Re: [Patch] Increase USBFS Bulk Transfer size

Johannes Stezenbach
2011-10-16T09:10:23Z

On Sat, Oct 15, 2011 at 03:04:28PM -0400, Alan Stern wrote:
> On Sat, 15 Oct 2011, Johannes Stezenbach wrote:
>
> > What I meant to say is Markus' statement that the device only
> > works at a certain transfer size cannot be true since
> > this size is not visible to the device via the USB bus.
>
> That's what I would expect, too. But did you take a look at the usbmon
> traces Markus acquired?
>
> http://marc.info/?l=linux-usb&m=131845614819045&w=2

I glanced at them for 3 seconds, but I cannot be bothered
to analyze them in detail. The ASCII usbmon traces don't
show full USB packet contents anyway so you can't see if
partial MPEG TS packets are missing.

> They aren't completely definitive because the communications between
> the computer and the device _before_ the bulk transfers started were
> different. However they do clearly show the device working with
> 24064-byte transfers and not working with 12288+11776-byte transfers.

The device transfers data in the "not working" case, it's just that
the MPEG TS sync byte is not where Markus expects it, which could
be explained by a partial MPEG TS packet left in the device's FIFO
from previous interaction.

Johannes