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

Stefan Herbrechtsmeier
2012-07-20T14:51:33Z

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