[LAU] OS for realtime operation

[gene heskett]

On Tuesday, January 10, 2012 09:28:12 AM Jeremy Jongepier did opine:

> On 01/10/12 01:07, Diego Simak wrote:
> > If that kernel is not suitable for you (I mean, you get a lot of
> > xruns), then you can use the PREEMPT or RT Kernels that are included
> > in the Official Ubuntu Repositories (which are configured in the apt
> > sources automatically) and see how it works before going to a manual
> > kernel compillation.
> 
> 10.04 does have a real-time kernel in the repos, 2.6.31-rt.

This isn't exactly realtime, where latencies measured in small numbers of 
microseconds count big time.  Over on the emc list, where we depend on 
being able to feed stepper motors with very steady heartbeats to keep them 
running smoothly at high speeds, we have found a motherboard with extremely 
low latencies, like 7 microseconds without resorting to the use of the 
isolcpus= boot param, and with it, figures in the 5 microsecond range have 
been seen.

This is on a dirt cheap intel D-525 motherboard, with a dual core 1.8 ghz 
atom cpu on it, doesn't even need a fan!  I just bought the whole box with 
2Gb of ram, a 250Gb Sata HD and a sata dvd writer for $246 delivered to my 
front deck.

Because emc is a special build, running only on an RTAI enabled kernel, we 
are stuck with a 2.6.32 kernel that comes with ubuntu-10.04 LTS, but I just 
saw where next LTS is already committed to a 3.2 kernel.

> But the
> 2.6.33 real-time kernel from Tango Studio is superior. At least, I
> didn't have a lot of success with the real-time kernel from the Ubuntu
> repos while the one from Tango Studios is still going strong.
> Later versions of Ubuntu do not have a real-time kernel available
> anymore, only via PPA's. But indeed, with the whole IRQ threading thing
> being merged in the mainline kernel you could ask yourself, do I really
> need a real-time kernel. In my case I dare to say yes, haven't done any
> A-B testing with a low-latency kernel but I get the feeling that I can
> get the most out of a real-time kernel. That's why I'm thinking about
> switching to Arch but unfortunately the 3.0 real-time kernel is not
> stable enough (it crashes on any plug-in that uses the Juce framework,
> need to file a bugreport).

Get it filed then.  The quicker its filed, the quicker it will get fixed 
(if its not Juce's fault that is.)
 
> Best,
> 
> Jeremy

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: <http://coyoteden.dyndns-free.com:85/gene>
There's got to be more to life than compile-and-go.