wave_player.cpp

00001 //-----------------------------------------------------------------------------
00002 // a sample mbed library to play back wave files.
00003 //
00004 // explanation of wave file format.
00005 // https://ccrma.stanford.edu/courses/422/projects/WaveFormat/
00006 
00007 // if VERBOSE is uncommented then the wave player will enter a verbose
00008 // mode that displays all data values as it reads them from the file
00009 // and writes them to the DAC.  Very slow and unusable output on the DAC,
00010 // but useful for debugging wave files that don't work.
00011 //#define VERBOSE
00012 
00013 
00014 #include <mbed.h>
00015 #include <stdio.h>
00016 #include <wave_player.h>
00017 int g_volume = 0;
00018 //-----------------------------------------------------------------------------
00019 // constructor -- accepts an mbed pin to use for AnalogOut.  Only p18 will work
00020 wave_player::wave_player(AnalogOut *_dac)
00021 {
00022   wave_DAC=_dac;
00023   wave_DAC->write_u16(32768);        //DAC is 0-3.3V, so idles at ~1.6V
00024   verbosity=0;
00025 }
00026 
00027 //-----------------------------------------------------------------------------
00028 // if verbosity is set then wave player enters a mode where the wave file
00029 // is decoded and displayed to the screen, including sample values put into
00030 // the DAC FIFO, and values read out of the DAC FIFO by the ISR.  The DAC output
00031 // itself is so slow as to be unusable, but this might be handy for debugging
00032 // wave files that don't play
00033 //-----------------------------------------------------------------------------
00034 void wave_player::set_verbosity(int v)
00035 {
00036   verbosity=v;
00037 }
00038 
00039 //-----------------------------------------------------------------------------
00040 // player function.  Takes a pointer to an opened wave file.  The file needs
00041 // to be stored in a filesystem with enough bandwidth to feed the wave data.
00042 // LocalFileSystem isn't, but the SDcard is, at least for 22kHz files.  The
00043 // SDcard filesystem can be hotrodded by increasing the SPI frequency it uses
00044 // internally.
00045 //-----------------------------------------------------------------------------
00046 void wave_player::play(FILE *wavefile, int *startStop, int *volume)
00047 {
00048         unsigned chunk_id,chunk_size,channel;
00049         unsigned data,samp_int,i;
00050         short unsigned dac_data;
00051         long long slice_value;
00052         char *slice_buf;
00053         short *data_sptr;
00054         unsigned char *data_bptr;
00055         int *data_wptr;
00056         FMT_STRUCT wav_format;
00057         long slice,num_slices;
00058         
00059   DAC_wptr=0;
00060   DAC_rptr=0;
00061   for (i=0;i<256;i+=2) {
00062     DAC_fifo[i]=0;
00063     DAC_fifo[i+1]=3000;
00064   }
00065   DAC_wptr=4;
00066   DAC_on=0;
00067 
00068   fread(&chunk_id,4,1,wavefile);
00069   fread(&chunk_size,4,1,wavefile);
00070   while (!feof(wavefile)) {
00071     if (verbosity)
00072       printf("Read chunk ID 0x%x, size 0x%x\n",chunk_id,chunk_size);
00073     switch (chunk_id) {
00074       case 0x46464952:
00075         fread(&data,4,1,wavefile);
00076         if (verbosity) {
00077           printf("RIFF chunk\n");
00078           printf("  chunk size %d (0x%x)\n",chunk_size,chunk_size);
00079           printf("  RIFF type 0x%x\n",data);
00080         }
00081         break;
00082       case 0x20746d66:
00083         fread(&wav_format,sizeof(wav_format),1,wavefile);
00084         if (verbosity) {
00085           printf("FORMAT chunk\n");
00086           printf("  chunk size %d (0x%x)\n",chunk_size,chunk_size);
00087           printf("  compression code %d\n",wav_format.comp_code);
00088           printf("  %d channels\n",wav_format.num_channels);
00089           printf("  %d samples/sec\n",wav_format.sample_rate);
00090           printf("  %d bytes/sec\n",wav_format.avg_Bps);
00091           printf("  block align %d\n",wav_format.block_align);
00092           printf("  %d bits per sample\n",wav_format.sig_bps);
00093         }
00094         if (chunk_size > sizeof(wav_format))
00095           fseek(wavefile,chunk_size-sizeof(wav_format),SEEK_CUR);
00096         break;
00097       case 0x61746164:
00098 // allocate a buffer big enough to hold a slice
00099         slice_buf=(char *)malloc(wav_format.block_align);
00100         if (!slice_buf) {
00101           printf("Unable to malloc slice buffer");
00102           exit(1);
00103         }
00104         num_slices=chunk_size/wav_format.block_align;
00105         samp_int=1000000/(wav_format.sample_rate);
00106         if (verbosity) {
00107           printf("DATA chunk\n");
00108           printf("  chunk size %d (0x%x)\n",chunk_size,chunk_size);
00109           printf("  %d slices\n",num_slices);
00110           printf("  Ideal sample interval=%d\n",(unsigned)(1000000.0/wav_format.sample_rate));
00111           printf("  programmed interrupt tick interval=%d\n",samp_int);
00112         }
00113 
00114 // starting up ticker to write samples out -- no printfs until tick.detach is called
00115         if (verbosity)
00116           tick.attach_us(this,&wave_player::dac_out, 500000); 
00117         else
00118           tick.attach_us(this,&wave_player::dac_out, samp_int); 
00119         DAC_on=1; 
00120 
00121 // start reading slices, which contain one sample each for however many channels
00122 // are in the wave file.  one channel=mono, two channels=stereo, etc.  Since
00123 // mbed only has a single AnalogOut, all of the channels present are averaged
00124 // to produce a single sample value.  This summing and averaging happens in
00125 // a variable of type signed long long, to make sure that the data doesn't
00126 // overflow regardless of sample size (8 bits, 16 bits, 32 bits).
