Programmable Interval Timer (PIT) definitions. More...

Classes
struct	tvec_base_s
	Contains all the timers of a single CPU. More...

struct	timer_list
	Represents the request to execute a function in the future, also known as timer. More...

Macros
#define	ENABLE_REAL_TIMER_SYSTEM

#define	ITIMER_REAL 0
	Counts down in real (i.e., wall clock) time. More...

#define	ITIMER_VIRTUAL 1
	Counts down against the user-mode CPU time consumed by the process.

#define	ITIMER_PROF 2

#define	TICKS_PER_SECOND 1193
	Number of ticks per seconds.

#define	TVN_COUNT 4
	Number of normal timer vectors.

#define	TVN_BITS 6
	Number of bits for the normal timer vector.

#define	TVR_BITS 8
	Number of bits for the root timer vector.

#define	TVN_SIZE (1 << TVN_BITS)
	Number of headers in a normal timer vector.

#define	TVR_SIZE (1 << TVR_BITS)
	Number of headers in a root timer vector.

#define	TVN_MASK (TVN_SIZE - 1)
	A mask with all 1s for the normal timer vector (0b00111111)

#define	TVR_MASK (TVR_SIZE - 1)
	A mask with all 1s for the root timer vector (0b11111111)

#define	TIMER_TICKS_BITS(tv) (TVR_BITS + TVN_BITS * (tv))
	A shift used to calculate a timer position inside the tvec_base structure.

#define	TIMER_TICKS(tv) (1 << TIMER_TICKS_BITS(tv))
	Expiration ticks of timer based on position inside tvec_base structure.

Typedefs
typedef struct tvec_base_s	tvec_base_t
	Contains all the timers of a single CPU.

Functions
void	timer_handler (pt_regs *f)
	Handles the timer. More...

void	timer_install (void)
	Sets up the system clock by installing the timer handler into IRQ0.

uint64_t	timer_get_seconds (void)
	Returns the number of seconds since the system started its execution. More...

unsigned long	timer_get_ticks (void)
	Returns the number of ticks since the system started its execution. More...

void	timer_phase (const uint32_t hz)
	Allows to set the timer phase to the given frequency. More...

void	dynamic_timers_install (void)
	Initialize dynamic timer system.

void	init_timer (struct timer_list *timer)
	Initializes a new timer struct. More...

void	run_timer_softirq (void)
	Updates the timer data structures.

void	add_timer (struct timer_list *timer)
	Add a new timer to the current CPU. More...

void	remove_timer (struct timer_list *timer)
	Removes a timer from the current CPU. More...

int	sys_nanosleep (const struct timespec req, struct timespec rem)
	Suspends the execution of the calling thread. More...

unsigned	sys_alarm (int seconds)
	Send signal to calling thread after desired seconds. More...

int	sys_getitimer (int which, struct itimerval *curr_value)
	Fills the structure pointed to by curr_value with the current setting for the timer specified by which. More...

int	sys_setitimer (int which, const struct itimerval new_value, struct itimerval old_value)
	Arms or disarms the timer specified by which, by setting the timer to the value specified by new_value. More...

void	update_process_profiling_timer (task_struct *proc)
	Update the profiling timer and generate SIGPROF if it has expired. More...

Detailed Description

Programmable Interval Timer (PIT) definitions.

Copyright: (c) 2014-2024 This file is distributed under the MIT License. See LICENSE.md for details.

Macro Definition Documentation

◆ ENABLE_REAL_TIMER_SYSTEM

#define ENABLE_REAL_TIMER_SYSTEM

This enables the dynamic timer system use an hierarchical timing wheel, an optimized data structure that allows O(1) insertion, O(1) deletion and ammortized O(1) tick update.

◆ ITIMER_PROF

#define ITIMER_PROF 2

This timer counts down against the total (i.e., both user and system) CPU time consumed by the process.

◆ ITIMER_REAL

#define ITIMER_REAL 0

Counts down in real (i.e., wall clock) time.

