main.cpp

00001 #include <mbed.h>
00002 
00003 // Function to power down magic USB interface chip with new firmware
00004 #define USR_POWERDOWN    (0x104)
00005 int semihost_powerdown() {
00006     uint32_t arg;
00007     return __semihost(USR_POWERDOWN, &arg);
00008 }
00009 
00010 // If you don't need the PC host USB interface....
00011 // Power down magic USB interface chip - saves around 150mW
00012 // Needs new firmware (URL below) and USB cable not connected
00013 // http://mbed.org/users/simon/notebook/interface-powerdown/
00014 // Supply power to mbed using Vin pin
00015 
00016  
00017 // Boolean types
00018 #define TRUE 1
00019 #define FALSE 0
00020 
00021 //#define NUM_SAMPLES   48000
00022 /* ADC for the microphone/input, DAC for the speaker/output */
00023 AnalogIn mic(p19);
00024 AnalogOut speaker(p18);
00025  
00026 // Allocate a buffer to be used for the audio recording
00027 static const size_t   BufferSize = 15 * 1066;
00028 static unsigned short Buffer[BufferSize];
00029     //int16_t Buffer[ 32768];
00030  //unsigned short Buffer[NUM_SAMPLES];
00031  
00032  
00033 int main(void)
00034 {
00035 
00036     int result;
00037     result = semihost_powerdown();
00038  //int i;
00039    // for (i = 0; ; )
00040     
00041    { unsigned short        ReadSample = 0xFFFF;
00042     // Indices to track where the playback and recording should take place in the
00043     // audio buffer.  The recording can occur one sample behind the current playback
00044     // index since it is no longer required.
00045     int                  Index = 0;
00046     // Reverse the direction the buffer is walked between each iteration to save memory
00047     int                  Direction = 1;
00048     // Have audio to playback
00049     int                  Playback = FALSE;
00050     // The amount of data to be recorded before starting reverse playback
00051     // NOTE: Probably want this to be configured at runtime via a knob, etc.
00052     //int                  ChunkSize = 9024;
00053         int                  ChunkSize = BufferSize;
00054     // Infinite loop of recording and reverse playback
00055     for (;;)
00056     {
00057         unsigned short PlaySample;
00058  
00059         // Read out the sample from the buffer to be played back
00060         if (Playback)
00061         {
00062             PlaySample = Buffer[Index];
00063             speaker.write_u16(PlaySample);
00064             //i = (i+0) % NUM_SAMPLES;
00065             
00066            //wait(0.2f);
00067         }
00068         
00069         // Obtain current audio sample from the A/D converter.
00070         // NOTE: I am just faking these values in this sample with an incrementing value
00071         ReadSample = mic.read_u16();    
00072         
00073         // Record the sample into the buffer right where a space was freed up from the PlaySample read above
00074         Buffer[Index] = ReadSample += mic.read_u16();
00075         
00076          // Increment the buffer pointer
00077         Index += Direction;
00078         
00079         // Check to see if the chunk has been filled
00080         if (Index < 0)
00081         {
00082             // Now have a chunk to be played back
00083             Playback = TRUE;
00084             // Reverse the direction of playback and recording
00085             Direction *= -1;
00086             Index = 0;
00087         }
00088         else if (Index >= ChunkSize)
00089         {
00090             // Now have a chunk to be played back
00091             Playback = TRUE;
00092             // Reverse the direction of playback and recording
00093             Direction *= -1;
00094             Index = ChunkSize - 1;
00095         }
00096     }
00097 }
00098 }