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: Joshua Haberman (joshua_AT_haberman.com)
Date: Mon Jul 15 2002 - 22:48:13 EEST


* Paul Davis (pbd_AT_op.net) wrote:
> >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.
>
> forget all this and use snd_pcm_mmap_copy_areas.

Huh?

$ grep snd_pcm_mmap_copy_areas /usr/include/alsa/*
$

Josh


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