From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Herbrechtsmeier Date: Fri, 20 Jul 2012 16:51:33 +0200 Subject: [U-Boot] [PATCH v2 2/5] ehci-hcd: Boost transfer speed In-Reply-To: <1211667297.335216.1342792578876.JavaMail.root@advansee.com> References: <1211667297.335216.1342792578876.JavaMail.root@advansee.com> Message-ID: <50097075.5010504@herbrechtsmeier.net> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Am 20.07.2012 15:56, schrieb Beno?t Th?baudeau: > 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. But if I am right, the max packet length is 512 for bulk and 1024 for Interrupt transfer. Regards, Stefan