There are five units in the timer device. TIMER DEVICE UNITS Unit Use ------------ --------------- UNIT_MICROHZ Interval Timing UNIT_VBLANK Interval Timing UNIT_ECLOCK Interval Timing UNIT_WAITUNTIL Time Event Occurrence UNIT_WAITECLOCK Time Event Occurrence * The VBLANK timer unit is very stable and has a granularity comparable to the vertical blanking time. When you make a timing request, such as "signal me in 21 seconds," the reply will come at the next vertical blank after 21 seconds have elapsed. This timer has very low overhead and may be more accurate then the MICROHZ and ECLOCK units for long time periods. Keep in mind that the vertical blanking time varies depending on the display mode. * The MICROHZ timer unit uses the built-in precision hardware timers to create the timing interval you request. It accepts the same type of command - "signal me in so many seconds and microseconds." The microhertz timer has the advantage of greater resolution than the vertical blank timer, but it may have less accuracy over long periods of time. The microhertz timer also has much more system overhead, which means accuracy is reduced as the system load increases. It is primarily useful for short-burst timing for which critical accuracy is not required. * The ECLOCK timer unit uses the Amiga E-Clock to measure the time interval you request. This is the most precise time measure available through the timer device. * The WAITUNTIL timer unit acts as an alarm clock for time requests. It will signal the task when systime is greater than or equal to a specified time value. It has the same granularity as the VBLANK timer unit. * The WAITECLOCK timer unit acts as an alarm clock for time requests. It will signal the task when the E-Clock value is greater than or equal to a specified time value. It has the same granularity as the ECLOCK timer unit. Granularity vs. Accuracy. ------------------------- Granularity is the sampling frequency used to check the timers. Accuracy is the precision of a measured time interval with respect to the same time interval in real-time. We speak only of granularity because the sampling frequency directly affects how accurate the timers appear to be.
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