atrtc4
At real-time clock (rtc) driver
Usage
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.enabled
-
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).
Overview
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.
Releases
34 releases since FreeBSD 9.0-RELEASE; the text changed 21 times.