linuxaudio.org

On Sunday 25 November 2012 08:44:57 Clemens Ladisch did opine:
> Brent Busby wrote:

quoted text
> > Is it still necessary or recommended these days for proper operation

> > of audio apps to have a user-accessible /dev/rtc?

>

> Not really.  Using the RTC or HPET devices directly is necessary only if

> the kernel does not use them for timers.  Nowadays, kernels do, and

> applications use the proper timer APIs.

>

> You'd need this only if you're using some audio application that hasn't

> been updated for many years.

>

> > Is there a security risk?

>

> The risk was that handling interrupts at a frequency of 8 kHz would not

> leave enough CPU time for applications.  I doubt that you have any CPU

> where this is actually the case.

>

>

> Regards,

> Clemens

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

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