/****************************************************************************** * * FUNCTION: AcpiGetTimerDuration * * PARAMETERS: StartTicks - Starting timestamp * EndTicks - End timestamp * TimeElapsed - Where the elapsed time is returned * * RETURN: Status and TimeElapsed * * DESCRIPTION: Computes the time elapsed (in microseconds) between two * PM Timer time stamps, taking into account the possibility of * rollovers, the timer resolution, and timer frequency. * * The PM Timer's clock ticks at roughly 3.6 times per * _microsecond_, and its clock continues through Cx state * transitions (unlike many CPU timestamp counters) -- making it * a versatile and accurate timer. * * Note that this function accommodates only a single timer * rollover. Thus for 24-bit timers, this function should only * be used for calculating durations less than ~4.6 seconds * (~20 minutes for 32-bit timers) -- calculations below: * * 2**24 Ticks / 3,600,000 Ticks/Sec = 4.66 sec * 2**32 Ticks / 3,600,000 Ticks/Sec = 1193 sec or 19.88 minutes * ******************************************************************************/