PCM application question: readn

PCM application question: readn

[Bruce Paterson]

Hi alsa people,

OK, this is probably in the dumb green user category of question but we
are all there at some
time or other !  Nothing in the archives seems to help.

Background:
I am writing a simple linux application which uses a professional
multichannel soundcard: envy24
Originally parts of this program were done under windows, but things
were getting real messy with
the standard windows API when you need more than 2 channels capture.
Alsa 0.9 seems to fit the
bill perfectly, allowing 96000 sample rate on 4 channels with 24 bit
sampling, and even in & out
sync ! 

Where I'm at:
alsa 0.9.0rc2 has been installed sucessfully. aplay works, evny24control
(wonderful!!) works.
Also, if I only playback from my application, it works (as long as I use
plughw:0.0)

Problem 1:
When I try to record I get segmentation fault in
"snd_pcm_route_convert1_one" called indirectly
by my "snd_pcm_readn" call. I would prefer to use readn rather than
readi since it suits my
application better. The capture is opened in blocking mode (whereas my
playback was opened in
non-blocking mode). 
It is possible I have misinterpreted the parameters for "snd_pcm_readn",
but the API doco doesn't
describe "void **bufs" very well. I have assumed I am meant to pass a
pointer to an array of
pointers (array size = #channels configured), which in turn point to
buffers (one for each channel)
each which must be at least as big as ("size" *
#bytes-needed-to-store-sample) bytes. In this current
test I am using 16bit samples, but I'm using the "snd_pcm_format_width"
anyway. I have assumed the
buffers for the channels do not need to be contigueous with each other.
Is this correct ?

Problem 2:
When I try device "hw:0.0" the very first hardware parameter set fails
with unavailable. It's
 snd_pcm_hw_params_set_access(handle, params,
SND_PCM_ACCESS_RW_NONINTERLEAVED); that fails.
I have seen other posts talking about using non-interleaved frames....
surely the ice1712
supports this ??


-- 
Cheers,
Bruce
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Re: PCM application question: readn

[Jaroslav Kysela]

On Wed, 3 Jul 2002, Bruce Paterson wrote:

> 
> Hi alsa people,
> 
> OK, this is probably in the dumb green user category of question but we
> are all there at some
> time or other !  Nothing in the archives seems to help.
> 
> Background:
> I am writing a simple linux application which uses a professional
> multichannel soundcard: envy24
> Originally parts of this program were done under windows, but things
> were getting real messy with
> the standard windows API when you need more than 2 channels capture.
> Alsa 0.9 seems to fit the
> bill perfectly, allowing 96000 sample rate on 4 channels with 24 bit
> sampling, and even in & out
> sync ! 
> 
> Where I'm at:
> alsa 0.9.0rc2 has been installed sucessfully. aplay works, evny24control
> (wonderful!!) works.
> Also, if I only playback from my application, it works (as long as I use
> plughw:0.0)
> 
> Problem 1:
> When I try to record I get segmentation fault in
> "snd_pcm_route_convert1_one" called indirectly
> by my "snd_pcm_readn" call. I would prefer to use readn rather than
> readi since it suits my
> application better. The capture is opened in blocking mode (whereas my
> playback was opened in
> non-blocking mode). 
> It is possible I have misinterpreted the parameters for "snd_pcm_readn",
> but the API doco doesn't
> describe "void **bufs" very well. I have assumed I am meant to pass a
> pointer to an array of
> pointers (array size = #channels configured), which in turn point to
> buffers (one for each channel)
> each which must be at least as big as ("size" *
> #bytes-needed-to-store-sample) bytes. In this current
> test I am using 16bit samples, but I'm using the "snd_pcm_format_width"
> anyway. I have assumed the
> buffers for the channels do not need to be contigueous with each other.
> Is this correct ?
> 
> Problem 2:
> When I try device "hw:0.0" the very first hardware parameter set fails
> with unavailable. It's
>  snd_pcm_hw_params_set_access(handle, params,
> SND_PCM_ACCESS_RW_NONINTERLEAVED); that fails.
> I have seen other posts talking about using non-interleaved frames....
> surely the ice1712
> supports this ??

Not in hardware. Non-interleaved access is emulated. Anyway, if you send 
me a short code showing the problem, I'll try to fix the problem.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project  http://www.alsa-project.org
SuSE Linux    http://www.suse.com



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