RTAI LiveCD + USB + High latencies

[Panagiotis Issaris]

Hi Philippe,

Philippe Gerum wrote:

>In short, this box has UHCI-compliant USB hardware, but
>config-2.6.9-adeos used in recent LiveCDs does not enable the UHCI host
>support (CONFIG_USB_UHCI_HCD).
>  
>
[...]

>I suspect that on this box with no user-accessible USB control at BIOS
>level, the legacy USB mode is enabled at boot time by the BIOS, which
>mode is known to induce large jittery (250 - 300 us on average for all
>latency tests, LXRT and fusion included).
>  
>
I've added the various USB host controller drivers to the new LiveCD
and noticed that my laptop's (Dell Inspiron 2650) maximum latency
seems to drop from about 2ms to 500us (*). Furthmore, the maximum latency
eve stays below about 15us for some seconds, then unfortunately goes up to
about 500us.

By repeatedly rerunning the test and restarting it as soon as the max 
latency
rose, I noticed that the period of the event (some SMI interrupt probably?)
happening is 1 minute.

The previously mentioned entries using the same Dell laptop:
http://issaris.org/rtai/show_entry.php?ts=2004-12-18+09%3A36%3A58%2B01
http://issaris.org/rtai/show_entry.php?ts=2004-11-25+16%3A41%3A13%2B01


With friendly regards,
Takis

* I must confess that I haven't run the test for a long time (30 seconds 
or so) yet, but the previous
runs of the LiveCD gave 2ms max latency nearly immediately.

-- 
------------------------------------------------------------------------
Panagiotis Issaris
Katholieke Universiteit Leuven
Division Production Engineering,
Machine Design and Automation
Celestijnenlaan 300B              panagiotis.issaris at mech.kuleuven.ac.be
B-3001 Leuven Belgium                 http://www.mech.kuleuven.ac.be/pma
------------------------------------------------------------------------