On Mon, 28 Jun 2004, Steve Calfee wrote:

> Hi Alan,
> 
> I don't think you are right about this. The spec for low and high speed 
> devices is very tight on bus turnaround times. A minimum of 2 bit times (166 
> ns) from the end of SE0 of the eop and a maximum of 6.5 bit times (541 ns). 
> See table 7-14 in the usb 2.0 spec. This is for FS and LS only - I guess by 
> definition since you are talking about UHCI and OHCI.

You're right (except that T_RSPIPD2 is 7.5 bit times), and the
corresponding numbers of nanoseconds would be different for low speed.  I
got the numbers wrong through trying to reproduce them from memory and
probably calculating the bits->nanoseconds conversion wrong in the first
place.

So maybe Tommy's UHCI controller rejects an interpacket delay of 540 ns 
and the OHCI controller accepts it.  This is just an hypothesis, since we 
don't have any way to see what's really going on.

Tommy: An interesting test, if you can do it, would be to install Windows
on the same computer and see if the wifi stick works with it.

Alan Stern






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