Re: [linux-audio-dev] Exact description of PCM system for ALSA

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Subject: Re: [linux-audio-dev] Exact description of PCM system for ALSA
From: joy (joy_AT_pingfm.org)
Date: Mon Jul 15 2002 - 15:42:30 EEST


On Wed, Jul 10, 2002 at 10:22:33AM -0700, Joshua Haberman wrote:
> * Philipp Vollmer (vollmer.philipp_AT_t-online.de) wrote:
> > Hello list,
> >
> > I'm searching for a exact description of the PCM system.
> > The ALSA examples and HOWTO give a rough description of this system.
> > I actually only want to understand this system and want to create some
> > little application creating sine or other signals. There are some complex
> > signal generator examples online, but no simple description. Are there
> > books, really good examples or tutorials about this?
>
> It's a rough work-in-progress, but I have an overview of ALSA in the
> works:
>
> http://people.debian.org/~joshua/t1.html
>
hi,

as i said above, nice work, and nice that someone does this.
i tried yesterday your mmap implemantation and at least get it to work
somehow, but im right that:

outbuffer = (area->addr + (area->first + area->step * (offset)) / 8);

returns only a pointer to the buffer? i have to do:

          memset(outbuffer, 0, frames_transmit);
          memcpy(outbuffer, data, frames_transmit);

to really wright data to the buffer. i get also some kind of fragments
staying in buffer if i guess one 'frames_transmit' is smaller than the
written before or/and if its not aligned to fragment_size, a funny
effect, but im currently don't know how to clean it up.

-- 
regards

____- joy

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