HPET Namespace Reference

Abstraction of the HPET existing in "modern" computers (since ~2005) More...

Classes
struct	ConfigurationRegister.__unnamed44__

Typedefs
typedef uint64_t	InterruptStatusRegister
	Global state register for interrupts. More...

Enumerations
enum	RegisterOffset : uint16_t {   CAPABILITIES_AND_ID = 0x000 ,   CONFIGURATION = 0x010 ,   INTERRUPT_STATUS = 0x020 ,   MAIN_COUNTER = 0x0f0 }
	Register Offsets. More...
enum	CounterSize {   SIZE_32BIT = 0x0 ,   SIZE_64BIT = 0x1 }
	Size of the global counter and the comparators.

Functions
bool	init ()
	Initializes the HPET system from ACPI Table. More...
void	delay (uint64_t usecs)
	Delays the caller's execution by approx. More...
bool	isEnabled ()
	Checks whether the HPET system is enabled. More...
void	reset ()
	Reset the global counter to zero. More...
uint64_t	get ()
void	enable ()
	Activate the HPET system. More...
void	disable ()
	Deactivate the HPET system. More...
size_t	countComparators ()
	Retrieve the number of HPET comparators. More...
Comparator *	getComparator (size_t n)
	Returns a pointer to the nth timer comparator. More...

Constants
uintptr_t	base_address = 0

Detailed Description

Abstraction of the HPET existing in "modern" computers (since ~2005)

Today's systems contain, in addition to the old Programmable Interval Timer (PIT), several additional timers, the "High Precision Event Timers" (HPET). Those timers, developed by Intel and Microsoft, are intended as replacement for both the PIT and the CMOS Real Time Clock in the long run.

Unlike the PIT, the HPETs are in a well-define state at system boot, are configured via Memory Mapped IO, have a significantly higher precision, and support up to 256 independent comparators (depending on the architecture).

The HPET timers are implemented using a single counter and several comparators. The counter increments at a fixed frequency that is independent of the CPUs current frequency (which might change due to CPU power management). The only cause for reading a value smaller than previous values is a intermittent counter overflow.

After system boot, the HPET is in the following state:

1. The global counter is set to 0 and stopped.
2. The comparators' value registers are set to their maximum value.
3. All interrupts are disabled:
   • The global activation bit is 0.
   • Every comparators' interrupt-enable bit is set to 0
   • The legacy mode is disabled

See also

IA-PC HPET (High Precision Event Timers) Specification 1.0a

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Class Documentation

HPET::ConfigurationRegister.__unnamed44__

struct HPET::ConfigurationRegister.__unnamed44__

Class Members
uint64_t	enabled: 1	Enables/disables the HPET.
uint64_t	legacy_routing: 1	if 1, legacy routing is enabled
uint64_t	__pad0__: 62

Typedef Documentation

InterruptStatusRegister

typedef uint64_t HPET::InterruptStatusRegister

Global state register for interrupts.

This register is only required for level-triggered interrupts – it provides information about the comparator that issued an interrupt. To acknowledge the interrupt, the software is required to write 1 to the corresponding bit (writes of 0 have no effect).

For edge-triggered interrupts, the corresponding bit is always set to 0 and should be ignored.

See also

IA-PC HPET - 2.3.6 General Interrupt Status Register

Enumeration Type Documentation

RegisterOffset

enum HPET::RegisterOffset : uint16_t

Register Offsets.

See also

IA-PC HPET - 2.3.1 Register Overview

Enumerator
CAPABILITIES_AND_ID	CapabilitiesAndIdRegister
CONFIGURATION	ConfigurationRegister
INTERRUPT_STATUS	InterruptStatusRegister
MAIN_COUNTER	global counter

Function Documentation

init()

bool HPET::init

(

)

Initializes the HPET system from ACPI Table.

Returns

true on success, false on error

delay()

void HPET::delay

(

uint64_t

usecs

)

Delays the caller's execution by approx.

Actively waits by polling the main counter until at least the given micro seconds have passed

Parameters

usecs

time to wait in micro seconds.

isEnabled()

bool HPET::isEnabled

(

)

Checks whether the HPET system is enabled.

Checks whether the HPET system is activated globally, i.e. the global counter is running and the comparators could send interrupts (if configured to do so).

Returns

true if enabled, false if disabled

reset()

void HPET::reset

(

)

Reset the global counter to zero.

See also

IA-PC HPET - 2.3.7 Main Counter Register

enable()

void HPET::enable

(

)

Activate the HPET system.

Activate the HPET system globally by enabling the global counter and, thereby, enabling all (previously configured) interrupts.

disable()

void HPET::disable

(

)

Deactivate the HPET system.

Deactivates the HPET system globally by disabling the global counter and, thereby, disabling all interrupts.

countComparators()

size_t HPET::countComparators

(

)

Retrieve the number of HPET comparators.

Returns

number of comparators.

getComparator()

Comparator * HPET::getComparator

(

size_t

n

)

Returns a pointer to the nth timer comparator.

Returns

A pointer to the timer comperator, or nullptr if invalid timer.