trace PCM data from usb bus to alsa lib

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

Re: trace PCM data from usb bus to alsa lib

[Takashi Iwai]

At Wed, 17 Jun 2009 07:25:25 +0000 (UTC),
ZeroCluo wrote:
> 
> 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?

Are you using the native format that the hardware runs?


Takashi

Re: trace PCM data from usb bus to alsa lib

[Takashi Iwai]

At Wed, 17 Jun 2009 16:10:26 +0800,
Zero Luo wrote:
> 
> Dear Takashi,
>  
>    Data from usb dongle is 16K*16 bit PCM data.

And what is the format and channels you are using in alsa-lib?
alsa-lib itself can convert formats and channels automatically if needed.


Takashi

> 2009/6/17, Takashi Iwai <tiwai@suse.de>:
> 
>     At Wed, 17 Jun 2009 07:25:25 +0000 (UTC),
>     ZeroCluo wrote:
>     >
>     > 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?
>    
>     Are you using the native format that the hardware runs?
> 
>     Takashi
> 
> 

Re: trace PCM data from usb bus to alsa lib

[ZeroCluo]

Takashi Iwai <tiwai <at> suse.de> writes:

> 
> At Wed, 17 Jun 2009 16:10:26 +0800,
> Zero Luo wrote:
> > 
> > Dear Takashi,
> >  
> >    Data from usb dongle is 16K*16 bit PCM data.
> 
> And what is the format and channels you are using in alsa-lib?
> alsa-lib itself can convert formats and channels automatically if needed.
> 
> Takashi


 In alsa-lib ,I set data format as 8K * mulaw .
        hwparams.format = SND_PCM_FORMAT_MU_LAW;
        hwparams.rate = 8000;
        hwparams.channels = 1;
 Yes,indeed alsa-lib help to convert formats.But before alsa-lib convert pcm 
data to mulaw,I dumped the src data in snd_pcm_mulaw_encode() which already 
has no "0000" .


Zero

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Re: trace PCM data from usb bus to alsa lib

[Takashi Iwai]

At Wed, 17 Jun 2009 08:33:15 +0000 (UTC),
ZeroCluo wrote:
> 
> Takashi Iwai <tiwai <at> suse.de> writes:
> 
> > 
> > At Wed, 17 Jun 2009 16:10:26 +0800,
> > Zero Luo wrote:
> > > 
> > > Dear Takashi,
> > >  
> > >    Data from usb dongle is 16K*16 bit PCM data.
> > 
> > And what is the format and channels you are using in alsa-lib?
> > alsa-lib itself can convert formats and channels automatically if needed.
> > 
> > Takashi
> 
> 
>  In alsa-lib ,I set data format as 8K * mulaw .
>         hwparams.format = SND_PCM_FORMAT_MU_LAW;
>         hwparams.rate = 8000;
>         hwparams.channels = 1;
>  Yes,indeed alsa-lib help to convert formats.But before alsa-lib convert pcm 
> data to mulaw,I dumped the src data in snd_pcm_mulaw_encode() which already 
> has no "0000" .

Well, another question is whether the output result is correct.
Did you get broken output or so?


Takashi

Re: trace PCM data from usb bus to alsa lib

[ZeroCluo]

> Well, another question is whether the output result is correct.
> Did you get broken output or so?
> 
> Takashi
> 


 First,thanks for your reply.

Output should be correct.I can hear smooth voice. It real confuse me...

Zero