Posted by Ilya Zakharevich on 01/21/08 15:46

[A complimentary Cc of this posting was sent to
John Navas
<spamfilter1@navasgroup.com>], who wrote in article <u7d9p3polkgjj6menqu4lhpkhjlvcinf8l@4ax.com>:
> >No. I do not see how the effect you describe can appear; device
> >drivers should not be affected by the "system being busy"; an
> >interrupt is an interrupt is an interrupt. I may be missing more
> >technical details...
>
> The USB bus isn't interrupt-driven -- it's polled (as I wrote),

Do not see any significant difference. The poller would set up a
wake-up call, which would generate an interrupt. [And, BTW, why my
PCI hardware view shows that USB controllers use interrupts?]

> which is why latency can be an issue.

Could you explain how latency is related to polling?

> When the host is busy servicing device 1,
> device 2 has to wait until the host is free (latency), which can be a
> problem when streaming at high speed, as in the case of video.

I do not see how this could be a problem - just do not use more than 1
USB device...

> The part you snipped on polling:

[part with no relation to polling (???!!!) skipped.]

Puzzled,
Ilya

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