From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?utf-8?Q?Beno=C3=AEt_Th=C3=A9baudeau?= <benoit.thebaudeau@advansee.com>
Date: Fri, 20 Jul 2012 15:56:18 +0200 (CEST)
Subject: [U-Boot] [PATCH v2 2/5] ehci-hcd: Boost transfer speed
In-Reply-To: <201207201544.01904.marex@denx.de>
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To: u-boot@lists.denx.de

Dear Marek Vasut,

On Friday 20 July 2012 15:44:01 Marek Vasut wrote:
> > On Friday 20 July 2012 13:37:37 Stefan Herbrechtsmeier wrote:
> > > Am 20.07.2012 13:26, schrieb Beno?t Th?baudeau:
> > > > +			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?

During a USB transfer, all packets must have a length of max packet length for
the pipe/endpoint, except the final one that can be a short packet. Without the
alignment I make for xfr_bytes, short packets can occur within a transfer,
because the hardware starts a new packet for each new queued qTD it handles.

Best regards,
Beno?t