Re: real-time threaded IO with low latency (audio)

est@hyperreal.org
Sun, 18 Jul 1999 16:47:02 -0700 (PDT)

Benno Senoner <sbenno@gardena.net> discourseth:
> David Olofson is developing an audio driver system for Linux
> which uses RT-Linux and an API which will fit well into the actual
> sound driver API. The goal will be a driver concept ,
> adapting OSS/Free or ALSA to allow RTLinux tasks to access the
> sound drivers, and providing HARD REALTIME priority.
> With such a system we will able to archieve <1-2ms latency,
> close to the hardware limits of the soundcard, and without audio dropouts
> even on the highest system load ( disk I/O , gfx etc.) , because
> the entire Linux runs at the lowest priority. and is fully preemptable
> by the RT Linux tasks.
> It seems that RT Linux will go in to the main kernel thread with 2.4,
> and for reliable very low-lantency audio ( <5ms) , RTLinux seems the
> best way to go.

Benno,

Having looked at the RT-Linux documentation, my impression was that
its task programming environment was even more restrictive than that
for regular device drivers. That doesn't sound like a platform that
will produce interesting audio applications.

My current understanding is that acheiving our audio latency goals
depends on two things at the moment:

1) Less locking in the kernel. I understand that this is slowly
coming about, but I'd like to be able to better track what can be
expected when. Measuring where things are *now* is aided by programs
such as your latencytest.

2) HZ > 100. This is so we can have something other than monolithic
programs that open and get their timing from the soundcard.
Apparently, this is easy to do now, but I wonder when it will
mainstream and be available in some distributions.

Best of Real-Time,

Eric

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