minix/kernel/clock.c
2005-04-21 14:53:53 +00:00

362 lines
13 KiB
C
Executable file

/* The file contais the clock task, which handles all time related functions.
* Important events that are handled by the CLOCK include alarm timers and
* (re)scheduling user processes.
* The CLOCK offers a direct interface to kernel processes. System services
* can access its services through system calls, such as sys_syncalrm(). The
* CLOCK task thus is hidden for the outside.
*
* Changes:
* Mar 18, 2004 clock interface moved to SYSTEM task (Jorrit N. Herder)
* Oct 10, 2004 call vector + return values allowed (Jorrit N. Herder)
* Sep 30, 2004 source code documentation updated (Jorrit N. Herder)
* Sep 24, 2004 redesigned timers and alarms (Jorrit N. Herder)
* Jun 04, 2004 new timeout flag alarm functionality (Jorrit N. Herder)
*
* The function do_clocktick() is not triggered from the clock library, but
* by the clock's interrupt handler when a watchdog timer has expired or
* another user process must be scheduled.
*
* In addition to the main clock_task() entry point, which starts the main
* loop, there are several other minor entry points:
* clock_stop: called just before MINIX shutdown
* get_uptime: get realtime since boot in clock ticks
* set_timer: set a watchdog timer (*, see note below!)
* reset_timer: reset a watchdog timer (*)
* calc_elapsed: do timing measurements: get delta ticks and pulses
* read_clock: read the counter of channel 0 of the 8253A timer
*
* (*) The CLOCK task keeps tracks of watchdog timers for the entire kernel.
* The watchdog functions of expired timers are executed in do_clocktick().
* It is crucial that watchdog functions cannot block, or the CLOCK task may
* be blocked. Do not send() a message when the receiver is not expecting it.
* The use of notify(), which always returns, is strictly preferred!
*/
#include "kernel.h"
#include "proc.h"
#include <signal.h>
#include <minix/com.h>
/* Function prototype for PRIVATE functions. */
FORWARD _PROTOTYPE( void init_clock, (void) );
FORWARD _PROTOTYPE( int clock_handler, (irq_hook_t *hook) );
FORWARD _PROTOTYPE( int do_clocktick, (message *m_ptr) );
/* Constant definitions. */
#define SCHED_RATE (MILLISEC*HZ/1000) /* number of ticks per schedule */
#define MILLISEC 100 /* how often to call the scheduler */
/* Clock parameters. */
#if (CHIP == INTEL)
#define COUNTER_FREQ (2*TIMER_FREQ) /* counter frequency using square wave */
#define LATCH_COUNT 0x00 /* cc00xxxx, c = channel, x = any */
#define SQUARE_WAVE 0x36 /* ccaammmb, a = access, m = mode, b = BCD */
/* 11x11, 11 = LSB then MSB, x11 = sq wave */
#define TIMER_COUNT ((unsigned) (TIMER_FREQ/HZ)) /* initial value for counter*/
#define TIMER_FREQ 1193182L /* clock frequency for timer in PC and AT */
#define CLOCK_ACK_BIT 0x80 /* PS/2 clock interrupt acknowledge bit */
#endif
#if (CHIP == M68000)
#define TIMER_FREQ 2457600L /* timer 3 input clock frequency */
#endif
/* The CLOCK's timers queue. The functions in <timers.h> operate on this.
* The process structure contains one timer per type of alarm (SIGNALRM,
* SYNCALRM, and FLAGALRM), which means that a process can have a single
* outstanding timer for each alarm type.
* If other kernel parts want to use additional timers, they must declare
* their own persistent timer structure, which can be passed to the clock
* via (re)set_timer().
* When a timer expires its watchdog function is run by the CLOCK task.
*/
PRIVATE timer_t *clock_timers; /* queue of CLOCK timers */
PRIVATE clock_t next_timeout; /* realtime that next timer expires */
/* The boot time and the current real time. The real time is incremented by
* the clock on each clock tick. The boot time is set by a utility program
* after system startup to prevent troubles reading the CMOS.
*/
PRIVATE clock_t realtime; /* real time clock */
/* Variables changed by interrupt handler. */
PRIVATE clock_t pending_ticks; /* ticks seen by low level only */
PRIVATE int sched_ticks = SCHED_RATE; /* counter: when 0, call scheduler */
PRIVATE struct proc *prev_ptr; /* last user process run by clock */
/*===========================================================================*
* clock_task *
*===========================================================================*/
PUBLIC void clock_task()
{
/* Main program of clock task. It corrects realtime by adding pending ticks
* seen only by the interrupt service, then it determines which call this is
* by looking at the message type and dispatches.
