iokit/IOKit/IOService.h

1373     Interested drivers must acknowledge power changes in <code>powerStateWillChangeTo</code> or <code>powerStateDidChangeTo</code>, either via return value or later calls to @link acknowledgePowerChange acknowledgePowerChange@/link.
1390 /*! @function acknowledgePowerChange
1392     @discussion When power management informs an interested object (via @link powerStateWillChangeTo powerStateWillChangeTo@/link or @link powerStateDidChangeTo powerStateDidChangeTo@/link), the object can return an immediate acknowledgement via a return code, or it may return an indication that it will acknowledge later by calling <code>acknowledgePowerChange</code>.
1393     Interested objects are those that have registered as interested drivers, as well as power plane children of the power changing driver. A driver that calls @link registerInterestedDriver registerInterestedDriver@/link must call <code>acknowledgePowerChange</code>, or use an immediate acknowledgement return from <code>powerStateWillChangeTo</code> or <code>powerStateDidChangeTo</code>.
1398     IOReturn acknowledgePowerChange( IOService * whichDriver );
1650     @result The driver returns <code>IOPMAckImplied</code> if it has prepared for the power change when it returns. If it has started preparing but not finished, it should return a number of microseconds which is an upper limit of the time it will need to finish preparing. Then, when it has completed its preparations, it should call @link acknowledgePowerChange acknowledgePowerChange@/link. */
1664     @result The driver returns <code>IOPMAckImplied</code> if it has prepared for the power change when it returns. If it has started preparing but not finished, it should return a number of microseconds which is an upper limit of the time it will need to finish preparing. Then, when it has completed its preparations, it should call @link acknowledgePowerChange acknowledgePowerChange@/link. */