Diff: main.cpp

Revision:

0:7627c79db971

Child:

2:f28cf0afd021

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Fri Nov 26 12:18:30 2010 +0000
@@ -0,0 +1,237 @@
+/* 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;
+}
+
+