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)
00022 {
00023     wave_DAC=_dac;
00024     wave_DAC->write_u16(32768);        //DAC is 0-3.3V, so idles at ~1.6V
00025     verbosity=0;
00026 }
00027 
00028 //-----------------------------------------------------------------------------
00029 // if verbosity is set then wave player enters a mode where the wave file
00030 // is decoded and displayed to the screen, including sample values put into
00031 // the DAC FIFO, and values read out of the DAC FIFO by the ISR.  The DAC output
00032 // itself is so slow as to be unusable, but this might be handy for debugging
00033 // wave files that don't play
00034 //-----------------------------------------------------------------------------
00035 void wave_player::set_verbosity(int v)
00036 {
00037     verbosity=v;
00038 }
00039 
00040 //-----------------------------------------------------------------------------
00041 // player function.  Takes a pointer to an opened wave file.  The file needs
00042 // to be stored in a filesystem with enough bandwidth to feed the wave data.
00043 // LocalFileSystem isn't, but the SDcard is, at least for 22kHz files.  The
00044 // SDcard filesystem can be hotrodded by increasing the SPI frequency it uses
00045 // internally.
00046 //-----------------------------------------------------------------------------
00047 void wave_player::play(FILE *wavefile)
00048 {
00049     unsigned chunk_id,chunk_size,channel;
00050     unsigned data,samp_int,i;
00051     short unsigned dac_data;
00052     long long slice_value;
00053     char *slice_buf;
00054     short *data_sptr;
00055     unsigned char *data_bptr;
00056     int *data_wptr;
00057     FMT_STRUCT wav_format;
00058     long slice,num_slices;
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                     data_sptr=(short *)slice_buf;     // 16 bit samples
00138                     data_bptr=(unsigned char *)slice_buf;     // 8 bit samples
00139                     data_wptr=(int *)slice_buf;     // 32 bit samples
00140                     slice_value=0;
00141                     for (channel=0; channel<wav_format.num_channels; channel++) {
00142                         switch (wav_format.sig_bps) {
00143                             case 16:
00144                                 if (verbosity)
00145                                     printf("16 bit channel %d data=%d ",channel,data_sptr[channel]);
00146                                 slice_value+=data_sptr[channel];
00147                                 break;
00148                             case 32:
00149                                 if (verbosity)
00150                                     printf("32 bit channel %d data=%d ",channel,data_wptr[channel]);
00151                                 slice_value+=data_wptr[channel];
00152                                 break;
00153                             case 8:
00154                                 if (verbosity)
00155                                     printf("8 bit channel %d data=%d ",channel,(int)data_bptr[channel]);
00156                                 slice_value+=data_bptr[channel];
00157                                 break;
00158                         }
00159                     }
00160                     slice_value/=wav_format.num_channels;
00161 
00162 // slice_value is now averaged.  Next it needs to be scaled to an unsigned 16 bit value
00163 // with DC offset so it can be written to the DAC.
00164                     switch (wav_format.sig_bps) {
00165                         case 8:
00166                             slice_value<<=8;
00167                             break;
00168                         case 16:
00169                             slice_value+=32768;
00170                             break;
00171                         case 32:
00172                             slice_value>>=16;
00173                             slice_value+=32768;
00174                             break;
00175                     }
00176                     dac_data=(short unsigned)slice_value;
00177                     if (verbosity)
00178                         printf("sample %d wptr %d slice_value %d dac_data %u\n",slice,DAC_wptr,(int)slice_value,dac_data);
00179                     DAC_fifo[DAC_wptr]=dac_data;
00180                     DAC_wptr=(DAC_wptr+1) & 0xff;
00181                     while (DAC_wptr==DAC_rptr) {
00182                     }
00183                 }
00184                 DAC_on=0;
00185                 tick.detach();
00186                 free(slice_buf);
00187                 break;
00188             case 0x5453494c:
00189                 if (verbosity)
00190                     printf("INFO chunk, size %d\n",chunk_size);
00191                 fseek(wavefile,chunk_size,SEEK_CUR);
00192                 break;
00193             default:
00194                 printf("unknown chunk type 0x%x, size %d\n",chunk_id,chunk_size);
00195                 data=fseek(wavefile,chunk_size,SEEK_CUR);
00196                 break;
00197         }
00198         fread(&chunk_id,4,1,wavefile);
00199         fread(&chunk_size,4,1,wavefile);
00200     }
00201 }
00202 
00203 
00204 void wave_player::dac_out()
00205 {
00206     if (DAC_on) {
00207 #ifdef VERBOSE
00208         printf("ISR rdptr %d got %u\n",DAC_rptr,DAC_fifo[DAC_rptr]);
00209 #endif
00210         wave_DAC->write_u16(DAC_fifo[DAC_rptr]);
00211         DAC_rptr=(DAC_rptr+1) & 0xff;
00212     }
00213 }
00214