We have a bug on this already, and we are looking at what we can do
to fix it without breaking anything else.
It has to do with the fact that the port in question shares a Full
Speed controller with the internal keyboard/trackpad, which gets
suspended when it is not being used to save power.
You can mitigate this most easily by using a different port.
You can also insert a High Speed hub, which uses a different controller.
Other than that, just know that we are aware of the issue and are
working on a solution.
----------------------------
Rhoads Hollowell
USB Software Team
Apple Inc.
On Mar 9, 2007, at 10:15 AM, Mark Cookson wrote:
We’re streaming isoc audio on a MacBook or MacBook Pro and getting
occasional dropouts of audio that we’ve traced to being stalled for
about 10-20ms in a call to pipe->Write().
Also, it appears that the problem only happens on the rearmost USB
port on the MacBook, and it only happens after you press a key
after you haven’t pressed any keys for a while.The question is,
what can we do to avoid this? Are we somehow holding a lock that
IOUSBFamily needs? Could we change our order of operations to fix
this? Should we not be requesting an interrupt with every frame
(low latency isoc with updateFrequency = 1)? The fact that it only
happens on one MacBook port is very suspicious and makes me worried
that we can’t actually fix it on our end, but are there steps we
can take to mitigate its effects?
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