NdisSetCoalescableTimerObject function

The NdisSetCoalescableTimerObject function sets a timer object that the operating system coordinates with other timers, typically to reduce power consumption, when the exact expiration of the timer is not important to driver operation.


BOOLEAN NdisSetCoalescableTimerObject(
  NDIS_HANDLE   TimerObject,
  LONG          MillisecondsPeriod,
  PVOID         FunctionContext,
  ULONG         Tolerance



A handle to a timer object that NDIS provides when a driver calls the NdisAllocateTimerObject function.


The absolute or relative time at which the timer will expire. If the value of the DueTime parameter is negative, the expiration time is relative to the current system time. Otherwise, the expiration time is absolute. The expiration time is expressed in system time units (100-nanosecond intervals). Absolute expiration times track any changes in the system time; relative expiration times are not affected by system time changes.


The optional periodic time interval, in milliseconds, that elapses between every instance when the timer fires and the next call to the NetTimerCallback function, unless the timer is canceled. The value of this parameter must be less than or equal to MAXLONG. This parameter can be set to zero to indicate that the timer is non-periodic.


A pointer to a caller-supplied context area that NDIS passes to the associated NetTimerCallback function when a timer fires. If this parameter is NULL, NDIS uses the default value that is specified in the NDIS_TIMER_CHARACTERISTICS structure.


The tolerance, in milliseconds, between the timer period specified by MillisecondsPeriod and the initial time interval specified by DueTime . A periodic timer will first expire in the time interval between ( DueTime - Tolerance ) and ( DueTime + Tolerance ). The time interval between two later expirations of a periodic timer will be in the range of ( MillisecondsPeriod - Tolerance ) and ( MillisecondsPeriod + Tolerance ).

Return Value

NdisSetCoalescableTimerObject returns TRUE if the timer object was already in the system timer queue; otherwise, it returns FALSE.


A timer object set by this function operates the same as a timer set by NdisSetTimerObject, with an additional tolerance value added to the expiration parameter DueTime . The operating system uses this additional tolerance value to adjust the expiration time of the timer to coincide with the expiration of other software timers. By doing this, the operating system can reduce power consumption and improve energy efficiency.

NdisSetTimerObject operates similarly to NdisSetCoalescableTimerObject when Tolerance is set to zero.

After a driver calls NdisSetCoalescableTimerObject, the timer object is queued until expiration of an interval that is in the range of ( DueTime - Tolerance ) and ( DueTime + Tolerance ). After the interval expires, the operating system removes the timer object from the queue, and the caller-supplied NetTimerCallback function is run one time at IRQL = DISPATCH_LEVEL as soon as a processor becomes available.

If a nonzero value is specified in the MillisecondsPeriod parameter, the timer object is queued again until an interval in the range of ( MillisecondsPeriod - Tolerance ) and ( MillisecondsPeriod + Tolerance ) expires. After this interval expires, the timer object is resubmitted to the queue, and the caller-supplied NetTimerCallback function is run one time at IRQL = DISPATCH_LEVEL as soon as a processor becomes available.

To use timer coalescing effectively, a caller should specify a Tolerance value of at least 32 milliseconds. This value equals approximately two default system clock intervals of 15.6 milliseconds. Use a larger Tolerance value if you can do this, such as 100 milliseconds.

We recommend that MillisecondsPeriod and Tolerance be set to multiples of 50 milliseconds. Typical MillisecondsPeriod values are 50, 100, 250, 500, and 1000 milliseconds. Typical Tolerance values are 50, 100, 150, and 250 milliseconds.

Typically, a timer with a large MillisecondsPeriod value can use a proportionally large Tolerance value. For example, a timer with MillisecondsPeriod = 500 milliseconds might use Tolerance = 50 milliseconds. But a timer with MillisecondsPeriod = 10 seconds might use Tolerance = 1 second.

For more information about timer behavior, see KeSetTimerEx.

To cancel a timer, call the NdisCancelTimerObject function.


Minimum supported client Supported in NDIS 6.20 and later.
Target Platform Universal
Header ndis.h (include Ndis.h)
Library Ndis.lib

See Also