/dev/dsp on beagleboard-XM revB

   I have installed the Angstrom system on beaglebord and I did some
audio coding.
   Atfer some work, aplay music.wav finally worked. I programed using
ASLA API such as snd_pcm_writei(handle, data, wcount) and so on to
play a wav-file, the code worked on the beagleboard-XM revB too.I
hear music from headphone.
   But when I used another kind of audio coding:

   fd = open("/dev/dsp", O_WRONLY);
  write(fd, buf, wcount);

  It didn't work on beaglebord, there was no sound from headphone.
  Does the beagleboard not support this kind of audio coding or I
should do some configuration to make /dev/dsp
  Ask for your help.
  Best wishes!