[speedtouch] Re: isochronous support broken?

Alistair John Strachan s0348365 at sms.ed.ac.uk
Mon Jan 23 09:59:51 EST 2006

On Monday 23 January 2006 12:36, Duncan Sands wrote:
> Hi Alistair,
> > usb 4-1.4: reset full speed USB device using ehci_hcd and address 4
> a bug fix for ehci + iso urbs bandwidth allocation just got posted to the
> usb mailing list.  So I suggest trying uhci instead (OK, I just saw that
> you tried it).
> ...
> > As you can see, the recv buffer has dropped but nothing has changed. Then
> > I had the idea to remove ehci-hcd, and force it to use uhci-hcd for the
> > USB 1.1 device (I have no USB 2.x devices anyway). This was successful:
> ...
> > I was able to bring pppd up over the interface. /proc/bus/usb/devices
> > looks like this; only 79% utilisation.
> What do you mean by "79% utilisation"?
> > T:  Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=12  MxCh= 2
> > B:  Alloc=710/900 us (79%), #Int=  2, #Iso=  4

This, which I assume is bus utilisation.

> > D:  Ver= 1.10 Cls=09(hub  ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
> > P:  Vendor=0000 ProdID=0000 Rev= 2.06
> > S:  Manufacturer=Linux uhci_hcd
> > S:  Product=UHCI Host Controller
> > S:  SerialNumber=0000:00:10.0
> > C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=  0mA
> > I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
> > E:  Ad=81(I) Atr=03(Int.) MxPS=   2 Ivl=255m
> >
> > My bandwidth is still locked to just under 500KB/s (4MBits). So either a)
> > isoc isn't working or b) you need to do more than just switch from bulk
> > to isoc to get 8Mbits from this device.
> This is what I see.  Using bulk I max out at a bit under 4 megabaud.  With
> isoc I max out at an even slower rate!
> > The Windows workaround does not suggest this, but I suppose it is
> > impossible to tell.
> What is "the windows workaround"?  (I don't have windows, which makes
> comparing with windows a bit awkward for me).

To go from Bulk to Isochronous. See here:


And here:


> > If it's a useful datapoint, I used to get sporadic errors and the USB LED
> > would flash RED if the bandwidth was held close to 4Mbit for a long
> > period of time. This no longer seems to happen with isoc, suggesting the
> > bandwidth bottleneck has been lifted. However, I do not see the 6.6
> > megabits I've synced at.
> Are you talking about linux or windows here?  Can you get 6.6 mb with
> windows?

I've not seen it myself, but supposedly it is possible (given the comments on 
many forums, such as adslguide.org.uk).

> Anyway, I think it likely that there is something wrong with the driver. 
> But it could be a hardware limitation.  Testing with windows should clear
> that up.  If you can do some experiments with windows, that would be great.

I'd like to help in any way I can, but putting Windows on the machine routing 
our internet is out of the question. It also probably wouldn't work, given 
the speed of that machine.


'No sense being pessimistic, it probably wouldn't work anyway.'
Third year Computer Science undergraduate.
1F2 55 South Clerk Street, Edinburgh, UK.

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