Application supporting forward/rewind APIs

Application supporting forward/rewind APIs

[Anuj Aggarwal]

Hi,

I want to try the forward/rewind APIs supported by the ALSA library.
Can someone point to an ALSA application which exercises these APIs?

Best Regards,
Anuj Aggarwal

Re: Application supporting forward/rewind APIs

[Takashi Iwai]

At Thu, 24 Sep 2009 13:04:24 +0530,
Anuj Aggarwal wrote:
> 
> Hi,
> 
> I want to try the forward/rewind APIs supported by the ALSA library.
> Can someone point to an ALSA application which exercises these APIs?

Pulseaudio is using snd_pcm_rewind().
About snd_pcm_forward(), I don't know of...


Takashi

Re: Application supporting forward/rewind APIs

[Raymond Yau]

Do you mean that there is no test program to verify the implementation is
correct ?

Some sound card 's hardware has FIFO buffer.

For example , au88x0

according to patent 6167465

Additionally, a first-in-first-out (FIFO) buffer is established for the DMA
channel. Then a DMA request is generated in order to begin filling the FIFO
buffer with data from the first data segment 150(0) using the information
provided by CPU 210.


The FIFO buffer may be any suitable size capable of handling bus latencies
while small enough such that the memory requirement is not overly
burdensome. In one embodiment of the present invention, the FIFO buffer is
32 samples or words in depth, which would withstand a maximum bus latency of
about 4 microseconds. By way of example, if 48 DMA channels trigger
simultaneously, with a trigger level set at half the buffer size (16
samples), each DMA channel can wait 16 samples (20 microseconds per sample),
or approximately 320 microseconds before running out of data.


It seem that alsa-lib should not allow application to rewind the application
pointer to hardware pointer since you cannot write the next sample because
of FIFO buffer even using mmap read/write

or bug in *snd_pcm_rewindable() ?*


2009/9/24 Takashi Iwai <tiwai@suse.de>

> At Thu, 24 Sep 2009 13:04:24 +0530,
> Anuj Aggarwal wrote:
> >
> > Hi,
> >
> > I want to try the forward/rewind APIs supported by the ALSA library.
> > Can someone point to an ALSA application which exercises these APIs?
>
> Pulseaudio is using snd_pcm_rewind().
> About snd_pcm_forward(), I don't know of...
>
>
> Takashi
> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@alsa-project.org
> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
>

Re: Application supporting forward/rewind APIs

[Anuj Aggarwal]

Yeah, I am looking for some sample application to test forward/rewind
functionality.

Regards,
Anuj

On Thu, Sep 24, 2009 at 1:27 PM, Raymond Yau
<superquad.vortex2@gmail.com> wrote:
> Do you mean that there is no test program to verify the implementation is
> correct ?
>
> Some sound card 's hardware has FIFO buffer.
>
> For example , au88x0
>
> according to patent 6167465
>
> Additionally, a first-in-first-out (FIFO) buffer is established for the DMA
> channel. Then a DMA request is generated in order to begin filling the FIFO
> buffer with data from the first data segment 150(0) using the information
> provided by CPU 210.
>
>
> The FIFO buffer may be any suitable size capable of handling bus latencies
> while small enough such that the memory requirement is not overly
> burdensome. In one embodiment of the present invention, the FIFO buffer is
> 32 samples or words in depth, which would withstand a maximum bus latency of
> about 4 microseconds. By way of example, if 48 DMA channels trigger
> simultaneously, with a trigger level set at half the buffer size (16
> samples), each DMA channel can wait 16 samples (20 microseconds per sample),
> or approximately 320 microseconds before running out of data.
>
>
> It seem that alsa-lib should not allow application to rewind the application
> pointer to hardware pointer since you cannot write the next sample because
> of FIFO buffer even using mmap read/write
>
> or bug in *snd_pcm_rewindable() ?*
>
>
> 2009/9/24 Takashi Iwai <tiwai@suse.de>
>
>> At Thu, 24 Sep 2009 13:04:24 +0530,
>> Anuj Aggarwal wrote:
>> >
>> > Hi,
>> >
>> > I want to try the forward/rewind APIs supported by the ALSA library.
>> > Can someone point to an ALSA application which exercises these APIs?
>>
>> Pulseaudio is using snd_pcm_rewind().
>> About snd_pcm_forward(), I don't know of...
>>
>>
>> Takashi
>> _______________________________________________
>> Alsa-devel mailing list
>> Alsa-devel@alsa-project.org
>> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
>>
> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@alsa-project.org
> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
>



-- 
Best Regards,
Anuj Aggarwal

Re: Application supporting forward/rewind APIs

[Raymond Yau]

It seem that the current implementation , it seem that the application can
rewind the application pointer to hardware pointer , rewrite the next
sample.for all drivers


 static snd_pcm_sframes_t snd_pcm_hw_rewindable(snd_pcm_t *pcm)
{
    return snd_pcm_mmap_hw_avail(pcm);
}

However this is almost impossible for any sound cards since the hardware
register just report the number of samples processed. this mean that the
sound card is already processing the next sample.




