Re: single bit errors on files stored on USB-HDDs via USB2/usb_storage

[Ben Nizette <ben.nizette@iinet.net.au>]

Oliver Neukum wrote:
> Am Samstag, 9. Dezember 2006 07:11 schrieb Ben Nizette:
> > > > > Also, you mentioned that the corruption occurs systematically on certain
> > > > > byte patterns. Therefore it's certainly not related to the cables.
> > > > It'd guess that too, but who can that say for sure. :-|
> > > You may have a bit pattern that stresses the controllers and suddenly
> > > a marginal cable may matter.
> > The errors occur in strings of 0xFFs.  From the USB standard:
> >
> > a “1” is represented by no change in level and a “0” is represented by a 
> > change in level
>
> Yes, plus added stuffing bits.
>
> > so this error-infested bytes are effectively long, quiet times on the 
> > wire.  I would have thought this would be the _least_ stressful time for 
> > the controllers but maybe they are also more susceptible to noise during 
> > this period.
>
> The longer you don't change the voltage the likelier are reciever and
> transmitter to get out of sync.

Yes, hence the bit-stuffing, you're right :).  And hence this period 
isn't really too stressful for the controller as the stuffed bits come 
relatively often.

We're hoping that any wire-errors get picked up by the CRC anyway so a 
marginal cable under any circumstances shouldn't silently corrupt data. 
 I love that word 'shouldn't' ;)

Regards,
	Ben.
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