[Xenomai] Dedicated Core?

Gilles Chanteperdrix gilles.chanteperdrix at xenomai.org
Mon Mar 31 13:29:45 CEST 2014


On 03/31/2014 12:04 AM, Charles Steinkuehler wrote:
> On 3/30/2014 4:41 PM, Gilles Chanteperdrix wrote:
>>
>> First, the imx6 is reported to have high latencies, and it is mostly due
>> to cache effects, so isolating the cpus will not help.
>>
>> Second, I would say relying on low user-space latencies to do in
>> user-space things that the kernel should do is a bad design. You would
>> have better success implementing the step motor control low level
>> details as a kernel driver, and only move the high level stuff in
>> user-space.
> 
> I am not looking to migrate something that should be a kernel service,
> instead I'm trying to replace having dedicated hardware.

Actually, this reminds me of a discussion we had some time ago, about 
generating PWM with omap3. You can find it here:
http://veter-project.blogspot.se/2011/09/real-time-enough-about-pwms-and-shaky.html
http://veter-project.blogspot.se/2012/04/precise-pwms-with-gpio-using-xenomai.html
http://comments.gmane.org/gmane.linux.real-time.xenomai.users/14026

In the end, Andrey succeeded to have precise control by using timers,
in kernel-space, instead of threads in user-space, and a little trick:
waking up early and spinning waiting for the target time.

-- 
                                                                Gilles.




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