[alsa-devel] trace PCM data from usb bus to alsa lib

[ZeroCluo]

Hi 

  I am trying to trace the Audio data from usb bus.
in kernel: 
dump data in retire_capture_urb() ,found data format is like:
AABB 0000 CCDD 0000 ;

but in alsa library ,
dump data in snd_pcm_mmap_begin(),the "0000" is cut,only "AABB CCDD",

Do you know when and where those "0000" is cut?

btw,use mmap method map dma_area to user space; and use snd_pcm_readi to get 
audio data;

Thank you very very much.

Best Regards,
Zero