Re: [Xen-devel] Xen for real-time/embedded/automotive

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On gio, 2013-11-28 at 11:39 +0000, Simon Martin wrote:
>  
> > BTW, I do realise only know that I probably never asked that... What
> > is 
> > (if you feel like saying it here) your specific usecase / final goal
> > of 
> > this work? 
> >  
> I am porting an motion control system to Xen. The OS and hardware is
> developed in house. I originally wrote the OS about 20 years ago on a
> TI DSP processor with 32 k words of RAM and it has been evolving since
> then, migrating to different processors (MIPS/ARM) and an ever
> increasing amount of memory (we moved from SRAM to DRAM when we went
> on to the MIPS platform, and the smallest DRAM chips you could get at
> the time were 1 MB).
>
That's very cool! You know, at some point, probably when you/we would
have a bit more of this in place, I'll probably ask if you want to write
a post on our blog (http://blog.xen.org/) about it! :-D
 
> Looking at the Real-Time Xen project, it is built around millisecond
> resolution. That was fine for motion control about 20 years ago, but
> nowadays everyone is working sub-millisecond. 
>
Yeah, well, let's investigate what the limit is and try to push harder
on it then. From my previous experience with real-time on Linux, it's
possiblee to go sub-milliseconds, although not without some tricks.
Personally, I think it's both possible and worthwhile to try to figure
out what are the tricks required for us to get as near as possible to
that!

> Our existing systems can close the control loop every 125 Âs doing
> full interpolation on 8 axes with 64 bit resolution on an ARM11
> platform. Worst than that, jitter on the control loop gives you at
> best jerky movement and at worst shuts down the drives so that must be
> controlled.
>  
HeHe... It's about Linux, but I just can't resist:

<<Controlling a laser with Linux is crazy, but everyone in this room is
crazy in his own way. So if you want to use Linux to control an
industrial welding laser, I have no problem with your using
PREEMPT_RT.>> Torvalds, Linus (2007)

Of course, substitute 'Linux' with 'Xen', and PREEMPT_RT with either
RT-Xen, or whatever we could come up with in the long run! :-P :-P

Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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