Subject: [linux-audio-dev] 1.5 ms latency possible?
From: Anders Torger (torger_AT_ludd.luth.se)
Date: Tue Dec 31 2002 - 20:53:46 EET
I have made a program which is to be run on a dedicated computer,
equipped only with a multichannel soundcard (hammerfall), a small LCD
and a remote control. This forms a dedicated surround processor (if
interested in the software, look at
http://www.ludd.luth.se/users/torger/almusvcu.html) for use in
multichannel HiFi systems.
In some configurations, a 64 sample processing block is relevant,
leaving a total IO-delay of 128 samples, which in 44.1 kHz is about 3
ms.
With such a configuration, I have got the system going for a few hours
at most before underflow. Of course the relevant processes are realtime
scheduled, I have even used tricks with sched_yield to get the
processes yield in the right order (I will probably have to pay for
that sooner or later though) for the most safe operation.
So, my question to this list is if someone has run a similar system for
days without underflows, and if there is some guide or tips on how to
put together the for the moment best low-latency kernel, if there are
kernel features that should be avoided, some bad driver or filesystem
perhaps, and if there are some hardware setting tricks (apart from
giving the sound card the highest interrupt priority). Perhaps tips on
which user space processes that should not run (I have no syslogd or
cron, but sshd is running)
Is it even possible today to build an embedded system with 1.5 ms
processing block based on Linux, which runs until hardware or power
failure? Oh, my software does not necessarily need to access any
filesystem while it is processing, although it would be good if it
could (to continuously save volume settings and similar if changed
through the remote control). So it can be seen as a strict
soundcard-to-the-cpu-and-back problem.
/Anders Torger
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