Bug in split transactions on Raspberry Pi

Alan Stern stern at rowland.harvard.edu
Mon Jan 25 13:51:42 PST 2016

On Mon, 25 Jan 2016, Peter Stuge wrote:

> Alan Stern wrote:
> > the device's embedded hub ACKs the packets from the PC and not the
> > packets from the RPi.
> > 
> > What other differences could there be?  Timing?  Power levels?
> Yes, both good candidates. Can you measure VUSB?

Distinctly higher than 5V.

> As for timing, the
> host controller will send SOF more or less regularly, if too
> irregular then that could cause problems for the device. Does your
> analyzer provide precise timestamps?

Yes, but the software doesn't want to display individual SOF packets.  
However I can see, for example, that 84 SOF packets were sent during a 
10.3-ms period.  Or 2048 were sent during a 256-ms period.  It seems 
pretty regular.

Alan Stern

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