Re: Question about xHCI

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On Sat, Apr 21, 2012 at 10:53:04PM +0800, Elric Fu wrote:
> 2012/4/21 Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx>:
> > On Thu, Apr 19, 2012 at 04:42:04PM -0400, Mike Vlad wrote:
> >>  The thing I don't understand is what xHCI really is, in simple terms. A driver? A hardware architecture?
> >
> > xHCI is a spec that defines the interface between the eXtensible Host
> > Controller (xHC) and software.  So it's an interface specification, that
> > defines both the registers that the hardware needs to expose, and the
> > data structures and behavioral model that a software driver needs to use
> > in order to communicate with the hardware.
> >
> > Basically, the 0.96 spec was released to allow third-party host vendors
> > to create PCIe add-in cards or stand-alone chips that OEMs could add to
> > their motherboard.  You can only integrate an xHC into a chipset (making
> > the hardware physically part of the chipset package) if you comply with
> > the xHCI 1.0 spec.
> 
> Hi Sarah,
> 
> I am a little confused. Thanks for your explanation. Actually, I never
> heard the differences between 0.96 and 1.0. I always thought 0.96
> was draft spec and 1.0 was official spec.

If you search the 0.96 spec, you won't find the word "draft".  There
were draft specs before 0.96, like the 0.95 draft spec.

The 0.96 spec was the first official xHCI specification that hardware
vendors could certify hardware against.  I think they can even still get
USB-IF certification for 0.96 hosts, but I could be wrong.

> So I have a question about
> it. Do you mean that the xHC adhere to xHCI 1.0 spec can't be PCIe
> add-in cards or stand-alone chips? I know some vendors produce
> stand-alone chip complies with xHCI 1.0 spec, such as NEC
> µPD720201. Did I make a mistake? or those chips don't strictly comply
> with xHCI 1.0?

Companies can still make an xHCI 1.0 host that is a discrete chip.
Nothing about the 1.0 spec stops them from doing that.  They just can't
make a 0.96 host that is integrated in a chipset.

Sarah Sharp
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