how to update hw_ptr and appl_ptr

how to update hw_ptr and appl_ptr

[Zhen Fu]

Hi developer,

I recently look the function snd_pcm_update_hw_ptr0 want to  find how to update status->hw_ptr and control->appl_ptr. If you have to know this, can you tell me? Thank you very much.

--
Best Regards,
Zhen Fu

Re: how to update hw_ptr and appl_ptr

[Clemens Ladisch]

Zhen Fu wrote:
> I recently look the function snd_pcm_update_hw_ptr0 want to  find how
> to update status->hw_ptr and control->appl_ptr.

status->hw_ptr is updated by snd_pcm_update_hw_ptr0.  control->appl_ptr
is updated by snd_pcm_lib_write1.

Why are you asking?


Regards,
Clemens

Re: how to update hw_ptr and appl_ptr

[Zhen Fu]

Yes, I know this. I want to know how about updated by snd_pcm_update_hw_ptr0.

--
Best Regards,
Zhen Fu

-----Original Message-----
From: Clemens Ladisch [mailto:clemens@ladisch.de] 
Sent: Tuesday, June 26, 2012 5:35 PM
To: Zhen Fu
Cc: alsa-devel@alsa-project.org
Subject: Re: [alsa-devel] how to update hw_ptr and appl_ptr

Zhen Fu wrote:
> I recently look the function snd_pcm_update_hw_ptr0 want to  find how
> to update status->hw_ptr and control->appl_ptr.

status->hw_ptr is updated by snd_pcm_update_hw_ptr0.  control->appl_ptr
is updated by snd_pcm_lib_write1.

Why are you asking?


Regards,
Clemens

Re: how to update hw_ptr and appl_ptr

[Zhen Fu]

I recently write squ driver and when DMA handler called snd_pcm_period_elapsed, so I want to know how about update hw_ptr in ALSA. 

--
Best Regards,
Zhen Fu


-----Original Message-----
From: Clemens Ladisch [mailto:clemens@ladisch.de] 
Sent: Tuesday, June 26, 2012 5:35 PM
To: Zhen Fu
Cc: alsa-devel@alsa-project.org
Subject: Re: [alsa-devel] how to update hw_ptr and appl_ptr

Zhen Fu wrote:
> I recently look the function snd_pcm_update_hw_ptr0 want to  find how
> to update status->hw_ptr and control->appl_ptr.

status->hw_ptr is updated by snd_pcm_update_hw_ptr0.  control->appl_ptr
is updated by snd_pcm_lib_write1.

Why are you asking?


Regards,
Clemens

Re: how to update hw_ptr and appl_ptr

[Clemens Ladisch]

Zhen Fu wrote:
> when DMA handler called snd_pcm_period_elapsed, so I want to know how
> about update hw_ptr in ALSA.

snd_pcm_period_elapsed() calls snd_pcm_update_hw_ptr0(), which calls
your driver's .pointer callback.  The value returned by that callback
essentially is the hw_ptr (although it doesn't wrap around at the end
of the buffer).

Why do you care about hw_ptr?


Regards,
Clemens

Re: how to update hw_ptr and appl_ptr

[Zhen Fu]

Because when I use aplay playback wav file, appear underrun phenomenon. So I want to ALSA driver how to handle xrun.

--
Best Regards,
Zhen Fu

-----Original Message-----
From: Clemens Ladisch [mailto:clemens@ladisch.de] 
Sent: Tuesday, June 26, 2012 8:27 PM
To: Zhen Fu
Cc: alsa-devel@alsa-project.org
Subject: Re: [alsa-devel] how to update hw_ptr and appl_ptr

Zhen Fu wrote:
> when DMA handler called snd_pcm_period_elapsed, so I want to know how
> about update hw_ptr in ALSA.

snd_pcm_period_elapsed() calls snd_pcm_update_hw_ptr0(), which calls
your driver's .pointer callback.  The value returned by that callback
essentially is the hw_ptr (although it doesn't wrap around at the end
of the buffer).

Why do you care about hw_ptr?


Regards,
Clemens

Re: how to update hw_ptr and appl_ptr

[Clemens Ladisch]

A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

Zhen Fu wrote:
> Because when I use aplay playback wav file, appear underrun phenomenon. So I want to ALSA driver how to handle xrun.

The most likely reason is that the .pointer callback returns wrong values.


Regards,
Clemens