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 
00018 
00019 //-----------------------------------------------------------------------------
00020 // constructor -- accepts an mbed pin to use for AnalogOut.  Only p18 will work
00021 wave_player::wave_player(AnalogOut *_dac, PwmOut *_pwm)
00022 {
00023   wave_PWM = _pwm;
00024   wave_DAC=_dac;
00025   wave_DAC->write_u16(32768);        //DAC is 0-3.3V, so idles at ~1.6V
00026   *wave_PWM = 32768;
00027   verbosity=0;
00028 }
00029 
00030 //-----------------------------------------------------------------------------
00031 // if verbosity is set then wave player enters a mode where the wave file
00032 // is decoded and displayed to the screen, including sample values put into
00033 // the DAC FIFO, and values read out of the DAC FIFO by the ISR.  The DAC output
00034 // itself is so slow as to be unusable, but this might be handy for debugging
00035 // wave files that don't play
00036 //-----------------------------------------------------------------------------
00037 void wave_player::set_verbosity(int v)
00038 {
00039   verbosity=v;
00040 }
00041 
00042 //-----------------------------------------------------------------------------
00043 // player function.  Takes a pointer to an opened wave file.  The file needs
00044 // to be stored in a filesystem with enough bandwidth to feed the wave data.
00045 // LocalFileSystem isn't, but the SDcard is, at least for 22kHz files.  The
00046 // SDcard filesystem can be hotrodded by increasing the SPI frequency it uses
00047 // internally.
00048 //-----------------------------------------------------------------------------
00049 void wave_player::play(FILE *wavefile)
00050 {
00051         unsigned chunk_id,chunk_size,channel;
00052         unsigned data,samp_int,i;
00053         short unsigned dac_data;
00054         long long slice_value;
00055         char *slice_buf;
00056         short *data_sptr;
00057         unsigned char *data_bptr;
00058         int *data_wptr;
00059         FMT_STRUCT wav_format;
00060         long slice,num_slices;
00061   DAC_wptr=0;
00062   DAC_rptr=0;
00063   for (i=0;i<256;i+=2) {
00064     DAC_fifo[i]=0;
00065     DAC_fifo[i+1]=3000;
00066   }
00067   DAC_wptr=4;
00068   DAC_on=0;
00069 
00070   fread(&chunk_id,4,1,wavefile);
00071   fread(&chunk_size,4,1,wavefile);
00072   while (!feof(wavefile)) {
00073     if (verbosity)
00074       printf("Read chunk ID 0x%x, size 0x%x\n",chunk_id,chunk_size);
00075     switch (chunk_id) {
00076       case 0x46464952:
00077         fread(&data,4,1,wavefile);
00078         if (verbosity) {
00079           printf("RIFF chunk\n");
00080           printf("  chunk size %d (0x%x)\n",chunk_size,chunk_size);
00081           printf("  RIFF type 0x%x\n",data);
00082         }
00083         break;
00084       case 0x20746d66:
00085         fread(&wav_format,sizeof(wav_format),1,wavefile);
00086         if (verbosity) {
00087           printf("FORMAT chunk\n");
00088           printf("  chunk size %d (0x%x)\n",chunk_size,chunk_size);
00089           printf("  compression code %d\n",wav_format.comp_code);
00090           printf("  %d channels\n",wav_format.num_channels);
00091           printf("  %d samples/sec\n",wav_format.sample_rate);
00092           printf("  %d bytes/sec\n",wav_format.avg_Bps);
00093           printf("  block align %d\n",wav_format.block_align);
00094           printf("  %d bits per sample\n",wav_format.sig_bps);
00095         }
00096         if (chunk_size > sizeof(wav_format))
00097           fseek(wavefile,chunk_size-sizeof(wav_format),SEEK_CUR);
00098         break;
00099       case 0x61746164:
00100 // allocate a buffer big enough to hold a slice
00101         slice_buf=(char *)malloc(wav_format.block_align);
00102         if (!slice_buf) {
00103           printf("Unable to malloc slice buffer");
00104           exit(1);
00105         }
00106         num_slices=chunk_size/wav_format.block_align;
00107         samp_int=1000000/(wav_format.sample_rate);
00108         if (verbosity) {
00109           printf("DATA chunk\n");
00110           printf("  chunk size %d (0x%x)\n",chunk_size,chunk_size);
00111           printf("  %d slices\n",num_slices);
00112           printf("  Ideal sample interval=%d\n",(unsigned)(1000000.0/wav_format.sample_rate));
00113           printf("  programmed interrupt tick interval=%d\n",samp_int);
00114         }
00115 
00116 // starting up ticker to write samples out -- no printfs until tick.detach is called
00117         if (verbosity)
00118           tick.attach_us(this,&wave_player::dac_out, 500000); 
00119         else
00120           tick.attach_us(this,&wave_player::dac_out, samp_int); 
00121         DAC_on=1; 
00122 
00123 // start reading slices, which contain one sample each for however many channels
00124 // are in the wave file.  one channel=mono, two channels=stereo, etc.  Since
00125 // mbed only has a single AnalogOut, all of the channels present are averaged
00126 // to produce a single sample value.  This summing and averaging happens in
00127 // a variable of type signed long long, to make sure that the data doesn't
00128 // overflow regardless of sample size (8 bits, 16 bits, 32 bits).
