On Dec 29, 2011, at 8:14 PM, Brian Willoughby wrote:
> A) From the application viewpoint, is it expected that all possible process exit paths (AppKit, Unix signal, crash) involve a final Default Interface selection command?
>
If a user space application has changed the alternate interface of an IOUSBInterface when the application quits, unexpectedly or not, the USB stack will issue a SetAlternateInterface(0).
> B) From the USB Device firmware viewpoint, is it safe to assume that the Alternate Interface will be deselected before a new client application on the USB Host begins a new stream? In other words, is it safe to design the firmware to expect the Default Interface to be selected in between each Alternate Interface activation? If so, is it safe to assume that this will always happen even if the client application crashes or is rudely interrupted by Force Quit or a Unix signal?
See (A). However, this is just for user space applications. However, designing your device firmware to require a SetAlternateInterface(0) in between selections of other alternate interfaces seems fragile.
Good luck,
--
Fernando Urbina
USB Technology Team
Apple Inc.
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