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 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?
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, Benoît _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
