On Friday 24 April 2009, Kumar Gala wrote: > I'm hopping someone here might be able to help me understand better > what a USB Power fault condition is as referenced in the USB ULPI PHY > specifications. > > I'm trying to understand better under physical conditions a power > fault would be signaled to the PHY and possible to the USB host > controller. You want me to look at the ULPI spec for you? :) The two power faults that come to mind are both host side: - One relates to the A_WAIT_VRISE transition, whereby VBUS must become valid within 100 msec after certain events. In the best of all possible worlds, it's a nice gradual rise, no bumps. More typically, it's got a current spike and becomes briefly invalid ... which *ought* to be just fine, since 100 msec hasn't yet elapsed, but silicon has been known to flake out. - A similar one relates to current spikes *after* that transition. In those cases, overcurrent errors are perfectly reasonable to treat as errors. In short, VBUS going invalid in states other than the A_WAIT_VFALL transitions. Now, look at the spec and tell me where I goofed. ;) - Dave -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