2009/9/24 Anuj Aggarwal <anuj.aggarwal@gmail.com>

> Yeah, I am looking for some sample application to test forward/rewind
> functionality.
>
> Regards,
> Anuj
>
> On Thu, Sep 24, 2009 at 1:27 PM, Raymond Yau
> <superquad.vortex2@gmail.com> wrote:
> > Do you mean that there is no test program to verify the implementation is
> > correct ?
> >
> > Some sound card 's hardware has FIFO buffer.
> >
> > For example , au88x0
> >
> > according to patent 6167465
> >
> > Additionally, a first-in-first-out (FIFO) buffer is established for the
> DMA
> > channel. Then a DMA request is generated in order to begin filling the
> FIFO
> > buffer with data from the first data segment 150(0) using the information
> > provided by CPU 210.
> >
> >
> > The FIFO buffer may be any suitable size capable of handling bus
> latencies
> > while small enough such that the memory requirement is not overly
> > burdensome. In one embodiment of the present invention, the FIFO buffer
> is
> > 32 samples or words in depth, which would withstand a maximum bus latency
> of
> > about 4 microseconds. By way of example, if 48 DMA channels trigger
> > simultaneously, with a trigger level set at half the buffer size (16
> > samples), each DMA channel can wait 16 samples (20 microseconds per
> sample),
> > or approximately 320 microseconds before running out of data.
> >
> >
> > It seem that alsa-lib should not allow application to rewind the
> application
> > pointer to hardware pointer since you cannot write the next sample
> because
> > of FIFO buffer even using mmap read/write
> >
> > or bug in *snd_pcm_rewindable() ?*
> >
> >
> > 2009/9/24 Takashi Iwai <tiwai@suse.de>
> >
> >> At Thu, 24 Sep 2009 13:04:24 +0530,
> >> Anuj Aggarwal wrote:
> >> >
> >> > Hi,
> >> >
> >> > I want to try the forward/rewind APIs supported by the ALSA library.
> >> > Can someone point to an ALSA application which exercises these APIs?
> >>
> >> Pulseaudio is using snd_pcm_rewind().
> >> About snd_pcm_forward(), I don't know of...
> >>
> >>
> >> Takashi
> >> _______________________________________________
> >> Alsa-devel mailing list
> >> Alsa-devel@alsa-project.org
> >> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
> >>
> > _______________________________________________
> > Alsa-devel mailing list
> > Alsa-devel@alsa-project.org
> > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
> >
>
>
>
> --
> Best Regards,
> Anuj Aggarwal
>

Re: Application supporting forward/rewind APIs

[Anuj Aggarwal]

I found the solution, one can use mplayer to test forward/rewind
feature of ALSA library.

