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Date: Mon, 06 Jun 2011 16:25:19 +0200
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 13/31] usb-ehci: drop EXECUTING checks.
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To: David Ahern <daahern@cisco.com>
Cc: qemu-devel@nongnu.org

   Hi,

>>> -#if EHCI_DEBUG == 0
>>> -    if (qemu_get_clock_ns(vm_clock) / 1000>= ehci->frame_end_usec) {
>>> -        if (async) {
>>> -            DPRINTF("FETCHENTRY: FRAME timer elapsed, exit state machine\n");
>>> -            goto out;
>>> -        } else {
>>> -            DPRINTF("FETCHENTRY: WARNING "
>>> -                    "- frame timer elapsed during periodic\n");
>>> -        }
>>> -    }
>>> -#endif
>
> This check was added to per Section 4 of the EHCI spec -- the HC should
> not start transactions that will not be completed before the end of the
> micro-frame. If you remove this what causes the EHCI model to take a
> breather?

Look at patch #8.  That brings a number of state machine changes.  One 
of them is that the async schedule stops as soon as it notices it walks 
in circles (i.e. sees a QH the second time).

>>> -    case EST_FETCHENTRY:
>>> -        /* fall through */
>>
>> Why drop this case too? As I recall that is needed for proper execution.

The async schedule doesn't pause in fetchentry state any more (also done 
by patch #8).

cheers,
   Gerd