On Mon, Dec 19, 2011 at 10:08:55AM -0800, Sarah Sharp wrote: > On Mon, Dec 19, 2011 at 11:57:46AM -0500, Alan Stern wrote: > > Sarah: > > > > Do you have any experts on EHCI on tap at Intel? I've got some > > questions about the Interrupt on Async Advance Doorbell (IAAD) bit in > > the USBCMD register. The documentation is incomplete, inconsistent, > > and confusing. > > Sure, I'll forward your email to John Howard and Karthi, who were on the > list of authors of the EHCI spec. John says: This is a 'doorbell', the intent is a transition of 0b to 1b would 'ring' the doorbell (think edge-triggered event). The interrupt associated with this event occurs at the next interrupt threshold, at which time hardware will set the bit to 0b. The implications after the 0-1 transition and to the interrupt threshold are: The bit will persist as a 1b value. Software cannot cancel the event by writing a zero (0b) to the bit. Software can write the bit with any value it wants and it will have no effect. After the interrupt threshold time, the process resets. Does this help? Best Regards John H. -- 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
