[U-Boot] [PATCH v2 2/5] ehci-hcd: Boost transfer speed

Marek Vasut marex at denx.de
Fri Jul 20 15:44:01 CEST 2012


Dear Benoît Thébaudeau,

> On Friday 20 July 2012 13:37:37 Stefan Herbrechtsmeier wrote:
> > Am 20.07.2012 13:26, schrieb Benoît Thébaudeau:
> > > +			int xfr_bytes = min(left_length,
> > > +					    (QT_BUFFER_CNT * 4096 -
> > > +					     ((uint32_t)buf_ptr & 4095)) &
> > > +					    ~4095);
> > 
> > Why you align the length to 4096?
> 
> It's to guarantee that each transfer length is a multiple of the max packet
> length. Otherwise, early short packets are issued, which breaks the
> transfer and results in time-out error messages.

Early short packets ? What do you mean?

> Regards,
> Benoît

Best regards,
Marek Vasut


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