00127 //
00128 // note that from what I can find that 8 bit wave files use unsigned data,
00129 // while 16 and 32 bit wave files use signed data
00130 //
00131         for (slice=0;slice<num_slices;slice+=1) {
00132           fread(slice_buf,wav_format.block_align,1,wavefile);
00133           if (feof(wavefile)) {
00134             printf("Oops -- not enough slices in the wave file\n");
00135             exit(1);
00136           }
00137           //exit when user stops song
00138            if (*startStop == 0){
00139                 break;
00140             }
00141             //pass volume to dac_out
00142             g_volume = *volume;
00143             
00144           data_sptr=(short *)slice_buf;     // 16 bit samples
00145           data_bptr=(unsigned char *)slice_buf;     // 8 bit samples
00146           data_wptr=(int *)slice_buf;     // 32 bit samples
00147           slice_value=0;
00148           for (channel=0;channel<wav_format.num_channels;channel++) {
00149             switch (wav_format.sig_bps) {
00150               case 16:
00151                 if (verbosity)
00152                   printf("16 bit channel %d data=%d ",channel,data_sptr[channel]);
00153                 slice_value+=data_sptr[channel];
00154                 break;
00155               case 32:
00156                 if (verbosity)
00157                   printf("32 bit channel %d data=%d ",channel,data_wptr[channel]);
00158                 slice_value+=data_wptr[channel];
00159                 break;
00160               case 8:
00161                 if (verbosity)
00162                   printf("8 bit channel %d data=%d ",channel,(int)data_bptr[channel]);
00163                 slice_value+=data_bptr[channel];
00164                 break;
00165             }
00166           }
00167           slice_value/=wav_format.num_channels;
00168           
00169 // slice_value is now averaged.  Next it needs to be scaled to an unsigned 16 bit value
00170 // with DC offset so it can be written to the DAC.
00171           switch (wav_format.sig_bps) {
00172             case 8:     slice_value<<=8;
00173                         break;
00174             case 16:    slice_value+=32768;
00175                         break;
00176             case 32:    slice_value>>=16;
00177                         slice_value+=32768;
00178                         break;
00179           }
00180           dac_data=(short unsigned)slice_value;
00181           if (verbosity)
00182             printf("sample %d wptr %d slice_value %d dac_data %u\n",slice,DAC_wptr,(int)slice_value,dac_data);
00183           DAC_fifo[DAC_wptr]=dac_data;
00184           DAC_wptr=(DAC_wptr+1) & 0xff;
00185           while (DAC_wptr==DAC_rptr) {
00186           }
00187         }
00188         DAC_on=0;
00189         tick.detach();
00190         free(slice_buf);
00191         break;
00192       case 0x5453494c:
00193         if (verbosity)
00194           printf("INFO chunk, size %d\n",chunk_size);
00195         fseek(wavefile,chunk_size,SEEK_CUR);
00196         break;
00197       default:
00198         printf("unknown chunk type 0x%x, size %d\n",chunk_id,chunk_size);
00199         data=fseek(wavefile,chunk_size,SEEK_CUR);
00200         break;
00201     }
00202     fread(&chunk_id,4,1,wavefile);
00203     fread(&chunk_size,4,1,wavefile);
00204 
00205   }
00206 }
00207 
00208 
00209 void wave_player::dac_out()
00210 {
00211   if (DAC_on) {
00212 #ifdef VERBOSE
00213   printf("ISR rdptr %d got %u\n",DAC_rptr,DAC_fifo[DAC_rptr]);
00214 #endif
00215 
00216     wave_DAC->write_u16((DAC_fifo[DAC_rptr]*(16 - g_volume))>>4);
00217     DAC_rptr=(DAC_rptr+1) & 0xff;
00218   }
00219 }
00220