On Wednesday 15 June 2011 11:33:14 Alexander Best wrote:
> On Tue Jun 14 11, Hans Petter Selasky wrote:
> > On Tuesday 14 June 2011 14:52:08 Alexander Motin wrote:
> > > Hans Petter Selasky wrote:
> > Done:
> > 
> > http://svn.freebsd.org/changeset/base/223098
> 
> btw., if i might ask a technical and probably naive question:

Hi,

> 
> does USB 3.0 feature *full* backward compatibility? that is supporting usb
> 1.x and usb 2.0 devices without the need for enabling those legacy
> controllers?

Yes, XHCI is a replacement for EHCI and OHCI and UHCI. It speaks multiple 
protocols.

> 
> so will xhci give me all the backward compatibility or do i have to also
> enable a combination of ohci/uhci/ehci? with usb 2.0 there was no usb 1.x
> support unless ohci/uhci was also enabled.
> 
> i read that the xhci controllers don't depend on CPU and I/O availability
> as much as the old controllers. doing CPU intensive tasks shouldn't have
> such a massive effect on USB transfer times, compared to usb 1.x and 2.0.
> that's why i'd like to completely get rid of the need for ohci/uhci/ehci
> in my kernel config.

Due to certain commercial OS'es which haven't got XHCI support, hardware 
manufacturers have come up with creative solutions which involves custom bits 
to switch ports to and from XHCI/EHCI.

> i'd really like to see some transfer time statistics with CPU being close
> to 100% idle and with CPU being hammered close to 100% with usb 3.0. i
> think i did such a test a while ago for usb 2.0 and transfer rates dropped
> quite significantly.

--HPS
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