Message 4 of 5
22 May 18 02:14
Join Date: 28 Jan 2005
Posts To This List: 11955
Driver Details of USB3 Debugging
On May 21, 2018, at 10:22 PM, firstname.lastname@example.org wrote:
> Thanks for the clarification. I missed the part talking about the
> special cable. Luckily I didn't waste any time trying to debug with a
> normal A to A cable.
Well, an A to A cable is not really "normal". I don't know what you'd use that
> I am still suprised this trick is being used. Are you able to clarify
> how each controller acts like a host?
The two hosts are not electrically connected. The "special sauce" cable has two
USB interface chips and a microcontroller that passes data back and forth.
Software on the two PCs probably negotiates their own protocol that ends up with
one side being a master, but in USB terms, both ends are devices.
> I suppose I can understand having no software mediated crossover, but there
are other parts of
> the protocol that I do not think would work over a special cable.
Oh, there is software involved. There's a processor inside that cable that
interface between the two buses, buffering and forwarding packets.
There was a USB debug capability added to EHCI, but it was more or less an
afterthought. It never really worked very well, and it was not universally
> Having read some of the spec it looks like they only implemented a
> very limited new protocol. I find this odd. I would have expected USB
> IP to be reused more than it is, and for USB OTG IP blocks to have
> been modified for use in computers proper.
Interesting point. It's not trivial to figure out how to incorporate OTG into
full Windows. It doesn't fit well with the driver model. Perhaps it was easier
to port the hacked in EHCI debug capability into XHCI.
Tim Roberts, email@example.com
Providenza & Boekelheide, Inc.