MP3 Player without external hardware MP3 Player without external hardware. A software based MP3 player based on a modified version of libmad. Mono output (at the moment) via AnalogOut. Files are read from an USB drive. This is a demo program, it plays only one file at the moment. Documentation is in "main.cpp" and "config.h"
main.cpp
00001 /* This file demonstrates the use of the modified libmad library on LPC1768 00002 * Changes to the library are documented in config.h. 00003 * 00004 * The main change is to use parts of the AHB RAM dedicated to the ethernet module, 00005 * because standard RAM is not sufficient for decoding. 00006 * This means the ethernet module cannot be used !!! 00007 * 00008 * It plays a file "test.mp3" from an external USB-drive/USB-stick. 00009 * For wiring of the USB-connector, see mbed.org 00010 * ID3 decoding is not present at the moment and will cause warnings 00011 * on stderr, and some short noise at the beginning or end of playback. 00012 * 00013 * Output is only for one channel on the DAC (AnalogOut) pin. 00014 * (For connections see datasheets/mbed.org) 00015 * This pin should be decoupled with a capacitor (100u or so) to remove DC. 00016 * The output current is high enough to drive small headphones or active 00017 * speakers directly. 00018 * 00019 * Schematic: :-) 00020 * MBED Pin 18 (AOut) o--||--o Headphone Left 00021 * MBED Pin 1 (GND) o------o Headphone Common 00022 * 00023 * It has been tested with fixed bitrate MP3's up to 320kbps and VBR files. 00024 * 00025 * The remaining RAM is very limited, so don't overuse it ! 00026 * The MSCFileSystem library from mbed.org is needed ! 00027 * Last warning: the main include file "mad.h" maybe not up to date, 00028 * use "decoder.h" for now 00029 * Have fun, 00030 * Andreas Gruen 00031 * *** Version 3: *** 00032 * moved another memory block into AHB RAM, giving more room for 00033 * stereo buffer. 00034 * moved content of decode() to main() 00035 * decoding is now safe to be called multiple times (bug in older versions) 00036 * Output routine now fills stereo buffer, DAC output sums channels, 00037 * just for demonstration that stereo output could go here 00038 */ 00039 00040 #include "mbed.h" 00041 # include "decoder.h" 00042 00043 FILE *fp; 00044 #include "MSCFileSystem.h" 00045 MSCFileSystem fs("usb"); 00046 00047 static enum mad_flow input(void *data,struct mad_stream *stream); 00048 static enum mad_flow output(void *data,struct mad_header const *header,struct mad_pcm *pcm); 00049 static enum mad_flow error_fn(void *data,struct mad_stream *stream,struct mad_frame *frame); 00050 00051 struct dacout_s { 00052 unsigned short l; 00053 unsigned short r; 00054 }; 00055 00056 volatile dacout_s dacbuf[1152]; 00057 volatile dacout_s *dac_s, *dac_e; 00058 00059 AnalogOut dac(p18); 00060 Ticker dacclk; 00061 00062 void dacout(void) 00063 { 00064 if(dac_s < dac_e) 00065 { 00066 dac.write_u16((dac_s->l/2)+(dac_s->r/2)); 00067 dac_s++; 00068 } 00069 } 00070 00071 int main(int argc, char *argv[]) 00072 { 00073 int result; 00074 Timer t; 00075 struct mad_decoder decoder; 00076 00077 dac_s = dac_e = dacbuf; 00078 dacclk.attach_us(dacout,23); 00079 while(1) { 00080 fp = fopen("/usb/test.mp3","rb"); 00081 00082 if(!fp) return(printf("file error\r\n")); 00083 fprintf(stderr,"decode start\r\n"); 00084 mad_decoder_init(&decoder, NULL,input, 0, 0, output,error_fn, 0); 00085 t.reset(); 00086 t.start(); 00087 result = mad_decoder_run(&decoder, MAD_DECODER_MODE_SYNC); 00088 t.stop(); 00089 fprintf(stderr,"decode ret=%d in %d ms\r\n",result,t.read_ms()); 00090 mad_decoder_finish(&decoder); 00091 fclose(fp); 00092 } 00093 return 0; 00094 } 00095 00096 /* 00097 * This is the input callback. The purpose of this callback is to (re)fill 00098 * the stream buffer which is to be decoded. 