ALSA snd_xferi_t buffer arrangment

ALSA snd_xferi_t buffer arrangment

[Assaf Hoffman]

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Hi,

I'm mew to sound and ALSA.

My project deals with PCM in standard (I2S) mode and IEC958 (SPDIF)
mode. 

Can anyone tell me how the ALSA stack expects to "see" the data received
form the sound device? I mean, what is the format of the data DMA'ed
from the sound device to DRAM that the ALSA stack expects? 

Is this raw sound data? SPDIF frame includes non sound data as well.
Does the sound card HW strip the sound payload from the IEC958 frame to
deliver the raw sound data to the ALSA buffer? 

Please shed some light...

Many thanks. 

 

 

 

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Assaf Hoffman - Senior SW engineer
Marvell Semiconductor Israel Ltd
6 Hamada Street 
Mordot HaCarmel Industrial Park
Yokneam 20692, ISRAEL
Email - hoffman@marvell.com
Tel - + 972 4 9091203 
Fax - + 972 4 9091565
WWW Page: http://www.marvell.com 

This message may contain confidential, proprietary or legally privileged
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Re: ALSA snd_xferi_t buffer arrangment

[James Courtier-Dutton]

Assaf Hoffman wrote:
> Hi,
> 
> I'm mew to sound and ALSA.
> 
> My project deals with PCM in standard (I2S) mode and IEC958 (SPDIF)
> mode. 
> 
> Can anyone tell me how the ALSA stack expects to "see" the data received
> form the sound device? I mean, what is the format of the data DMA'ed
> from the sound device to DRAM that the ALSA stack expects? 
> 
> Is this raw sound data? SPDIF frame includes non sound data as well.
> Does the sound card HW strip the sound payload from the IEC958 frame to
> deliver the raw sound data to the ALSA buffer? 
> 
> Please shed some light...
> 
> Many thanks. 
> 
>  

ALSA can deal with all the different formats that the sound device might
deliver. The low level sound driver simply tells the upper layers what
formats are available. ALSA then handles those formats and all format
conversion required to reach the user space application.
It depends what your device does as to which format ALSA will see.

James





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Re: ALSA snd_xferi_t buffer arrangment

[Assaf Hoffman]

Thank you for your reply.
Please let me clarify. What you say is that my device can deliver a raw
ICE958 data from the capture channel to the DMA buffer and the ALSA
stack will know how to deal with it? No need for the device to strip
down the payload and only then transfer it to the DMA buffer?
In case the sound card can strip down the IEC958 frames into raw sound
data + ch status + user data, how would the ALSA stack expect the data?
Is there an API for that?
Thanks again.


-----Original Message-----
From: James Courtier-Dutton [mailto:James@superbug.co.uk] 
Sent: Wednesday, October 11, 2006 3:54 PM
To: Assaf Hoffman
Cc: alsa-devel@lists.sourceforge.net; Rita Shtern
Subject: Re: [Alsa-devel] ALSA snd_xferi_t buffer arrangment

Assaf Hoffman wrote:
> Hi,
> 
> I'm mew to sound and ALSA.
> 
> My project deals with PCM in standard (I2S) mode and IEC958 (SPDIF)
> mode. 
> 
> Can anyone tell me how the ALSA stack expects to "see" the data
received
> form the sound device? I mean, what is the format of the data DMA'ed
> from the sound device to DRAM that the ALSA stack expects? 
> 
> Is this raw sound data? SPDIF frame includes non sound data as well.
> Does the sound card HW strip the sound payload from the IEC958 frame
to
> deliver the raw sound data to the ALSA buffer? 
> 
> Please shed some light...
> 
> Many thanks. 
> 
>  

ALSA can deal with all the different formats that the sound device might
deliver. The low level sound driver simply tells the upper layers what
formats are available. ALSA then handles those formats and all format
conversion required to reach the user space application.
It depends what your device does as to which format ALSA will see.

James





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Re: ALSA snd_xferi_t buffer arrangment

[James Courtier-Dutton]

Assaf Hoffman wrote:
> Thank you for your reply.
> Please let me clarify. What you say is that my device can deliver a raw
> ICE958 data from the capture channel to the DMA buffer and the ALSA
> stack will know how to deal with it? No need for the device to strip
> down the payload and only then transfer it to the DMA buffer?
> In case the sound card can strip down the IEC958 frames into raw sound
> data + ch status + user data, how would the ALSA stack expect the data?
> Is there an API for that?
> Thanks again.
> 

If you don't strip the IEC958 frames, tell ALSA the format is:
SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_LE
SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_BE
If you do strip the IEC958 frames, tell ALSA the format is:
SNDRV_PCM_FMTBIT_S24_LE or
SNDRV_PCM_FMTBIT_S16_LE

Or whatever format your hardware decides to send.

