Re: [Libusb-devel] interrupt Xfer timeout problem

[Tim R. <ti...@pr...>]

Manfred Weiss wrote:
>
> Am 29.09.2009 um 19:28 schrieb Tim Roberts:
>>
>> Do you know what brand of USB host controller is on your motherboard?
>
> USB Controller: Intel Corporation 82801I (ICH9 Family) USB UHCI
> Controller
> USB Controller: Intel Corporation 82801I (ICH9 Family) USB2 EHCI
> Controller
>
> i am on the ehci...

Well, that's a recent and pretty reliable controller.


>> What is the packet size and interval in your interrupt pipe's
>> descriptors?

You didn't answer this question.  Let me give you an example of why this
is important.

You are asking for 512 bytes.  Let's say your interrupt pipe has a
maximum packet size of 16 bytes.  In that case, it will take 32
transfers before your buffer is filled.  If you had specified an
interval of 5 (meaning one transfer every 2 ms), it will take 64ms for
32 transfers to happen.

So, with those parameters, you will NEVER transfer 512 bytes in 35ms. 
You'd always get the timeout.

Is your hardware actually transferring full packets every time you ask
for data?

-- 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.