On Thursday 13 December 2007, Jay Monkman wrote:
> If I plug the audio device into a hub which is plugged into the system, it
> works fine. If I plug the audio device into the system directly
> (without a hub), it doesn't work. It seems to read and write some
> data, but very slowly - it iterates through the read/write loop about
> 1/50 as fast as when I use a hub.
>
> ...
>
> Thanks for your help. No, it only has the EHCI controller. I was
> mistaken about the root hub - it has 2 ports, although only one is
> connected to a transceiver. The manual for this CPU is at
>
> http://www.freescale.com/files/32bit/doc/ref_manual/MPC8349ERM.pdf
Looks like the same problem some other folk have reported with
those ARC-derived EHCI cores.
My diagnosis is that the TT scheduling code doesn't understand
about the TT integrated into the root hub ("without a(n external)
hub") ... whereas it behaves much better when using the TT(s)
found in external hubs.
There are other issues with ISO scheduling, notably that it's not
as smart is it might be, but those would show up equally well with
the external hub. So the issues you're seeing are not those.
- Dave
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