310 lines
12 KiB
C
Executable file
310 lines
12 KiB
C
Executable file
/* This file contains the clock task, which handles time related functions.
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* Important events that are handled by the CLOCK include setting and
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* monitoring alarm timers and deciding when to (re)schedule processes.
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* The CLOCK offers a direct interface to kernel processes. System services
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* can access its services through system calls, such as sys_setalarm(). The
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* CLOCK task thus is hidden from the outside world.
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*
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* Changes:
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* Oct 08, 2005 reordering and comment editing (A. S. Woodhull)
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* Mar 18, 2004 clock interface moved to SYSTEM task (Jorrit N. Herder)
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* Sep 30, 2004 source code documentation updated (Jorrit N. Herder)
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* Sep 24, 2004 redesigned alarm timers (Jorrit N. Herder)
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*
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* The function do_clocktick() is triggered by the clock's interrupt
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* handler when a watchdog timer has expired or a process must be scheduled.
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*
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* In addition to the main clock_task() entry point, which starts the main
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* loop, there are several other minor entry points:
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* clock_stop: called just before MINIX shutdown
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* get_uptime: get realtime since boot in clock ticks
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* set_timer: set a watchdog timer (+)
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* reset_timer: reset a watchdog timer (+)
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* read_clock: read the counter of channel 0 of the 8253A timer
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*
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* (+) The CLOCK task keeps tracks of watchdog timers for the entire kernel.
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* The watchdog functions of expired timers are executed in do_clocktick().
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* It is crucial that watchdog functions not block, or the CLOCK task may
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* be blocked. Do not send() a message when the receiver is not expecting it.
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* Instead, notify(), which always returns, should be used.
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*/
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#include "kernel.h"
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#include "proc.h"
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#include <signal.h>
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#include <minix/com.h>
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/* Function prototype for PRIVATE functions. */
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FORWARD _PROTOTYPE( void init_clock, (void) );
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FORWARD _PROTOTYPE( int clock_handler, (irq_hook_t *hook) );
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FORWARD _PROTOTYPE( int do_clocktick, (message *m_ptr) );
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FORWARD _PROTOTYPE( void load_update, (void));
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/* Clock parameters. */
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#define COUNTER_FREQ (2*TIMER_FREQ) /* counter frequency using square wave */
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#define LATCH_COUNT 0x00 /* cc00xxxx, c = channel, x = any */
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#define SQUARE_WAVE 0x36 /* ccaammmb, a = access, m = mode, b = BCD */
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/* 11x11, 11 = LSB then MSB, x11 = sq wave */
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#define TIMER_COUNT ((unsigned) (TIMER_FREQ/HZ)) /* initial value for counter*/
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#define TIMER_FREQ 1193182L /* clock frequency for timer in PC and AT */
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#define CLOCK_ACK_BIT 0x80 /* PS/2 clock interrupt acknowledge bit */
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/* The CLOCK's timers queue. The functions in <timers.h> operate on this.
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* Each system process possesses a single synchronous alarm timer. If other
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* kernel parts want to use additional timers, they must declare their own
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* persistent (static) timer structure, which can be passed to the clock
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* via (re)set_timer().
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* When a timer expires its watchdog function is run by the CLOCK task.
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*/
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PRIVATE timer_t *clock_timers; /* queue of CLOCK timers */
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PRIVATE clock_t next_timeout; /* realtime that next timer expires */
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/* The time is incremented by the interrupt handler on each clock tick. */
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PRIVATE clock_t realtime; /* real time clock */
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PRIVATE irq_hook_t clock_hook; /* interrupt handler hook */
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/*===========================================================================*
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* clock_task *
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*===========================================================================*/
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PUBLIC void clock_task()
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{
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/* Main program of clock task. If the call is not HARD_INT it is an error.
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*/
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message m; /* message buffer for both input and output */
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int result; /* result returned by the handler */
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init_clock(); /* initialize clock task */
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/* Main loop of the clock task. Get work, process it. Never reply. */
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while (TRUE) {
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/* Go get a message. */
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receive(ANY, &m);
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/* Handle the request. Only clock ticks are expected. */
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switch (m.m_type) {
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case HARD_INT:
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result = do_clocktick(&m); /* handle clock tick */
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break;
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default: /* illegal request type */
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kprintf("CLOCK: illegal request %d from %d.\n", m.m_type,m.m_source);
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}
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}
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}
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/*===========================================================================*
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* do_clocktick *
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*===========================================================================*/
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PRIVATE int do_clocktick(m_ptr)
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message *m_ptr; /* pointer to request message */
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{
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/* Despite its name, this routine is not called on every clock tick. It
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* is called on those clock ticks when a lot of work needs to be done.
