[arch-general] Opinions on pulseaudio [WAS: PulseAudio in [testing]]

[fons at kokkinizita.net]

On Mon, Nov 29, 2010 at 07:28:45AM +0800, Ng Oon-Ee wrote:

> The ONLY major ALSA 'feature' which is not supported is memmap. Direct
> access to the sound-card's memory. Pulseaudio's devs are of the opinion
> that this cannot and should not be emulated, and that apps which use it
> are broken in design. I've not come across any latest-version-apps where
> this is still a problem, do you know of any?

While I would agree with anything else you wrote, if the comment
quoted above refers to ALSA's mmap access mode it is wrong.

All this mode has to do is provide the client application with 
pointers to read/write a period of samples from/to. The memory
pointed to _may_ be directly mapped to a HW buffer, but there
is nothing in the API that requires this - it could just be a
user space memory buffer. ALSA itself provides mmap access to
e.g. USB audio devices, this most certainly does not provide
pointers to any USB hardware.

Mmap mode can be emulated quite easily on top of another access
mode (although it usually makes more sense to do things the other
way round). 

There is nothing wrong with apps using this mode, and in fact
many do, including Jack. Given that any driver will have either
access to real HW buffers, or will create its own ones in memory,
it's in fact the simplest and most direct way to get to the audio
data.

Ciao,

-- 
FA

There are three of them, and Alleline.