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.
--
Dan Streetman
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