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atrtc — AT Real-Time Clock (RTC) driver
This driver is a mandatory part of i386/amd64 kernels. The following tunables are settable from the loader(8): hint.atrtc.X.clock controls event timers functionality support. Setting to 0, disables it. Default value is 1. hw.atrtc.enable Forces enabling or disabling of the device(s). Setting to 0 disables it, setting to 1 enables it, bypassing any platform configuration hints. Default value is -1 (autodetect).
This driver uses RTC hardware to supply kernel with time-of-day clock with 1 second resolution and one event timer. This hardware uses base frequency of 32768Hz for advancing time-of-day clock and generating periodic interrupts. Interrupts could be generated with fixed number of frequencies, from 2Hz to 8192Hz, obtained by dividing base frequency by one of supported power-of-2 divisors. Event timer provided by the driver is irrelevant to CPU power states.
apic(4), attimer(4), eventtimers(4), hpet(4)