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attimer(4) [freebsd man page]

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

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

Check Out this Related Man Page

HPET(4) 						   BSD Kernel Interfaces Manual 						   HPET(4)

hpet -- High Precision Event Timer driver SYNOPSIS
To compile this driver into the kernel, place the following lines in your kernel configuration file: device acpi The following tunables are settable from the loader(8): hint.hpet.X.allowed_irqs is a 32bit mask. Each set bit allows driver to use respective IRQ, if BIOS also set respective capability bit in comparator's configuration register. Default value is 0xffff0000, except some known broken hardware. hint.hpet.X.clock controls event timers functionality support. Setting to 0, disables it. Default value is 1. hint.hpet.X.legacy_route controls "LegacyReplacement Route" mode. If enabled, HPET will steal IRQ0 of i8254 timer and IRQ8 of RTC. Before using it, make sure that respective drivers are not using interrupts, by setting also: hint.attimer.0.clock=0 hint.atrtc.0.clock=0 Default value is 0. hint.hpet.X.per_cpu controls how much per-CPU event timers should driver attempt to register. This functionality requires every comparator in a group to have own unshared IRQ, so it depends on hardware capabilities and interrupts configuration. Default value is 1. DESCRIPTION
This driver uses High Precision Event Timer hardware (part of the chipset, usually enumerated via ACPI) to supply kernel with one time counter and several (usually from 3 to 8) event timers. This hardware includes single main counter with known increment frequency (10MHz or more), and several programmable comparators (optionally with automatic reload feature). When value of the main counter matches current value of any comparator, interrupt can be generated. Depending on hardware capabilities and configuration, interrupt can be delivered as regular I/O APIC interrupt (ISA or PCI) in range from 0 to 31, or as Front Side Bus interrupt, alike to PCI MSI interrupts, or in so called "Lega- cyReplacement Route" HPET can steal IRQ0 of i8254 and IRQ8 of the RTC. Interrupt can be either edge- or level-triggered. In last case they could be safely shared with PCI IRQs. Driver prefers to use FSB interrupts, if supported, to avoid sharing. If it is not possible, it uses single sharable IRQ from PCI range. Other modes (LegacyReplacement and ISA IRQs) require special care to setup, but could be configured man- ually via device hints. Event timers provided by the driver support both one-shot an periodic modes and irrelevant to CPU power states. Depending on hardware capabilities and configuration, driver can expose each comparator as separate event timer or group them into one or several per-CPU event timers. In last case interrupt of every of those comparators within group is bound to specific CPU core. This is possi- ble only when each of these comparators has own unsharable IRQ. SEE ALSO
acpi(4), apic(4), atrtc(4), attimer(4), eventtimers(4), timecounters(4) HISTORY
The hpet driver first appeared in FreeBSD 6.3. Support for event timers was added in FreeBSD 9.0. BSD
September 14, 2010 BSD

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