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
- Committer:
- Gruenfrosch
- Date:
- 2010-11-26
- Revision:
- 1:7c923cbe9f1d
- Parent:
- 0:7627c79db971
- Child:
- 2:f28cf0afd021
File content as of revision 1:7c923cbe9f1d:
/* This file demonstrates the use of the modified libmad library on LPC1768 * Changes to the library are documented in config.h. * * The main change is to use parts of the AHB RAM dedicated to the ethernet module, * because standard RAM is not sufficient for decoding. * This means the ethernet module cannot be used !!! * * It plays a file "test.mp3" from an external USB-drive/USB-stick. * For wiring of the USB-connector, see mbed.org * ID3 decoding is not present at the moment and will cause warnings * on stderr, and some short noise at the beginning or end of playback. * * Output is only for one channel on the DAC (AnalogOut) pin. * (For connections see datasheets/mbed.org) * This pin should be decoupled with a capacitor (100u or so) to remove DC. * The output current is high enough to drive small headphones or active * speakers directly. * * Schematic: :-) * MBED Pin 18 (AOut) o--||--o Headphone Left * MBED Pin 1 (GND) o------o Headphone Common * * It has been tested with fixed bitrate MP3's up to 320kbps and VBR files. * * The remaining RAM is very limited, so don't overuse it ! * The MSCFileSystem library from mbed.org is needed ! * Last warning: the main include file "mad.h" maybe not up to date, * use "decoder.h" for now * Have fun, * Andreas Gruen */ #include "mbed.h" # include "decoder.h" static int decode(void); FILE *fp; #include "MSCFileSystem.h" MSCFileSystem fs("usb"); volatile unsigned short dacbuf[1200]; volatile unsigned short *dac_s, *dac_e; AnalogOut dac(p18); Ticker dacclk; void dacout(void) { if(dac_s < dac_e) { dac.write_u16(*dac_s++); } } int main(int argc, char *argv[]) { int ret; Timer t; dac_s = dac_e = dacbuf; dacclk.attach_us(dacout,23); fp = fopen("/usb/test.mp3","rb"); if(!fp) return(printf("no file\r\n")); t.start(); ret = decode(); t.stop(); printf("decode ret=%d in %d ms\r\n",ret,t.read_ms()); fclose(fp); return 0; } /* * This is the input callback. The purpose of this callback is to (re)fill * the stream buffer which is to be decoded. */ static enum mad_flow input(void *data, struct mad_stream *stream) { static unsigned char strmbuff[2100]; int ret; int rsz; unsigned char *bp; /* the remaining bytes from incomplete frames must be copied to the beginning of the new buffer ! */ bp = strmbuff; rsz = 0; if(stream->error == MAD_ERROR_BUFLEN||stream->buffer==NULL) { if(stream->next_frame!=NULL) { rsz = stream->bufend-stream->next_frame; memmove(strmbuff,stream->next_frame,rsz); bp = strmbuff+rsz; } } ret = fread(bp,1,sizeof(strmbuff) - rsz,fp); if (!ret) return MAD_FLOW_STOP; mad_stream_buffer(stream, strmbuff, ret + rsz); return MAD_FLOW_CONTINUE;} /* * The following utility routine performs simple rounding, clipping, and * scaling of MAD's high-resolution samples down to 16 bits. It does not * perform any dithering or noise shaping, which would be recommended to * obtain any exceptional audio quality. It is therefore not recommended to * use this routine if high-quality output is desired. */ static /*inline*/ signed int scale(mad_fixed_t sample) { /* round */ sample += (1L << (MAD_F_FRACBITS - 16)); /* clip */ if (sample >= MAD_F_ONE) sample = MAD_F_ONE - 1; else if (sample < -MAD_F_ONE) sample = -MAD_F_ONE; /* quantize */ return sample >> (MAD_F_FRACBITS + 1 - 16); } /* * This is the output callback function. It is called after each frame of * MPEG audio data has been completely decoded. The purpose of this callback * is to output (or play) the decoded PCM audio. */ static enum mad_flow output(void *data, struct mad_header const *header, struct mad_pcm *pcm) { unsigned int nchannels, nsamples; mad_fixed_t const *left_ch, *right_ch; /* pcm->samplerate contains the sampling frequency */ nchannels = pcm->channels; nsamples = pcm->length; left_ch = pcm->samples[0]; right_ch = pcm->samples[1]; while(dac_s < dac_e) wait_us(10); dac_e = dacbuf; // potential thread problem ?? dac_s = dacbuf; while (nsamples--) { signed int sample; /* output sample(s) in 16-bit signed little-endian PCM */ sample = scale(*left_ch++); *dac_e++ = sample +32700; //putchar((sample >> 0) & 0xff); //putchar((sample >> 8) & 0xff); /* the second channel is not supported at the moment*/ if (nchannels == 2) { sample = scale(*right_ch++); //putchar((sample >> 0) & 0xff); //putchar((sample >> 8) & 0xff); } } return MAD_FLOW_CONTINUE; } /* * This is the error callback function. It is called whenever a decoding * error occurs. The error is indicated by stream->error; the list of * possible MAD_ERROR_* errors can be found in the mad.h (or stream.h) * header file. */ static enum mad_flow error_fn(void *data, struct mad_stream *stream, struct mad_frame *frame) { /* ID3 tags will cause warnings and short noise, ignore it for the moment*/ fprintf(stderr, "decoding error 0x%04x (%s)\n", stream->error, mad_stream_errorstr(stream)); /* return MAD_FLOW_BREAK here to stop decoding (and propagate an error) */ return MAD_FLOW_CONTINUE; } /* * This is the function called by main() above to perform all the decoding. * It instantiates a decoder object and configures it with the input, * output, and error callback functions above. A single call to * mad_decoder_run() continues until a callback function returns * MAD_FLOW_STOP (to stop decoding) or MAD_FLOW_BREAK (to stop decoding and * signal an error). */ static int decode() { struct mad_decoder decoder; int result; /* configure input, output, and error functions */ mad_decoder_init(&decoder, NULL, input, 0 /* header */, 0 /* filter */, output, error_fn, 0 /* message */); /* start decoding */ result = mad_decoder_run(&decoder, MAD_DECODER_MODE_SYNC); /* release the decoder */ mad_decoder_finish(&decoder); return result; }