snd_pcm_open:open()->snd_open()(sound.c)->snd_pcm_playback_open()
snd_pcm_params_any:
snd_pcm_hw_params_set_xx
snd_pcm_hw_params:
snd_pcm_sw_params:
snd_pcm_prepare:
snd_pcm_writei:
snd_pcm_drop:
snd_pcm_close:
