Re: [Libusb-devel] Ubuntu10.10 urb submit error with libusb0.1.12

[Xiaofan C. <xia...@gm...>]

On Wed, Feb 23, 2011 at 1:42 AM, Tim Roberts <ti...@pr...> wrote:
> I'm surprised by the number of people doing new projects with
> isochronous pipes.  In my view, unless you are doing audio or video,
> there are virtually no good scenarios for isochronous pipes.  And if you
> are doing audio or video, you should be doing Audio Class or Video
> Class, in which case you don't need to be writing a driver anyway.
>

How do you like the explanation in the Cypress page?
http://www.cypress.com/?id=4&rID=33333

The answer is specific to Windows. But Linux and Mac OS X
and BSDs are not real-time OS so the answer might apply as well.

"Question: Is it advisable to use isochronous transfers for developing a
USB device? What are the problems related to isochronous transfers
from the Host (PC) side. Is the PC not fast enough to handle these
transfer or is it the drivers limitations?

Answer: The isochronous-transfer specification assumes that the Host
side is running a real-time operating system. Unfortunately, Windows
ISN'T a real-time OS, so iso transfers under Windows do not always
behave according to the specification. It is advisable, to avoid using
isochronous transfers for anything that's not supported by a
Microsoft-supplied Class Driver".

On the other hand, I think if the OS support is better, isochronous
transfer can be used for many device as well due to the guaranteed
bandwidth. So maybe in the end it is the lack of good drivers
which is the problem, not isochronous transfer itself.



-- 
Xiaofan