apic(4) [freebsd man page]

APIC(4) 						   BSD Kernel Interfaces Manual 						   APIC(4)

NAME

     apic -- Advanced Programmable Interrupt Controller (APIC) driver

SYNOPSIS

     This driver is a mandatory part of amd64 kernel.  To compile this driver into i386 or pc98 kernel, place the following line in your kernel
     configuration file:

	   device apic

     The following tunable is settable from the loader(8):

     hint.apic.X.clock
     controls event timers functionality support. Setting to 0, disables it.  Default value is 1.

     hint.apic.X.disabled
     Set this to 1 to disable APIC support, falling back to the legacy PIC.

DESCRIPTION

     There are two components in the Intel APIC system, the local APIC (LAPIC) and the I/O APIC.  There is one local APIC in each CPU in the sys-
     tem.  There is typically one I/O APIC for each peripheral bus in the system.

     Local APICs manage all external interrupts for a specific processor.  In addition, they are able to accept and generate inter-processor
     interrupts (IPIs).

     I/O APICs contain a redirection table, which is used to route the interrupts they receive from peripheral buses to one or more local APICs.

     Each local APIC includes one 32-bit programmable timer.  This driver uses them to supply kernel with one event timer named "LAPIC".  Event
     timer provided by the driver supports both one-shot an periodic modes.  Because of local APIC nature it is per-CPU.  The timer frequency is
     not reported by the platform and so automatically measured by the driver on the first use.  Depending on CPU model this timer may stop in C3
     and deeper CPU sleep states.  Driver automatically adjusts event timer priority and reports it to prevent entering dangerous sleep states
     when it is used.

SEE ALSO

     atrtc(4), attimer(4), eventtimers(4), hpet(4)

BSD
								 December 20, 2011							       BSD

ATTIMER(4)						   BSD Kernel Interfaces Manual 						ATTIMER(4)

NAME

     attimer -- i8254 Programmable Interval Timer (AT Timer) driver

SYNOPSIS

     This driver is a mandatory part of x86 kernels.

     The following tunables are settable from the loader(8):

     hint.attimer.X.clock
     controls support for the event timer functionality.  Setting this value to 0 disables it.	The default value is 1.

     hint.attimer.X.timecounter
     controls support for the time counter functionality.  Setting this value to 0 disables it.  The default value is 1.

     hw.i8254.freq
     allows overriding the default counter frequency.  The same value is also available at run-time via the machdep.i8254_freq sysctl.

DESCRIPTION

     This driver uses i8254 Programmable Interval Timer (AT Timer) hardware to supply the kernel with one timecounter and one event timer, and to
     generate sound tones for the system speaker.  This hardware includes three channels.  Each channel includes a 16 bit counter which decreases
     with a known, platform-dependent frequency.  Counters can operate in several different modes, including periodic and one-shot.  The output of
     each channel has platform-defined wiring: one channel is wired to the interrupt controller and may be used as event timer, one channel is
     wired to the speaker and used to generate sound tones, and one timer is reserved for platform purposes.

     The attimer driver uses a single hardware channel to provide both time counter and event timer functionality.  To make this possible, the
     respective counter must be running in periodic mode.  As a result, the one-shot event timer mode is supported only when time counter func-
     tionality is disabled.

     The event timer provided by the driver is irrelevant to CPU power states.

SEE ALSO

     apic(4), atrtc(4), eventtimers(4), hpet(4), timecounters(4)

BSD
								   May 26, 2014 							       BSD