This enables the system dump tvec_base timer vectors content on the console.

Function Documentation

◆ add_timer()

void add_timer ( struct timer_list * timer )

Add a new timer to the current CPU.

Parameters

timer The timer to add.

◆ init_timer()

void init_timer ( struct timer_list * timer )

Initializes a new timer struct.

Parameters

timer The timer to initialize.

◆ remove_timer()

void remove_timer ( struct timer_list * timer )

Removes a timer from the current CPU.

Parameters

timer The timer to remove.

◆ sys_alarm()

unsigned sys_alarm ( int seconds )

Send signal to calling thread after desired seconds.

Parameters

seconds The number of seconds in the interval

Returns: the number of seconds remaining until any previously scheduled alarm was due to be delivered, or zero if there was no previously scheduled alarm.

◆ sys_getitimer()

int sys_getitimer	(	int	which,
		struct itimerval *	curr_value
	)

Fills the structure pointed to by curr_value with the current setting for the timer specified by which.

Parameters

which	The time domain (i.e., ITIMER_REAL, ITIMER_VIRTUAL, ITIMER_PROF)
curr_value	There the values must be stored.

Returns: Zero on success, or a negative value indicating the error.

◆ sys_nanosleep()

int sys_nanosleep	(	const struct timespec *	req,
		struct timespec *	rem
	)

Suspends the execution of the calling thread.

Parameters

req	The amount of time we want to sleep.
rem	The remaining time we did not sleep.

Returns: If the call is interrupted by a signal handler, nanosleep() returns -1, sets errno to EINTR, and writes the remaining time into the structure pointed to by rem unless rem is NULL.

The execution is suspended until either at least the time specified in *req has elapsed, or the delivery of a signal that triggers the invocation of a handler in the calling thread or that terminates the process.

◆ sys_setitimer()

int sys_setitimer	(	int	which,
		const struct itimerval *	new_value,
		struct itimerval *	old_value
	)

Arms or disarms the timer specified by which, by setting the timer to the value specified by new_value.

The system provides each process with three interval timers, each decrementing in a distinct time domain. When any timer expires, a signal is sent to the process, and the timer (potentially) restarts.

Parameters

which	The time domain (i.e., ITIMER_REAL, ITIMER_VIRTUAL, ITIMER_PROF)
new_value	The new value to set.
old_value	Where the old value must be stored.

Returns: Zero on success, or a negative value indicating the error.

◆ timer_get_seconds()

uint64_t timer_get_seconds ( void )

Returns the number of seconds since the system started its execution.

Returns: Value in seconds.

◆ timer_get_ticks()

unsigned long timer_get_ticks ( void )

Returns the number of ticks since the system started its execution.

Returns: Value in ticks.

◆ timer_handler()

void timer_handler ( pt_regs * f )

Handles the timer.

Parameters

f	The interrupt stack frame.

In this case, it's very simple: We increment the 'timer_ticks' variable every time the timer fires. By default, the timer fires 18.222 times per second. Why 18.222Hz? Some engineer at IBM must've been smoking something funky.

◆ timer_phase()

void timer_phase ( const uint32_t hz )

Allows to set the timer phase to the given frequency.

Parameters

hz	The frequency to set.

◆ update_process_profiling_timer()

void update_process_profiling_timer ( task_struct * proc )

Update the profiling timer and generate SIGPROF if it has expired.

Parameters

proc	The process for which we must update the profiling.

Classes

Macros

Typedefs

Functions

Detailed Description

Macro Definition Documentation

◆ ENABLE_REAL_TIMER_SYSTEM

◆ ITIMER_PROF

◆ ITIMER_REAL

Function Documentation

◆ add_timer()

◆ init_timer()

◆ remove_timer()

◆ sys_alarm()

◆ sys_getitimer()

◆ sys_nanosleep()

◆ sys_setitimer()

◆ timer_get_seconds()

◆ timer_get_ticks()

◆ timer_handler()

◆ timer_phase()

◆ update_process_profiling_timer()