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acpi_hpet(4) [freebsd 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

Check Out this Related Man Page

EVENTTIMERS(9)						   BSD Kernel Developer's Manual					    EVENTTIMERS(9)

eventtimers -- kernel event timers subsystem SYNOPSIS
#include <sys/timeet.h> struct eventtimer; typedef int et_start_t(struct eventtimer *et, sbintime_t first, sbintime_t period); typedef int et_stop_t(struct eventtimer *et); typedef void et_event_cb_t(struct eventtimer *et, void *arg); typedef int et_deregister_cb_t(struct eventtimer *et, void *arg); struct eventtimer { SLIST_ENTRY(eventtimer) et_all; char *et_name; int et_flags; #define ET_FLAGS_PERIODIC 1 #define ET_FLAGS_ONESHOT 2 #define ET_FLAGS_PERCPU 4 #define ET_FLAGS_C3STOP 8 #define ET_FLAGS_POW2DIV 16 int et_quality; int et_active; uint64_t et_frequency; sbintime_t et_min_period; sbintime_t et_max_period; et_start_t *et_start; et_stop_t *et_stop; et_event_cb_t *et_event_cb; et_deregister_cb_t *et_deregister_cb; void *et_arg; void *et_priv; struct sysctl_oid *et_sysctl; }; int et_register(struct eventtimer *et); int et_deregister(struct eventtimer *et); void et_change_frequency(struct eventtimer *et, uint64_t newfreq); ET_LOCK(); ET_UNLOCK(); struct eventtimer * et_find(const char *name, int check, int want); int et_init(struct eventtimer *et, et_event_cb_t *event, et_deregister_cb_t *deregister, void *arg); int et_start(struct eventtimer *et, sbintime_t first, sbintime_t period); int et_stop(struct eventtimer *et); int et_ban(struct eventtimer *et); int et_free(struct eventtimer *et); DESCRIPTION
Event timers are responsible for generating interrupts at specified time or periodically, to run different time-based events. Subsystem con- sists of three main parts: Drivers Manage hardware to generate requested time events. Consumers sys/kern/kern_clocksource.c uses event timers to supply kernel with hardclock(), statclock() and profclock() time events. Glue code sys/sys/timeet.h, sys/kern/kern_et.c provide APIs for event timer drivers and consumers. DRIVER API
Driver API is built around eventtimer structure. To register its functionality driver allocates that structure and calls et_register(). Driver should fill following fields there: et_name Unique name of the event timer for management purposes. et_flags Set of flags, describing timer capabilities: ET_FLAGS_PERIODIC Periodic mode supported. ET_FLAGS_ONESHOT One-shot mode supported. ET_FLAGS_PERCPU Timer is per-CPU. ET_FLAGS_C3STOP Timer may stop in CPU sleep state. ET_FLAGS_POW2DIV Timer supports only 2^n divisors. et_quality Abstract value to certify whether this timecounter is better than the others. Higher value means better. et_frequency Timer oscillator's base frequency, if applicable and known. Used by consumers to predict set of possible frequencies that could be obtained by dividing it. Should be zero if not applicable or unknown. et_min_period, et_max_period Minimal and maximal reliably programmable time periods. et_start Driver's timer start function pointer. et_stop Driver's timer stop function pointer. et_priv Driver's private data storage. After the event timer functionality is registered, it is controlled via et_start and et_stop methods. et_start method is called to start the specified event timer. The last two arguments are used to specify time when events should be generated. first argument specifies time period before the first event generated. In periodic mode NULL value specifies that first period is equal to the period argument value. period argument specifies the time period between following events for the periodic mode. The NULL value there specifies the one-shot mode. At least one of these two arguments should be not NULL. When event time arrive, driver should call et_event_cb callback function, passing et_arg as the second argument. et_stop method is called to stop the specified event timer. For the per-CPU event timers et_start and et_stop methods control timers associated with the current CPU. Driver may deregister its functionality by calling et_deregister(). If the frequency of the clock hardware can change while it is running (for example, during power-saving modes), the driver must call et_change_frequency() on each change. If the given event timer is the active timer, et_change_frequency() stops the timer on all CPUs, updates et->frequency, then restarts the timer on all CPUs so that all current events are rescheduled using the new frequency. If the given timer is not currently active, et_change_frequency() simply updates et->frequency. CONSUMER API
et_find() allows consumer to find available event timer, optionally matching specific name and/or capability flags. Consumer may read returned eventtimer structure, but should not modify it. When wanted event timer is found, et_init() should be called for it, submitting event and optionally deregister callbacks functions, and the opaque argument arg. That argument will be passed as argument to the callbacks. Event callback function will be called on scheduled time events. It is called from the hardware interrupt context, so no sleep is permitted there. Deregister callback function may be called to report consumer that the event timer functionality is no longer available. On this call, consumer should stop using event timer before the return. After the timer is found and initialized, it can be controlled via et_start() and et_stop(). The arguments are the same as described in driver API. Per-CPU event timers can be controlled only from specific CPUs. et_ban() allows consumer to mark event timer as broken via clearing both one-shot and periodic capability flags, if it was somehow detected. et_free() is the opposite to et_init(). It releases the event timer for other consumers use. ET_LOCK() and ET_UNLOCK() macros should be used to manage mutex(9) lock around et_find(), et_init() and et_free() calls to serialize access to the list of the registered event timers and the pointers returned by et_find(). et_start() and et_stop() calls should be serialized in consumer's internal way to avoid concurrent timer hardware access. SEE ALSO
eventtimers(4) AUTHORS
Alexander Motin <> BSD
April 2, 2014 BSD

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