*/
message m; /* message buffer for both input and output */
int result;
init_clock(); /* initialize clock task */
/* Main loop of the clock task. Get work, process it, sometimes reply. */
while (TRUE) {
/* Go get a message. */
receive(ANY, &m);
/* Transfer ticks seen by the low level handler. */
lock();
realtime += pending_ticks;
pending_ticks = 0;
unlock();
/* Handle the request. */
switch (m.m_type) {
case HARD_INT:
result = do_clocktick(&m); /* handle clock tick */
break;
default: /* illegal message type */
kprintf("CLOCK got illegal request from %d.\n", m.m_source);
result = EBADREQUEST;
}
/* Send reply, unless inhibited, e.g. by do_clocktick(). */
if (result != EDONTREPLY) {
m.m_type = result;
send(m.m_source, &m);
}
}
}
/*===========================================================================*
* do_clocktick *
*===========================================================================*/
PRIVATE int do_clocktick(m_ptr)
message *m_ptr; /* pointer to request message */
{
/* Despite its name, this routine is not called on every clock tick. It
* is called on those clock ticks when a lot of work needs to be done.
*/
register struct proc *rp;
register int proc_nr;
timer_t *tp;
struct proc *p;
/* Check if a clock timer expired and run its watchdog function. */
if (next_timeout <= realtime) {
tmrs_exptimers(&clock_timers, realtime);
next_timeout = clock_timers == NULL ?
TMR_NEVER : clock_timers->tmr_exp_time;
}
/* If a user process has been running too long, pick another one. */
if (--sched_ticks == 0) {
if (bill_ptr == prev_ptr) lock_sched(); /* process has run too long */
sched_ticks = SCHED_RATE; /* reset quantum */
prev_ptr = bill_ptr; /* new previous process */
}
/* Inhibit sending a reply. */
return(EDONTREPLY);
}
/*===========================================================================*
* clock_handler *
*===========================================================================*/
PRIVATE int clock_handler(hook)
irq_hook_t *hook;
{
/* This executes on every clock tick (i.e., every time the timer chip
* generates an interrupt). It does a little bit of work so the clock
* task does not have to be called on every tick.
*
* Switch context to do_clocktick() if an alarm has gone off.
* Also switch there to reschedule if the reschedule will do something.
* This happens when
* (1) quantum has expired
* (2) current process received full quantum (as clock sampled it!)
* (3) something else is ready to run.
*
* Many global global and static variables are accessed here. The safety
* of this must be justified. Most of them are not changed here:
* k_reenter:
* This safely tells if the clock interrupt is nested.
* proc_ptr, bill_ptr:
* These are used for accounting. It does not matter if proc.c
* is changing them, provided they are always valid pointers,
* since at worst the previous process would be billed.
* next_timeout, realtime, sched_ticks, bill_ptr, prev_ptr
* rdy_head[PPRI_USER]
* These are tested to decide whether to call notify(). It
* does not matter if the test is sometimes (rarely) backwards
* due to a race, since this will only delay the high-level
* processing by one tick, or call the high level unnecessarily.
* The variables which are changed require more care:
* rp->user_time, rp->sys_time:
* These are protected by explicit locks in system.c. They are
* not properly protected in dmp.c (the increment here is not
* atomic) but that hardly matters.
* pending_ticks:
* This is protected by explicit locks in clock.c. Don't
* update realtime directly, since there are too many
* references to it to guard conveniently.
* lost_ticks:
* Clock ticks counted outside the clock task.
* sched_ticks, prev_ptr:
* Updating these competes with similar code in do_clocktick().
* No lock is necessary, because if bad things happen here
* (like sched_ticks going negative), the code in do_clocktick()
* will restore the variables to reasonable values, and an
* occasional missed or extra sched() is harmless.
*
* Are these complications worth the trouble? Well, they make the system 15%
* faster on a 5MHz 8088, and make task debugging much easier since there are
* no task switches on an inactive system.
