Hi,
I hadn't seen the 5-limit anywhere lately either,
and I looked for it a few weeks ago unsuccessfully.
However, I don't usually spend much time looking at
"Chapter 7: Electrical", but that's where it is since
it is (worst case) timing-related.
On pdf page 150 or spec page 134, at the top:
"Figure 7-31 depicts the configuration of six signal hops
(cables) that results in allowable worst-case signal
delay. The maximum propagation delay from the upstream end
of a hub's cable to any downstream port connector is 70ns."
Note that this doesn't STRICTLY say a limit of 5 hubs ("six
signal hops"), but that's what the graphic there shows.
It's also what all of the USB Compliance/Interoperability
Gold-Tree test configurations show IIRC.
The USB 2.0 spec will be public soon. It clarifies
this a bit better.
~Randy
> -----Original Message-----
> From: Kai Lahmann [mailto:[EMAIL PROTECTED]]
> Sent: Monday, April 24, 2000 12:32 PM
> To: [Linux-Usb]; Lennart Augustsson
> Subject: RE: [linux-usb] more than 7 ports on a hub?
>
> > -----Original Message-----
> > From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On Behalf
> > Of Lennart Augustsson
> > Sent: Monday, April 24, 2000 12:48 PM
> > To: Brad Hards
> > Cc: [EMAIL PROTECTED]
> > Subject: Re: [linux-usb] more than 7 ports on a hub?
> >
> > Brad Hards wrote:
> >
> > > As a secondary issue, would / should this count as two hubs in the
> > > maximum topology depth? And can anyone provide a
> reference for why five
> > > is the maximum depth - a quick scan of the USB spec only
> came up with
> > > section 6.4.4 which talks about excessive depth, but
> doesn't say what is
> > > excessive.
> >
> > Well, the number 5 is in there somewhere.
>
> I'm not sure, but I think I read in my Hub-Documentation
> somethink about 7?!?
>
> >
> > > I thought that it was driven by timing and the 5 metre
> > > cables, but that wouldn't seem to apply in this case.
> >
> > It's mostly driven by the hub timing. With maximum length cables
> > and maximum
> > hub depth there are only a few nanoseconds to spare in the
> worst case.
> > A design where two hubs are on the same PCB would safe the cable
> > propagation
> > delay, but this would not be enough for another hub (I've not
> > checked the figures,
> > I must admit).
> > I just had a similar problem with the D-link serial adapter. It
> > has a hub in it, with
> > just one of the ports used for the actual serial adapter. The
> > design is a mystery to me
> > since the other ports are unused.
> >
> > --
> > -- Lennart
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