Re: PROBLEM: USB keyboards works only 4 per PC host port

--- Alan Stern <stern@rowland.harvard.edu> wrote:

On Tue, 19 Aug 2008 juanslayton@dslextreme.com wrote:

quoted

If I understand your analysis, Aivils' problem is because the UHCI
controllers are too slow.

Not just that; it also is a question of scheduling.  The uhci-hcd
driver isn't very clever about scheduling, and it tries to put all the
packets into the same frame.  If the packets were distributed among
multiple frames then the limit would be considerably higher (eight
times higher in this case).

I'm not sure of the scheduling details in the ohci-hcd driver; they
might well be more flexible than in uhci-hcd.  In which case a single
OHCI controller would be able to handle up to 32 of these keyboards, 
even though it is no faster than a UHCI controller.

The OHCI scheduling is pretty simple and compact.  I'd think it would
be easy enough to make UHCI do the same sort of thing:  track bandwidth
assigned to 2^N frames (OHCI hardware imposes a smaller limit for N
than UHCI hardware does), and pick the least loaded of those frames to
use for new transfers.  In ohci-q.c see balance(), periodic_{,un}link().

Thing is that would involve changing how UHCI manages periodic transfers;
assuming it hasn't changed those structures since last I looked.


-------------------------------------------------------------------------
This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
Build the coolest Linux based applications with Moblin SDK & win great prizes
Grand prize is a trip for two to an Open Source event anywhere in the world
http://moblin-contest.org/redirect.php?banner_id=100&url=/