*/
register struct proc *rp;
register unsigned ticks;
clock_t now;
/* Acknowledge the PS/2 clock interrupt. */
if (ps_mca) outb(PORT_B, inb(PORT_B) | CLOCK_ACK_BIT);
/* Update user and system accounting times. Charge the current process for
* user time. If the current process is not billable, that is, if a non-user
* process is running, charge the billable process for system time as well.
* Thus the unbillable process' user time is the billable user's system time.
*/
ticks = lost_ticks + 1;
lost_ticks = 0;
pending_ticks += ticks;
now = realtime + pending_ticks;
rp = (k_reenter == 0) ? proc_ptr : proc_addr(HARDWARE);
rp->user_time += ticks;
if (rp != bill_ptr && rp != proc_addr(IDLE)) bill_ptr->sys_time += ticks;
/* Check if do_clocktick() must be called. Done for alarms and scheduling.
* If bill_ptr == prev_ptr, there are no ready users so don't need sched().
*/
if (next_timeout <= now || (sched_ticks == 1 && bill_ptr == prev_ptr
&& rdy_head[PPRI_USER] != NIL_PROC))
{
notify(CLOCK, HARD_INT);
}
else if (--sched_ticks == 0) {
sched_ticks = SCHED_RATE; /* reset quantum */
prev_ptr = bill_ptr; /* new previous process */
}
return 1; /* reenable clock interrupts */
}
/*===========================================================================*
* get_uptime *
*===========================================================================*/
PUBLIC clock_t get_uptime()
{
/* Get and return the current clock uptime in ticks.
* Be careful about pending_ticks.
*/
clock_t uptime;
lock();
uptime = realtime + pending_ticks;
unlock();
return(uptime);
}
/*===========================================================================*
* set_timer *
*===========================================================================*/
PUBLIC void set_timer(tp, exp_time, watchdog)
struct timer *tp; /* pointer to timer structure */
clock_t exp_time; /* expiration realtime */
tmr_func_t watchdog; /* watchdog to be called */
{
/* Insert the new timer in the active timers list. Always update the
* next timeout time by setting it to the front of the active list.
*/
tmrs_settimer(&clock_timers, tp, exp_time, watchdog);
next_timeout = clock_timers->tmr_exp_time;
}
/*===========================================================================*
* reset_timer *
*===========================================================================*/
PUBLIC void reset_timer(tp)
struct timer *tp; /* pointer to timer structure */
{
/* The timer pointed to by 'tp' is no longer needed. Remove it from both the
* active and expired lists. Always update the next timeout time by setting
* it to the front of the active list.
*/
tmrs_clrtimer(&clock_timers, tp);
next_timeout = (clock_timers == NULL) ?
TMR_NEVER : clock_timers->tmr_exp_time;
}
#if (CHIP == INTEL)
/*===========================================================================*
* init_clock *
*===========================================================================*/
PRIVATE void init_clock()
{
/* Initialize channel 0 of the 8253A timer to, e.g., 60 Hz. */
static irq_hook_t clock_hook;
outb(TIMER_MODE, SQUARE_WAVE); /* set timer to run continuously */
outb(TIMER0, TIMER_COUNT); /* load timer low byte */
outb(TIMER0, TIMER_COUNT >> 8); /* load timer high byte */
put_irq_handler(&clock_hook, CLOCK_IRQ, clock_handler);/* register handler */
enable_irq(&clock_hook); /* ready for clock interrupts */
}
/*===========================================================================*
* clock_stop *
*===========================================================================*/
PUBLIC void clock_stop()
{
/* Reset the clock to the BIOS rate. (For rebooting) */
outb(TIMER_MODE, 0x36);
outb(TIMER0, 0);
outb(TIMER0, 0);
}
/*===========================================================================*
* read_clock *
*===========================================================================*/
PUBLIC unsigned long read_clock()
{
/* Read the counter of channel 0 of the 8253A timer. This counter counts
* down at a rate of TIMER_FREQ and restarts at TIMER_COUNT-1 when it
* reaches zero. A hardware interrupt (clock tick) occurs when the counter
* gets to zero and restarts its cycle.
*/
unsigned count;
lock();
outb(TIMER_MODE, LATCH_COUNT);
count = inb(TIMER0);
count |= (inb(TIMER0) << 8);
unlock();
return count;
}
#endif /* (CHIP == INTEL) */
#if (CHIP == M68000)
/* Initialize the timer C in the MFP 68901: implement init_clock() here. */
#endif /* (CHIP == M68000) */