Only 5 signals are required to control the DSP VS1002.

1. Legacy SPI signals i.e. CLK, DI, DO, CS for data transmission,
2. DREQ signal for frame flow control from DSP VS1002,
3. an extra signal xCS for control DSP VS1002 functions and read various status.

First Enable theses option inside kernel
CONFIG_ETRAX_SYNCHRONOUS_SERIAL=y
CONFIG_ETRAX_SYNCHRONOUS_SERIAL_PORT1=y
CONFIG_ETRAX_SYNCHRONOUS_SERIAL1_DMA=y

This small code snippet tests sending mp3 data's over the SPI bus with Frame (DREQ VS1002 signal) flow control.

  FILE *file;
  unsigned char buf[2048];
 
......
 
  if ((fd = open ("/dev/syncser1", O_RDWR )) < 0)
    {
      fprintf (stderr, "Failed to open syncser1\n");
      exit (1);
    }
  fprintf (stderr, "syncser1 open\n\n");
 
  ioctl (fd, SSP_SPI, SPI_MASTER);
 
  if (ioctl (fd, SSP_SPEED, SSP3125000))
    {
      fprintf (stderr, "Couldn't change sync SSP_SPEED\n");
      err++;
    }
 
  if (ioctl (fd, SSP_INBUFCHUNK, 8192))
    {
      fprintf (stderr, "Couldn't change sync SSP_BUFCHUNK\n");
      err++;
    }
  fprintf (stderr, "Running ...\n");
 
  tmp = NORMAL_SYNC | WORD_SYNC | SYNC_ON |
    WORD_SIZE_8 | BIT_ORDER_MSB | FLOW_CONTROL_ENABLE | CLOCK_NOT_GATED;
 
  if (ioctl (fd, SSP_FRAME_SYNC, tmp))
    {
      fprintf (stderr, "Couldn't change sync SSP_FRAME_SYNC\n");
      err++;
    }
 
 fprintf (stderr, "xDCS = 0\n");
 
  tmp = CLOCK_INVERT | FRAME_INVERT | STATUS_INVERT;
  if (ioctl (fd, SSP_IPOLARITY, tmp))
    {
      fprintf (stderr, "Couldn't change polarity SSP_IPOLARITY\n");
      err++;
    }
 
  tmp = CLOCK_INVERT | FRAME_INVERT | STATUS_INVERT;
  if (ioctl (fd, SSP_OPOLARITY, tmp))
    {
      fprintf (stderr, "Couldn't change polarity SSP_OPOLARITY\n");
      err++;
    }
 
  /* Open mp3 file (usage : "mp3play -p < file.mp3" */
  if((df=fileno(stdin))==-1)
    {
      fprintf(stderr, "Unknow file\n");
      exit(1);
    }
  fprintf(stderr, "Open mp3 file \n");
 
  file = fdopen(df, "r");
 
  fprintf (stderr, "Playing ...\n");
 
  size = write(fd, 0, 2048);
  fprintf (stderr, "Sending 0x00 \n");
 
  while(!feof(file))
  {
    n =  fread(buf, 1, sizeof(buf), file);
   //	  fprintf (stderr, "Blocs read %d \n", n);
 
    size = write(fd, buf, sizeof(buf));
   //	  fprintf (stderr, "Write bloc %d \n", size);
   }
      fprintf (stderr, "End playing \n");
 
  close(fd);
  fclose(file);
  exit(1);
}

Drop me a mail : habib.bouaziz@gmail.com

Report on top -d 1

Mem: 9400K used, 5568K free, 0K shrd, 0K buff, 5696K cached Load average: 0.00, 0.00, 0.00 (State: S=sleeping R=running, W=waiting)

PID USER     STATUS   RSS  PPID %CPU %MEM COMMAND
156 root     R        840   110  8.1  5.6 top
 85 root     S        480     1  2.7  3.2 utelnetd
 51 root     S        496     1  0.6  3.3 respawnd
147 root     S        424   110  0.6  2.8 mp3play
 54 root     S        728     1  0.0  4.8 syslogd
100 root     S        704     1  0.0  4.7 boa
110 root     S        696    85  0.0  4.6 sh
106 root     S        680     1  0.0  4.5 udhcpc
104 root     S        624     1  0.0  4.1 sh
 91 root     S        520     1  0.0  3.4 vftpd
 57 root     S        488     1  0.0  3.2 klogd
  1 root     S        432     0  0.0  2.8 init
  7 root     SW         0     1  0.0  0.0 mtdblockd
  2 root     SW         0     1  0.0  0.0 keventd
  3 root     SWN        0     1  0.0  0.0 ksoftirqd_CPU0
  4 root     SW         0     1  0.0  0.0 kswapd
  5 root     SW         0     1  0.0  0.0 bdflush
  6 root     SW         0     1  0.0  0.0 kupdated

The relevant process
147 root S 424 110 0.6 2.8 mp3play
does not exceed 0.8% CPU with any mp3 rate between [32Kbits/s .. 192Kbits/s]. Surprising isn”t it ?

Habib Bouaziz-Viallet (Friends of mine often they call me Bib)