00129 //
00130 // note that from what I can find that 8 bit wave files use unsigned data,
00131 // while 16 and 32 bit wave files use signed data
00132 //
00133         for (slice=0;slice<num_slices;slice+=1) {
00134           fread(slice_buf,wav_format.block_align,1,wavefile);
00135           if (feof(wavefile)) {
00136             printf("Oops -- not enough slices in the wave file\n");
00137             exit(1);
00138           }
00139           data_sptr=(short *)slice_buf;     // 16 bit samples
00140           data_bptr=(unsigned char *)slice_buf;     // 8 bit samples
00141           data_wptr=(int *)slice_buf;     // 32 bit samples
00142           slice_value=0;
00143           for (channel=0;channel<wav_format.num_channels;channel++) {
00144             switch (wav_format.sig_bps) {
00145               case 16:
00146                 if (verbosity)
00147                   printf("16 bit channel %d data=%d ",channel,data_sptr[channel]);
00148                 slice_value+=data_sptr[channel];
00149                 break;
00150               case 32:
00151                 if (verbosity)
00152                   printf("32 bit channel %d data=%d ",channel,data_wptr[channel]);
00153                 slice_value+=data_wptr[channel];
00154                 break;
00155               case 8:
00156                 if (verbosity)
00157                   printf("8 bit channel %d data=%d ",channel,(int)data_bptr[channel]);
00158                 slice_value+=data_bptr[channel];
00159                 break;
00160             }
00161           }
00162           slice_value/=wav_format.num_channels;
00163           
00164 // slice_value is now averaged.  Next it needs to be scaled to an unsigned 16 bit value
00165 // with DC offset so it can be written to the DAC.
00166           switch (wav_format.sig_bps) {
00167             case 8:     slice_value<<=8;
00168                         break;
00169             case 16:    slice_value+=32768;
00170                         break;
00171             case 32:    slice_value>>=16;
00172                         slice_value+=32768;
00173                         break;
00174           }
00175           dac_data=(short unsigned)slice_value;
00176           if (verbosity)
00177             printf("sample %d wptr %d slice_value %d dac_data %u\n",slice,DAC_wptr,(int)slice_value,dac_data);
00178           DAC_fifo[DAC_wptr]=dac_data;
00179           DAC_wptr=(DAC_wptr+1) & 0xff;
00180           while (DAC_wptr==DAC_rptr) {
00181           }
00182         }
00183         DAC_on=0;
00184         tick.detach();
00185         free(slice_buf);
00186         break;
00187       case 0x5453494c:
00188         if (verbosity)
00189           printf("INFO chunk, size %d\n",chunk_size);
00190         fseek(wavefile,chunk_size,SEEK_CUR);
00191         break;
00192       default:
00193         printf("unknown chunk type 0x%x, size %d\n",chunk_id,chunk_size);
00194         data=fseek(wavefile,chunk_size,SEEK_CUR);
00195         break;
00196     }
00197     fread(&chunk_id,4,1,wavefile);
00198     fread(&chunk_size,4,1,wavefile);
00199   }
00200 }
00201 
00202 
00203 void wave_player::dac_out()
00204 {
00205   if (DAC_on) {
00206 #ifdef VERBOSE
00207   printf("ISR rdptr %d got %u\n",DAC_rptr,DAC_fifo[DAC_rptr]);
00208 #endif
00209     wave_DAC->write_u16(DAC_fifo[DAC_rptr]);
00210     wave_PWM->write(float(DAC_fifo[DAC_rptr]/65536.0));
00211     DAC_rptr=(DAC_rptr+1) & 0xff;
00212   }
00213 }