[Xenomai-help] rtcan and USB legacy

[Xenomai-help] rtcan and USB legacy

[Roland Tollenaar]

Hi,

I have understood that USB legacy set to be on in the BIOS is a 
potential cause for latency issues. Is that correct?

I have it turned on due to the fact that I boot from USB. I'd like to 
know how severe the problems might be. Does anyone have experience with 
this?

Regards,

Roland.

Re: [Xenomai-help] rtcan and USB legacy

[Gilles Chanteperdrix]

Roland Tollenaar wrote:
 > Hi,
 > 
 > I have understood that USB legacy set to be on in the BIOS is a 
 > potential cause for latency issues. Is that correct?
 > 
 > I have it turned on due to the fact that I boot from USB. I'd like to 
 > know how severe the problems might be. Does anyone have experience with 
 > this?

I guess the answer depends on the BIOS implementation of the legacy
emulation. I suppose you can observe latencies around some tens of
microseconds.

That said:
- I really doubt that you need legacy USB emulation to boot from USB;
- in some cases, loading the Linux USB HCIs drivers is known to turn off
  the legacy USB emulation.

-- 


					    Gilles Chanteperdrix.

Re: [Xenomai-help] rtcan and USB legacy

[Roland Tollenaar]

>  > I have it turned on due to the fact that I boot from USB. I'd like to 
>  > know how severe the problems might be. Does anyone have experience with 
>  > this?
> 
> That said:
> - I really doubt that you need legacy USB emulation to boot from USB;
Why do you say this? I strongly had the impression that I needed to turn 
it on to get the system to boot from USB but turned it on together with 
another innocuous option. Maybe the innocuous option was not so innocuous?


> - in some cases, loading the Linux USB HCIs drivers is known to turn off
>   the legacy USB emulation.
This may be the case on this machine. I don't notice any detrimental effect.


Roland


>