define NUM_SAMPLES   48000
00008 /* ADC for the microphone/input, DAC for the speaker/output */
00009 AnalogIn mic(p19);
00010 AnalogOut speaker(p18);
00011  
00012 // Allocate a buffer to be used for the audio recording
00013 static const size_t   BufferSize = 10 * 1024;
00014 static unsigned short Buffer[BufferSize];
00015  //   int16_t Buffer[5000];
00016  //unsigned short Buffer[NUM_SAMPLES];
00017  
00018  
00019 int main(void)
00020 {
00021 
00022  //int i;
00023    // for (i = 0; ; )
00024     
00025    { unsigned short        ReadSample = 0xFFFF;
00026     // Indices to track where the playback and recording should take place in the
00027     // audio buffer.  The recording can occur one sample behind the current playback
00028     // index since it is no longer required.
00029     int                  Index = 0;
00030     // Reverse the direction the buffer is walked between each iteration to save memory
00031     int                  Direction = 1;
00032     // Have audio to playback
00033     int                  Playback = FALSE;
00034     // The amount of data to be recorded before starting reverse playback
00035     // NOTE: Probably want this to be configured at runtime via a knob, etc.
00036     int                  ChunkSize = 6024;
00037     
00038     // Infinite loop of recording and reverse playback
00039     for (;;)
00040     {
00041         unsigned short PlaySample;
00042  
00043         // Read out the sample from the buffer to be played back
00044         if (Playback)
00045         {
00046             PlaySample = Buffer[Index];
00047             speaker.write_u16(PlaySample);
00048            // i = (i+0) % NUM_SAMPLES;
00049             
00050            //wait(0.2f);
00051         }
00052         
00053         // Obtain current audio sample from the A/D converter.
00054         // NOTE: I am just faking these values in this sample with an incrementing value
00055         ReadSample = mic.read_u16();    
00056         
00057         // Record the sample into the buffer right where a space was freed up from the PlaySample read above
00058         Buffer[Index] = ReadSample += mic.read_u16();
00059         
00060          // Increment the buffer pointer
00061         Index += Direction;
00062         
00063         // Check to see if the chunk has been filled
00064         if (Index < 0)
00065         {
00066             // Now have a chunk to be played back
00067             Playback = TRUE;
00068             // Reverse the direction of playback and recording
00069             Direction *= -1;
00070             Index = 0;
00071         }
00072         else if (Index >= ChunkSize)
00073         {
00074             // Now have a chunk to be played back
00075             Playback = TRUE;
00076             // Reverse the direction of playback and recording
00077             Direction *= -1;
00078             Index = ChunkSize - 1;
00079         }
00080     }
00081 }
00082 }