Miles Sound System SDK 7.2a

AIL_set_timer_period

The function AIL_set_timer_period programs a timer for callback service at periods ranging from 1 microsecond to 1,000,000,000 microseconds (approximately 15 minutes).

void AIL_set_timer_period(
  HTIMER timer,
  U32 microseconds
);

In Parameters

timer: is a handle to the timer to program.
microseconds: specifies the desired callback interval in microseconds.

Discussion

Any one of three functions may be used to program a timer's callback rate. These functions are AIL_set_timer_period, AIL_set_timer_frequency, and AIL_set_timer_divisor. All three of these functions perform exactly the same task, but accept their values in different units. Period in microseconds, for example, is the reciprocal of frequency in megahertz. For fast timer repetition rates, greater precision may be obtained by expressing the timer period as its reciprocal, frequency, and using AIL_set_timer_frequency instead.

In practice, the fastest possible rate will be substantially slower than the theoretical value due to the host system's interrupt-processing overhead. MSS may exhibit internal stack overflows if any timer is programmed for a rate of more than a thousand or so calls per second. This does not necessarily indicate a fault in either the DOS extender or MSS, but is a sign that the PC hardware in use is incapable of keeping up with the demands of very-high-speed timer service in protected mode.

Under normal circumstances, the programmed timer service rate will exhibit a long-term accuracy of better than ± 100 parts per million (ppm). This accuracy figure may be somewhat degraded under certain environments such as Microsoft Windows.

The fastest possible timer period available under the Windows MSS API is 5 milliseconds (200 Hz) by default. This period limit may be changed to as little as 1 millisecond (1000 Hz) by changing the AIL_MM_PERIOD preference value immediately after calling AIL_startup.

Group: Timer Services
Related Functions: AIL_register_timer, AIL_set_timer_divisor, AIL_set_timer_frequency, AIL_set_timer_period, AIL_startup
Related Basic Types: HTIMER, MILES_PREFERENCES, U32, void