The API for this is contained in the following structure in the sound
driver:
This example is from the snd-emu10k1 driver.

static struct snd_pcm_hardware snd_emu10k1_capture =
{
        .info =                 (SNDRV_PCM_INFO_MMAP |
SNDRV_PCM_INFO_INTERLEAVED |
                                 SNDRV_PCM_INFO_BLOCK_TRANSFER |
                                 SNDRV_PCM_INFO_RESUME |
                                 SNDRV_PCM_INFO_MMAP_VALID),
        .formats =              SNDRV_PCM_FMTBIT_S16_LE,
        .rates =                SNDRV_PCM_RATE_8000_48000,
        .rate_min =             8000,
        .rate_max =             48000,
        .channels_min =         1,
        .channels_max =         2,
        .buffer_bytes_max =     (64*1024),
        .period_bytes_min =     384,
        .period_bytes_max =     (64*1024),
        .periods_min =          2,
        .periods_max =          2,
        .fifo_size =            0,
};


As you can see, it tells use that this device can do only
SNDRV_PCM_FMTBIT_S16_LE format.

James


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Re: ALSA snd_xferi_t buffer arrangment

[Assaf Hoffman]

Hi,
Thanks again for clear answers.
In case the HW strip the IEC958 frames, where the ALSA stack expect to
find the various frame data fields such as perr, valid bit, audio
sample, user data and channel status? Is there a data structure the HW
should follow when DMAing the striped data to the DRAM buffer?
What do you think of such acceleration? Does this saves a significant
CPU time processing the ICE958 frames?
Many thanks.
P.S.
I was looking into the ASLA stack and I could find
SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_XX only in snd_pcm_hardware structure
initialization. I could not see where it is used to tell the ALSA to
process the data as IEC958 frames.


-----Original Message-----
From: James Courtier-Dutton [mailto:James@superbug.co.uk] 
Sent: Wednesday, October 11, 2006 4:23 PM
To: Assaf Hoffman
Cc: alsa-devel@lists.sourceforge.net; Rita Shtern
Subject: Re: [Alsa-devel] ALSA snd_xferi_t buffer arrangment

Assaf Hoffman wrote:
> Thank you for your reply.
> Please let me clarify. What you say is that my device can deliver a
raw
> ICE958 data from the capture channel to the DMA buffer and the ALSA
> stack will know how to deal with it? No need for the device to strip
> down the payload and only then transfer it to the DMA buffer?
> In case the sound card can strip down the IEC958 frames into raw sound
> data + ch status + user data, how would the ALSA stack expect the
data?
> Is there an API for that?
> Thanks again.
> 

If you don't strip the IEC958 frames, tell ALSA the format is:
SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_LE
SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_BE
If you do strip the IEC958 frames, tell ALSA the format is:
SNDRV_PCM_FMTBIT_S24_LE or
SNDRV_PCM_FMTBIT_S16_LE

Or whatever format your hardware decides to send.

The API for this is contained in the following structure in the sound
driver:
This example is from the snd-emu10k1 driver.

static struct snd_pcm_hardware snd_emu10k1_capture =
{
        .info =                 (SNDRV_PCM_INFO_MMAP |
SNDRV_PCM_INFO_INTERLEAVED |
                                 SNDRV_PCM_INFO_BLOCK_TRANSFER |
                                 SNDRV_PCM_INFO_RESUME |
                                 SNDRV_PCM_INFO_MMAP_VALID),
        .formats =              SNDRV_PCM_FMTBIT_S16_LE,
        .rates =                SNDRV_PCM_RATE_8000_48000,
        .rate_min =             8000,
        .rate_max =             48000,
        .channels_min =         1,
        .channels_max =         2,
        .buffer_bytes_max =     (64*1024),
        .period_bytes_min =     384,
        .period_bytes_max =     (64*1024),
        .periods_min =          2,
        .periods_max =          2,
        .fifo_size =            0,
};


As you can see, it tells use that this device can do only
SNDRV_PCM_FMTBIT_S16_LE format.

James


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Re: ALSA snd_xferi_t buffer arrangment

[James Courtier-Dutton]

Assaf Hoffman wrote:
> Hi,
> Thanks again for clear answers.
> In case the HW strip the IEC958 frames, where the ALSA stack expect to
> find the various frame data fields such as perr, valid bit, audio
> sample, user data and channel status? Is there a data structure the HW
> should follow when DMAing the striped data to the DRAM buffer?
> What do you think of such acceleration? Does this saves a significant
> CPU time processing the ICE958 frames?
> Many thanks.
> P.S.
> I was looking into the ASLA stack and I could find
> SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_XX only in snd_pcm_hardware structure
> initialization. I could not see where it is used to tell the ALSA to
> process the data as IEC958 frames.
> 

A majority of sound cards strip the frame, and only put the audio
samples in the DMA buffer. The sound card then stores the valid bits,
non-audio bit, user data etc. in a separate register on the sound card.

