On Fri, 10 Oct 2003, Paul Davis wrote:
> >I mentioned my ham radio realtime program with mmap
> >in a posting on 3. Oct and before.
> >It works now with ALSA 0.9.7 with AC97 and maybe some other cards, thanks!!!
> >With ESS ES1969 mmap(ibuf, isize, PROT_READ, MAP_FILE | MAP_SHARED |
> >MAP_FIXED, fd_audio, 0)
> >(and I tried also all other MAP_ options) it breaks with I / O error.
> >Do You know some help about mmap besides man,
>
> IIRC, mmap with OSS doesn't work unless you use the LD_PRELOAD
> hack. this loads a library that intercepts all standard system calls
> and routes them through alsa-lib. your app will not run without
> this. why? mmap provides direct access to the DMA buffer of the
> hardware, and thus bypasses most of what alsa-lib does. ALSA does
> support such direct access, but not in the simplistic way that OSS
> provides.
>
> or can I do something with "Scatter Gather" in ALSA API,
> >or does it help if i work myself into JACK for this problem?
> >hints welcome, tnx!!!
>
> either use ALSA natively, or use JACK, or use the LD_PRELOAD hack.
Fully agree. Just to clarify: In-kernel OSS's mmap can be used when
the soundcard's DMA buffer has exactly same parameters as
application requested. We cannot do any automatic conversions
like in the read()/write() case.
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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