Regards,
Anuj Aggarwal

On Sat, Sep 26, 2009 at 9:29 AM, Raymond Yau
<superquad.vortex2@gmail.com> wrote:
> It seem that the current implementation , it seem that the application can
> rewind the application pointer to hardware pointer , rewrite the next
> sample.for all drivers
>
>
>  static snd_pcm_sframes_t snd_pcm_hw_rewindable(snd_pcm_t *pcm)
> {
>    return snd_pcm_mmap_hw_avail(pcm);
> }
>
> However this is almost impossible for any sound cards since the hardware
> register just report the number of samples processed. this mean that the
> sound card is already processing the next sample.
>
>
>
>
> 2009/9/24 Anuj Aggarwal <anuj.aggarwal@gmail.com>
>
>> Yeah, I am looking for some sample application to test forward/rewind
>> functionality.
>>
>> Regards,
>> Anuj
>>
>> On Thu, Sep 24, 2009 at 1:27 PM, Raymond Yau
>> <superquad.vortex2@gmail.com> wrote:
>> > Do you mean that there is no test program to verify the implementation is
>> > correct ?
>> >
>> > Some sound card 's hardware has FIFO buffer.
>> >
>> > For example , au88x0
>> >
>> > according to patent 6167465
>> >
>> > Additionally, a first-in-first-out (FIFO) buffer is established for the
>> DMA
>> > channel. Then a DMA request is generated in order to begin filling the
>> FIFO
>> > buffer with data from the first data segment 150(0) using the information
>> > provided by CPU 210.
>> >
>> >
>> > The FIFO buffer may be any suitable size capable of handling bus
>> latencies
>> > while small enough such that the memory requirement is not overly
>> > burdensome. In one embodiment of the present invention, the FIFO buffer
>> is
>> > 32 samples or words in depth, which would withstand a maximum bus latency
>> of
>> > about 4 microseconds. By way of example, if 48 DMA channels trigger
>> > simultaneously, with a trigger level set at half the buffer size (16
>> > samples), each DMA channel can wait 16 samples (20 microseconds per
>> sample),
>> > or approximately 320 microseconds before running out of data.
>> >
>> >
>> > It seem that alsa-lib should not allow application to rewind the
>> application
>> > pointer to hardware pointer since you cannot write the next sample
>> because
>> > of FIFO buffer even using mmap read/write
>> >
>> > or bug in *snd_pcm_rewindable() ?*
>> >
>> >
>> > 2009/9/24 Takashi Iwai <tiwai@suse.de>
>> >
>> >> At Thu, 24 Sep 2009 13:04:24 +0530,
>> >> Anuj Aggarwal wrote:
>> >> >
>> >> > Hi,
>> >> >
>> >> > I want to try the forward/rewind APIs supported by the ALSA library.
>> >> > Can someone point to an ALSA application which exercises these APIs?
>> >>
>> >> Pulseaudio is using snd_pcm_rewind().
>> >> About snd_pcm_forward(), I don't know of...
>> >>
>> >>
>> >> Takashi
>> >> _______________________________________________
>> >> Alsa-devel mailing list
>> >> Alsa-devel@alsa-project.org
>> >> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
>> >>
>> > _______________________________________________
>> > Alsa-devel mailing list
>> > Alsa-devel@alsa-project.org
>> > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
>> >
>>
>>
>>
>> --
>> Best Regards,
>> Anuj Aggarwal
>>
> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@alsa-project.org
> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
>



-- 
Best Regards,
Anuj Aggarwal

Re: Application supporting forward/rewind APIs

[Clemens Ladisch]

Anuj Aggarwal wrote:
> I found the solution, one can use mplayer to test forward/rewind
> feature of ALSA library.

mplayer disables ALSA's underrun detection and uses snd_pcm_forward() to
recover from an underrun, if it happens.

(To force an underrun, press Ctrl+S (then Ctrl+Q) to prevent mplayer
from updating its status line.)


HTH
Clemens

Re: Application supporting forward/rewind APIs

[Raymond Yau]

Do you mean that the application can use snd_pcm_rewind() to rewind the
application pointer to hardware pointer and rewrite the next sample ( behind
the hardware pointer ) for usb audio driver ? ( real time mixing like
pulseaudio )



2009/9/29 Clemens Ladisch <clemens@ladisch.de>

> Anuj Aggarwal wrote:
> > I found the solution, one can use mplayer to test forward/rewind
> > feature of ALSA library.
>
> mplayer disables ALSA's underrun detection and uses snd_pcm_forward() to
> recover from an underrun, if it happens.
>
> (To force an underrun, press Ctrl+S (then Ctrl+Q) to prevent mplayer
> from updating its status line.)
>
>
> HTH
> Clemens
>

Re: Application supporting forward/rewind APIs

[Raymond Yau]

It seem that the difference between the application pointer and the hardware
pointer is just the theoretical value which none of the sound card can
achieve


static snd_pcm_sframes_t snd_pcm_hw_rewindable(snd_pcm_t *pcm)
{
    return snd_pcm_mmap_hw_avail(pcm);
}

To allow the application rewind the application pointer to hardware pointer
and rewrite the next sample immediately at any time

The audio controller have to fetch the audio data as the same rate as the
sampling rate.

The practical value may be the difference between the application pointer
and the nearest period boundary


2009/9/24 Takashi Iwai <tiwai@suse.de>

> At Thu, 24 Sep 2009 13:04:24 +0530,
> Anuj Aggarwal wrote:
> >
> > Hi,
> >
> > I want to try the forward/rewind APIs supported by the ALSA library.
> > Can someone point to an ALSA application which exercises these APIs?
>
> Pulseaudio is using snd_pcm_rewind().
> About snd_pcm_forward(), I don't know of...
>
>
> Takashi
> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@alsa-project.org
> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
>