Timers

Description

Data Structures
struct	TimerEntry_t
	Description of one sleep request. More...

Macros
#define	IS_PERIODIC(interval)   (((interval) >> 31) == 1)
	Determine if interval in sleep entry is periodic or not.
#define	GET_SLEEPTIME(interval)   ((interval) & (~(1 << 31)))
	Get how long the sleep should take.

Functions
int	os_usleep (unsigned microseconds)
	Kernel implementation of usleep() syscall.
int	os_setitimer (unsigned microseconds)
	Kernel implementation of setitimer() syscall.
void	os_timer_init ()
	This routine initializes kernel scheduling subsystem.
bool	os_schedule_timer (unsigned *delay)
	Provide information on next scheduled event.
void	os_run_timer (uint32_t microtime)
	Fire scheduled event.
static int	do_set_timed_event (unsigned slot, unsigned interval, bool _periodic)
	Perform heavy lifting of setting timers This routine will store timed event into list of timed events.
static int	set_timed_event (unsigned microseconds, bool periodic)
	Find a slot for timed event and store it.
static int	cancel_timed_event (Thread_t owner, bool periodic)
	Cancels existing timed event.
static void	delay_us (uint32_t period_us)
	Perform short busy wait.
static uint32_t	get_sleep_time (uint32_t sleep_from, uint32_t microtime)
	Helper function to calculate time considering type wraparound.

Variables
struct TimerEntry_t	sleepers [SLEEPERS_MAX]
	List of all delays requested from kernel.

Macro Definition Documentation

GET_SLEEPTIME

#define GET_SLEEPTIME

(

interval

)

((interval) & (~(1 << 31)))

Get how long the sleep should take.

Will clean the periodicity flag from interval.

Returns

sleep time in microseconds.

IS_PERIODIC

#define IS_PERIODIC

(

interval

)

(((interval) >> 31) == 1)

Determine if interval in sleep entry is periodic or not.

Returns

1 if interval is periodic, 0 if interval is one-shot.

Function Documentation

cancel_timed_event()

static int cancel_timed_event ( Thread_t  owner, bool  periodic  )

static

Cancels existing timed event.

This function is only accessible for periodic timers externally. It allows cancelling of interval timers set previously.

Parameters

owner	thread which shall own the interval timer
periodic	true if periodic timer of given thread should be cancelled

Returns

0 if operation performed succesfully.

delay_us()

static void delay_us ( uint32_t  period_us )

static

Perform short busy wait.

This will perform busywait in the context of current thread. Useful to do short waits for I/O.

Parameters

period_us

how long the wait should take

do_set_timed_event()

static int do_set_timed_event ( unsigned  slot, unsigned  interval, bool  _periodic  )

static

Perform heavy lifting of setting timers This routine will store timed event into list of timed events.

If event is not periodic, it will also stop thread (os_usleep semantics).

Parameters

slot	number of slot in sleepers list
interval	amount of us for which thread should sleep
_periodic	true if timer should be periodic, false otherwise

Returns

0 if timer was set up properly

get_sleep_time()

static uint32_t get_sleep_time ( uint32_t  sleep_from, uint32_t  microtime  )

static

Helper function to calculate time considering type wraparound.

This function will calculate the final time considering timer wraparound.

Parameters

sleep_from	time at which the sleep starts (microseconds)
microtime	duration of sleep (microseconds)

Returns

new value of kernel timer at the end of sleep

os_run_timer()

void os_run_timer

(

uint32_t

microtime

)

Fire scheduled event.

Will find and run scheduled event.

Parameters

microtime

current processor time in microseconds

os_schedule_timer()

bool os_schedule_timer

(

unsigned *

delay

)

Provide information on next scheduled event.

This function informs caller about delay until next scheduled event. Next scheduled event may be either wake-up of sleeped thread, or interval timer.

Parameters

[out]

delay

address of buffer, where delay to next scheduled event will be written

Returns

true if there is any scheduled event known and at address pointed to by delay value was written. Returns false if there is no known scheduled event. In such case content of memory pointed to by delay is undefined.

os_setitimer()

int os_setitimer

(

unsigned

microseconds

)

Kernel implementation of setitimer() syscall.

See setitimer for details on arguments.

os_timer_init()

void os_timer_init

(

)

This routine initializes kernel scheduling subsystem.

It is necessary to call this routine before first call to either timer syscalls, or os_run_timer otherwise things will go wrong.

os_usleep()

int os_usleep

(

unsigned

microseconds

)

Kernel implementation of usleep() syscall.

See usleep for details on arguments.

set_timed_event()

static int set_timed_event ( unsigned  microseconds, bool  periodic  )

static

Find a slot for timed event and store it.

This is actual execution core for both os_usleep and os_setitimer functions. It will find free slot or slot already occupied by calling thread and will set / update timeout values.

Parameters

microseconds	time for which thread should sleep / wait for event
periodic	true if this event is periodic

Returns

error status. 0 means no error.

Variable Documentation

sleepers

struct TimerEntry_t sleepers[SLEEPERS_MAX]

List of all delays requested from kernel.

This structure contains all scheduled sleeps requested by all threads. Every thread can technically request one periodic timer and one one-shot delay.