/share/man/man4/atrtc.4

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25.\" $FreeBSD$
26.\"
27.Dd September 17, 2010
28.Dt ATRTC 4
29.Os
30.Sh NAME
31.Nm atrtc
32.Nd AT Real-Time Clock (RTC) driver
33.Sh SYNOPSIS
34This driver is a mandatory part of i386/amd64 kernels.
35.Pp
36The following tunable is settable from the
37.Xr loader 8 :
38.Bl -ohang
39.It Va hint.atrtc. Ns Ar X Ns Va .clock
40controls event timers functionality support. Setting to 0, disables it.
41Default value is 1.
42.El
43.Sh DESCRIPTION
44This driver uses RTC hardware to supply kernel with time-of-day clock
45with 1 second resolution and one event timer.
46This hardware uses base frequency of 32768Hz for advancing time-of-day clock
47and generating periodic interrupts.
48Interrupts could be generated with fixed number of frequencies, from 2Hz to
498192Hz, obtained by dividing base frequency by one of supported power-of-2
50divisors.
51.Pp
52Event timer provided by the driver is irrelevant to CPU power states.
53.Sh SEE ALSO
54.Xr apic 4 ,
55.Xr attimer 4 ,
56.Xr eventtimers 4 ,
57.Xr hpet 4