00099 */ 00100 00101 static 00102 enum mad_flow input(void *data, 00103 struct mad_stream *stream) 00104 { 00105 static unsigned char strmbuff[2100]; 00106 int ret; 00107 int rsz; 00108 unsigned char *bp; 00109 00110 /* the remaining bytes from incomplete frames must be copied 00111 to the beginning of the new buffer ! 00112 */ 00113 bp = strmbuff; 00114 rsz = 0; 00115 if(stream->error == MAD_ERROR_BUFLEN||stream->buffer==NULL) 00116 { 00117 if(stream->next_frame!=NULL) 00118 { 00119 rsz = stream->bufend-stream->next_frame; 00120 memmove(strmbuff,stream->next_frame,rsz); 00121 bp = strmbuff+rsz; 00122 } 00123 } 00124 00125 ret = fread(bp,1,sizeof(strmbuff) - rsz,fp); 00126 00127 if (!ret) 00128 return MAD_FLOW_STOP; 00129 00130 00131 mad_stream_buffer(stream, strmbuff, ret + rsz); 00132 00133 return MAD_FLOW_CONTINUE;} 00134 00135 00136 /* 00137 * The following utility routine performs simple rounding, clipping, and 00138 * scaling of MAD's high-resolution samples down to 16 bits. It does not 00139 * perform any dithering or noise shaping, which would be recommended to 00140 * obtain any exceptional audio quality. It is therefore not recommended to 00141 * use this routine if high-quality output is desired. 00142 */ 00143 00144 static /*inline*/ 00145 signed int scale(mad_fixed_t sample) 00146 { 00147 /* round */ 00148 sample += (1L << (MAD_F_FRACBITS - 16)); 00149 00150 /* clip */ 00151 if (sample >= MAD_F_ONE) 00152 sample = MAD_F_ONE - 1; 00153 else if (sample < -MAD_F_ONE) 00154 sample = -MAD_F_ONE; 00155 00156 /* quantize */ 00157 return sample >> (MAD_F_FRACBITS + 1 - 16); 00158 } 00159 00160 /* 00161 * This is the output callback function. It is called after each frame of 00162 * MPEG audio data has been completely decoded. The purpose of this callback 00163 * is to output (or play) the decoded PCM audio. 00164 */ 00165 00166 static 00167 enum mad_flow output(void *data, 00168 struct mad_header const *header, 00169 struct mad_pcm *pcm) 00170 { 00171 unsigned int nchannels, nsamples; 00172 mad_fixed_t const *left_ch, *right_ch; 00173 00174 00175 /* pcm->samplerate contains the sampling frequency */ 00176 nchannels = pcm->channels; 00177 nsamples = pcm->length; 00178 left_ch = pcm->samples[0]; 00179 right_ch = pcm->samples[1]; 00180 00181 while(dac_s < dac_e) wait_us(1); 00182 dac_e = dacbuf; // potential thread problem ?? no... 00183 dac_s = dacbuf; 00184 00185 while (nsamples--) { 00186 signed int sample_l,sample_r; 00187 sample_l = scale(*left_ch); 00188 sample_r = scale(*right_ch); 00189 dac_e->l = sample_l +32768; 00190 dac_e->r = sample_r +32768; 00191 dac_e++; 00192 left_ch++; 00193 right_ch++; 00194 } 00195 return MAD_FLOW_CONTINUE; 00196 } 00197 00198 /* 00199 * This is the error callback function. It is called whenever a decoding 00200 * error occurs. The error is indicated by stream->error; the list of 00201 * possible MAD_ERROR_* errors can be found in the mad.h (or stream.h) 00202 * header file. 00203 */ 00204 00205 static 00206 enum mad_flow error_fn(void *data, 00207 struct mad_stream *stream, 00208 struct mad_frame *frame) 00209 { 00210 /* ID3 tags will cause warnings and short noise, ignore it for the moment*/ 00211 00212 fprintf(stderr, "decoding error 0x%04x (%s)\n", 00213 stream->error, mad_stream_errorstr(stream)); 00214 00215 00216 /* return MAD_FLOW_BREAK here to stop decoding (and propagate an error) */ 00217 00218 return MAD_FLOW_CONTINUE; 00219 } 00220 00221
Generated on Tue Jul 12 2022 23:11:09 by 1.7.2