2005/9/5, Alan Stern <[EMAIL PROTECTED]>:
> On Mon, 5 Sep 2005, Franck wrote:
>
> > > And NAK response to an interrupt transfer definitely _should_ be retried,
> > > at the next interrupt period.
> >
> > ok so I definetly can't use this feature for interrupt polling and
> > isoc transfer.
>
> I don't understand. How does the feature work, and why can't you use it?
>
well, the feature allows the hardware to automatically restart a
transaction when the function previously handshaked it with a NAK. If
the function is a hub and the transaction is used to poll its endpoint
1...the hub will send NAK as long as there's no change on its ports.
Therefore the hardware will be busy to restart the transaction until
there's a change on the hub's ports...That's why I said that I could
not use this feature for interrupt polling.
> > but if the NAKed transaction lasts more than a frame ?
>
> What do you mean? A transaction can never last more than a frame. The
> longest possible full-speed transaction is a 1023-byte ISO transfer, and
> that takes less than 1 ms. The longest possible bulk/interrupt/control
> transaction is 64 bytes, which is considerably shorter.
>
> Perhaps you mean "What if the device keeps NAKing for longer than a
> millisecond?" That's okay; devices are allowed to NAK for several
> seconds, sometimes even longer. You should just keep retrying until the
> transfer completes or is unlinked.
>
Yes, I tried to mean that :)
When you say that I should just keep retrying until transfer completes
or unlinked. Does that mean I should start the next frame with the
NAKed transaction even if there are isoc transactions scheduled for
that frame ?
Thanks.
--
Franck
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