The processing of the IEC958 frames is done in alsa-lib.
ALSA has two parts, and kernel part, and a user space lib.
The kernel part does as little as possible, with the user space part
doing all the format conversion etc.

I have not looked closely, but I don't know if the alsa-lib decodes the
IEC958 frames or not yet.

James




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Re: ALSA snd_xferi_t buffer arrangment

[Takashi Iwai]

At Wed, 11 Oct 2006 16:00:54 +0100,
James Courtier-Dutton wrote:
> 
> Assaf Hoffman wrote:
> > Hi,
> > Thanks again for clear answers.
> > In case the HW strip the IEC958 frames, where the ALSA stack expect to
> > find the various frame data fields such as perr, valid bit, audio
> > sample, user data and channel status? Is there a data structure the HW
> > should follow when DMAing the striped data to the DRAM buffer?
> > What do you think of such acceleration? Does this saves a significant
> > CPU time processing the ICE958 frames?
> > Many thanks.
> > P.S.
> > I was looking into the ASLA stack and I could find
> > SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_XX only in snd_pcm_hardware structure
> > initialization. I could not see where it is used to tell the ALSA to
> > process the data as IEC958 frames.
> > 
> 
> A majority of sound cards strip the frame, and only put the audio
> samples in the DMA buffer. The sound card then stores the valid bits,
> non-audio bit, user data etc. in a separate register on the sound card.
> 
> The processing of the IEC958 frames is done in alsa-lib.
> ALSA has two parts, and kernel part, and a user space lib.
> The kernel part does as little as possible, with the user space part
> doing all the format conversion etc.
> 
> I have not looked closely, but I don't know if the alsa-lib decodes the
> IEC958 frames or not yet.

It can.  iec958 plugin does encode/decode IEC958 frames.


Takashi

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Re: ALSA snd_xferi_t buffer arrangment

[James Courtier-Dutton]

Takashi Iwai wrote:
> At Wed, 11 Oct 2006 16:00:54 +0100,
> James Courtier-Dutton wrote:
>> Assaf Hoffman wrote:
>>> Hi,
>>> Thanks again for clear answers.
>>> In case the HW strip the IEC958 frames, where the ALSA stack expect to
>>> find the various frame data fields such as perr, valid bit, audio
>>> sample, user data and channel status? Is there a data structure the HW
>>> should follow when DMAing the striped data to the DRAM buffer?
>>> What do you think of such acceleration? Does this saves a significant
>>> CPU time processing the ICE958 frames?
>>> Many thanks.
>>> P.S.
>>> I was looking into the ASLA stack and I could find
>>> SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_XX only in snd_pcm_hardware structure
>>> initialization. I could not see where it is used to tell the ALSA to
>>> process the data as IEC958 frames.
>>>
>> A majority of sound cards strip the frame, and only put the audio
>> samples in the DMA buffer. The sound card then stores the valid bits,
>> non-audio bit, user data etc. in a separate register on the sound card.
>>
>> The processing of the IEC958 frames is done in alsa-lib.
>> ALSA has two parts, and kernel part, and a user space lib.
>> The kernel part does as little as possible, with the user space part
>> doing all the format conversion etc.
>>
>> I have not looked closely, but I don't know if the alsa-lib decodes the
>> IEC958 frames or not yet.
> 
> It can.  iec958 plugin does encode/decode IEC958 frames.
> 
> 
> Takashi

Does it let the user app set the valid, non-audio etc. bits?


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Re: ALSA snd_xferi_t buffer arrangment

[Takashi Iwai]

