Re: [Xenomai] BeagleBone Xenomai Latency

[Charles Steinkuehler <charles@steinkuehler.net>]

On 1/12/2014 2:29 PM, Gilles Chanteperdrix wrote:
> On 01/11/2014 09:58 PM, Charles Steinkuehler wrote:
>> Recommended but not selected (causes linking errors apparently due to
>> the kernel size being too large for some of the limited reach thumb2
>> jump/branch instructions):
> 
> You mean thumb2? Did you enable the workaround for buggy gas?

Yes, thumb2, and yes, the buggy gas workaround was enabled (by default
when selecting a thumb2 build).  Googling the resulting errors brought
up some threads about iMX6 kernel builds failing the same way, which is
where I got "too big for some jump/branch instructions" which I also
translate as "beyond my currently capability to fix with any expectation
that I'm not introducing other issues".  :)

>> OVERALL RESULTS:
>> Adding the recommended options dramatically helped with latency when
>> iPipe trace was enabled, but not so much for the normal kernel.  I did
>> see typical and best case latency drop significantly (by about 25%) with
>> the recommended options, but worst-case latency for both kernels
>> remained around 50 uS.
> 
> I also get 50us at 1kHz, I only get 40us at 10kHz.

Good, it sounds like we're seeing basically the same numbers.  I can
live with the 50 uS latency, which is already significantly better than
I was expecting since I hadn't done testing for a while.

-- 
Charles Steinkuehler
charles@steinkuehler.net

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