On Thu, May 17, 2001, Dan Streetman <[EMAIL PROTECTED]> wrote:
> On Thu, 17 May 2001, Thomas Sailer wrote:
>
> >Dan Streetman schrieb:
> >
> >> The URB is not automatically resubmitted by the HCD.
> >
> >BTW, what is the difference between such a nonresubmitted
> >interrupt and a bulk transfer? Unless I'm missing something
> >they look exactly the same on the wire, so why add another
> >redundant interface?
>
> at least 3 differences (in order of importance, IMHO):
>
> 1.No low-speed bulk on UHCI
> It was pointed out by someone on this list that the uhci.c HCD does not allow
> low-speed Bulk URBs.
>
> 2.Polling interval
> The polling interval for bulk URBs is as-fast-as-possible. The device must
> NAK many times per frame, which may render the device useless (by taking up
> all it's microcontroller's processing time). Also this increases overall
> bus bandwidth usage.
>
> 3.Guaranteed polling
> Interrupt URBs are (supposed to be) guaranteed to poll at certain intervals.
> Bulk URBs are not, so it is possible that under high bus load the device
> is starved and data is lost. I know this is a very unlikely, remote case,
> but it is possible.
4. Bandwidth allocation
We don't do this perfectly yet, but we want to be able to do this
correctly
As far as I'm concerned, overloading bulk to do interrupt transfers has
too many problems.
JE
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