At Wed, 11 Oct 2006 16:19:44 +0100,
James Courtier-Dutton wrote:
> 
> Takashi Iwai wrote:
> > At Wed, 11 Oct 2006 16:00:54 +0100,
> > James Courtier-Dutton wrote:
> >> Assaf Hoffman wrote:
> >>> Hi,
> >>> Thanks again for clear answers.
> >>> In case the HW strip the IEC958 frames, where the ALSA stack expect to
> >>> find the various frame data fields such as perr, valid bit, audio
> >>> sample, user data and channel status? Is there a data structure the HW
> >>> should follow when DMAing the striped data to the DRAM buffer?
> >>> What do you think of such acceleration? Does this saves a significant
> >>> CPU time processing the ICE958 frames?
> >>> Many thanks.
> >>> P.S.
> >>> I was looking into the ASLA stack and I could find
> >>> SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_XX only in snd_pcm_hardware structure
> >>> initialization. I could not see where it is used to tell the ALSA to
> >>> process the data as IEC958 frames.
> >>>
> >> A majority of sound cards strip the frame, and only put the audio
> >> samples in the DMA buffer. The sound card then stores the valid bits,
> >> non-audio bit, user data etc. in a separate register on the sound card.
> >>
> >> The processing of the IEC958 frames is done in alsa-lib.
> >> ALSA has two parts, and kernel part, and a user space lib.
> >> The kernel part does as little as possible, with the user space part
> >> doing all the format conversion etc.
> >>
> >> I have not looked closely, but I don't know if the alsa-lib decodes the
> >> IEC958 frames or not yet.
> > 
> > It can.  iec958 plugin does encode/decode IEC958 frames.
> > 
> > 
> > Takashi
> 
> Does it let the user app set the valid, non-audio etc. bits?

Yes, it takes arguments.


Takashi

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Re: ALSA snd_xferi_t buffer arrangment

[Assaf Hoffman]

Hi,
Thank you for your reply.
I would be happy if you kindly reply to the following questions:
1) According to your experience, is it correct to assume that once a PCM

   instance for playback/capture is prepared and triggered, the user
data 
   and channel status are constants during data transmit/receive?
2) In the case HW saves the user data and channel status in its internal

   registers, how would the ALSA stack know of any of them changed?
3) Is there a bridge application in the ALSA stack (kerne)? I mean, in
case 
   I would like to capture ICE958 frames and route them to ICE958
playback 
   channel.

Thanks.

-----Original Message-----
From: James Courtier-Dutton [mailto:James@superbug.co.uk] 
Sent: Wednesday, October 11, 2006 5:01 PM
To: Assaf Hoffman
Cc: alsa-devel@lists.sourceforge.net; Rita Shtern
Subject: Re: [Alsa-devel] ALSA snd_xferi_t buffer arrangment

Assaf Hoffman wrote:
> Hi,
> Thanks again for clear answers.
> In case the HW strip the IEC958 frames, where the ALSA stack expect to
> find the various frame data fields such as perr, valid bit, audio
> sample, user data and channel status? Is there a data structure the HW
> should follow when DMAing the striped data to the DRAM buffer?
> What do you think of such acceleration? Does this saves a significant
> CPU time processing the ICE958 frames?
> Many thanks.
> P.S.
> I was looking into the ASLA stack and I could find
> SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_XX only in snd_pcm_hardware structure
> initialization. I could not see where it is used to tell the ALSA to
> process the data as IEC958 frames.
> 

A majority of sound cards strip the frame, and only put the audio
samples in the DMA buffer. The sound card then stores the valid bits,
non-audio bit, user data etc. in a separate register on the sound card.

The processing of the IEC958 frames is done in alsa-lib.
ALSA has two parts, and kernel part, and a user space lib.
The kernel part does as little as possible, with the user space part
doing all the format conversion etc.

I have not looked closely, but I don't know if the alsa-lib decodes the
IEC958 frames or not yet.

James




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Re: ALSA snd_xferi_t buffer arrangment

[Assaf Hoffman]

Hi,
The ALSA PCM supported formats are located in pcm.h file. 
Where can I find the specification (bit fields) of those PCM formats?
Many thanks.


-----Original Message-----
From: James Courtier-Dutton [mailto:James@superbug.co.uk] 
Sent: Wednesday, October 11, 2006 3:54 PM
To: Assaf Hoffman
Cc: alsa-devel@lists.sourceforge.net; Rita Shtern
Subject: Re: [Alsa-devel] ALSA snd_xferi_t buffer arrangment

Assaf Hoffman wrote:
> Hi,
> 
> I'm mew to sound and ALSA.
> 
> My project deals with PCM in standard (I2S) mode and IEC958 (SPDIF)
> mode. 
> 
> Can anyone tell me how the ALSA stack expects to "see" the data
received
> form the sound device? I mean, what is the format of the data DMA'ed
> from the sound device to DRAM that the ALSA stack expects? 
> 
> Is this raw sound data? SPDIF frame includes non sound data as well.
> Does the sound card HW strip the sound payload from the IEC958 frame
to
> deliver the raw sound data to the ALSA buffer? 
> 
> Please shed some light...
> 
> Many thanks. 
> 
>  

ALSA can deal with all the different formats that the sound device might
deliver. The low level sound driver simply tells the upper layers what
formats are available. ALSA then handles those formats and all format
conversion required to reach the user space application.
It depends what your device does as to which format ALSA will see.

James





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