Re: [LAU] RTC/HPET timer permissions

Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]
To: <linux-audio-user@...>
Date: Sunday, November 25, 2012 - 2:32 pm

On Sunday 25 November 2012 08:44:57 Clemens Ladisch did opine:

> Brent Busby wrote:

Chuckle. You are worried about an 8 kilohertz IRQ?

I have an app on this machine that uses about a 25khz IRQ, Actually slow
because this quad core phenom at 2.1Ghz, has lousy latency test figures,
and were this machine better suited, the app could ask for 50 kilohertz or
better.

It is however, tied to this kernel version:

2.6.32-122-rtai

Because RTAI, when enabled, actually becomes the top dog to do that, with
the kernel playing 2nd fiddle, all other apps get what time is left over.

But everything else on this machine still continues to function albeit at a
slightly slower speed. So it is actually running right now as I type this.

The reason for its existence on this machine is that I do have 2 machines
out in the shop that are suitable for running at a 40+ kilohertz loop rate,
my lathe and my desktop milling machine are both running this same install.
They are running it on Intel "atom" D525MW boards with 2Gb of dram. On that
board, absolute worst case latency is 7 microseconds that might occur while
opening something like firefox. Normal runs 2 to 3. Microseconds. Great
mobo for us, very low power and dirt cheap. But no expansion facilities to
plug in any fancy sound cards. But it does have decent onboard video and
sound, but I haven't tested the sound, it would be hard to hear well when a
6 pack of nema 23 sized double and triple stack stepper motors are growling
as they go about their work, carving steel to thousandth of an inch
accuracies.

FWIW, if I have any xruns or stutters in the sound here, its generally
because my net connection is only a 3 megabit from cable & that can get a
bit stuttery of an evening when the cable folks big pipe gets loaded up.
It not a big enough problem to make me yell at the cable folks.

Point is, low latency CAN be done. On 260 USD machines that are ready to
run OOTB. 250Gb SATA hard drive, and an optical dvd writer/reader.

But now I am curious. The cd to install this is available from

I'd be interested in finding out if this approach would do you folks any
good with your latency related problems.

Cheers, Gene
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
My web page: is up!
Think twice before speaking, but don't say "think think click click".
_______________________________________________
Linux-audio-user mailing list
Linux-audio-user@lists.linuxaudio.org
http://lists.linuxaudio.org/listinfo/linux-audio-user

Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]

Messages in current thread:
[LAU] RTC/HPET timer permissions, Brent Busby, (Sun Nov 25, 10:00 am)
Re: [LAU] RTC/HPET timer permissions, Clemens Ladisch, (Sun Nov 25, 12:23 pm)
Re: [LAU] RTC/HPET timer permissions, Jeremy Jongepier, (Sun Nov 25, 8:17 pm)
Re: [LAU] RTC/HPET timer permissions, Clemens Ladisch, (Mon Nov 26, 2:03 pm)
Re: [LAU] RTC/HPET timer permissions, Robert Jonsson, (Tue Nov 27, 11:10 am)
Re: [LAU] RTC/HPET timer permissions, Jeremy Jongepier, (Tue Nov 27, 10:41 am)
Re: [LAU] RTC/HPET timer permissions, Clemens Ladisch, (Tue Nov 27, 12:32 pm)
Re: [LAU] RTC/HPET timer permissions, Ralf Mardorf, (Tue Nov 27, 11:39 am)
Re: [LAU] RTC/HPET timer permissions, Jeremy Jongepier, (Tue Nov 27, 11:55 am)
Re: [LAU] RTC/HPET timer permissions, Brent Busby, (Mon Nov 26, 3:24 pm)
Re: [LAU] RTC/HPET timer permissions, Clemens Ladisch, (Mon Nov 26, 3:26 pm)
Re: [LAU] RTC/HPET timer permissions, Brent Busby, (Sun Nov 25, 7:05 pm)
Re: [LAU] RTC/HPET timer permissions, Gene Heskett, (Sun Nov 25, 2:32 pm)