David Brownell wrote:
> > Because it's faster to just send the CLEAR_HALT than to actually stop and
> > look at the status -- other driver vendors have realized this, resulting in
> > some odd-looking but totally legal bus transactions which run very quickly.
>
> I can't buy this. The instructions requesting I/O cost more than the ones
> testing status, and then there's cost for the I/O cost itself.
But not when you have to have an interrupt before you can check status and thus miss
at least 1 usb
frame.
If the CLEARSTALL command is set up in the HCD together with the data urbs and is
executed after
they complete, that would be faster.
Also, going to the example of usb-storage, if the read status bulk urb is also set up
at this point
(and guaranteed not to start before the halt completed), this could save another
frame. (Depending
on how much time there is available in the frame?)
I am not familiar with the specifics of the *hci's, so I don't know if this is even
possible.
J.
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