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*/
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/* A process used up a full quantum. The interrupt handler stored this
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* process in 'prev_ptr'. First make sure that the process is not on the
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* scheduling queues. Then announce the process ready again. Since it has
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* no more time left, it gets a new quantum and is inserted at the right
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* place in the queues. As a side-effect a new process will be scheduled.
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*/
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if (prev_ptr->p_ticks_left <= 0 && priv(prev_ptr)->s_flags & PREEMPTIBLE) {
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lock_dequeue(prev_ptr); /* take it off the queues */
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lock_enqueue(prev_ptr); /* and reinsert it again */
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}
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/* Check if a clock timer expired and run its watchdog function. */
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if (next_timeout <= realtime) {
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tmrs_exptimers(&clock_timers, realtime, NULL);
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next_timeout = clock_timers == NULL ?
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TMR_NEVER : clock_timers->tmr_exp_time;
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}
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/* Inhibit sending a reply. */
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return(EDONTREPLY);
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}
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/*===========================================================================*
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* init_clock *
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*===========================================================================*/
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PRIVATE void init_clock()
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{
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/* Initialize the CLOCK's interrupt hook. */
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clock_hook.proc_nr_e = CLOCK;
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/* Initialize channel 0 of the 8253A timer to, e.g., 60 Hz, and register
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* the CLOCK task's interrupt handler to be run on every clock tick.
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*/
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outb(TIMER_MODE, SQUARE_WAVE); /* set timer to run continuously */
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outb(TIMER0, TIMER_COUNT); /* load timer low byte */
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outb(TIMER0, TIMER_COUNT >> 8); /* load timer high byte */
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put_irq_handler(&clock_hook, CLOCK_IRQ, clock_handler);
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enable_irq(&clock_hook); /* ready for clock interrupts */
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/* Set a watchdog timer to periodically balance the scheduling queues. */
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balance_queues(NULL); /* side-effect sets new timer */
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}
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/*===========================================================================*
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* clock_stop *
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*===========================================================================*/
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PUBLIC void clock_stop()
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{
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/* Reset the clock to the BIOS rate. (For rebooting.) */
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outb(TIMER_MODE, 0x36);
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outb(TIMER0, 0);
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outb(TIMER0, 0);
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}
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/*===========================================================================*
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* clock_handler *
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*===========================================================================*/
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PRIVATE int clock_handler(hook)
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irq_hook_t *hook;
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{
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/* This executes on each clock tick (i.e., every time the timer chip generates
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* an interrupt). It does a little bit of work so the clock task does not have
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* to be called on every tick. The clock task is called when:
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*
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* (1) the scheduling quantum of the running process has expired, or
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* (2) a timer has expired and the watchdog function should be run.
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*
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* Many global global and static variables are accessed here. The safety of
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* this must be justified. All scheduling and message passing code acquires a
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* lock by temporarily disabling interrupts, so no conflicts with calls from
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* the task level can occur. Furthermore, interrupts are not reentrant, the
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* interrupt handler cannot be bothered by other interrupts.
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*
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* Variables that are updated in the clock's interrupt handler:
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* lost_ticks:
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* Clock ticks counted outside the clock task. This for example
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* is used when the boot monitor processes a real mode interrupt.
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* realtime:
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* The current uptime is incremented with all outstanding ticks.
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* proc_ptr, bill_ptr:
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* These are used for accounting. It does not matter if proc.c
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* is changing them, provided they are always valid pointers,
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* since at worst the previous process would be billed.
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*/
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register unsigned ticks;
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/* Acknowledge the PS/2 clock interrupt. */
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if (machine.ps_mca) outb(PORT_B, inb(PORT_B) | CLOCK_ACK_BIT);
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/* Get number of ticks and update realtime. */
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ticks = lost_ticks + 1;
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lost_ticks = 0;
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realtime += ticks;
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/* Update user and system accounting times. Charge the current process for
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* user time. If the current process is not billable, that is, if a non-user
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* process is running, charge the billable process for system time as well.
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* Thus the unbillable process' user time is the billable user's system time.
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*/
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proc_ptr->p_user_time += ticks;
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if (priv(proc_ptr)->s_flags & PREEMPTIBLE) {
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proc_ptr->p_ticks_left -= ticks;
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}
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if (! (priv(proc_ptr)->s_flags & BILLABLE)) {
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bill_ptr->p_sys_time += ticks;
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bill_ptr->p_ticks_left -= ticks;
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}
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/* Update load average. */
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load_update();
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/* Check if do_clocktick() must be called. Done for alarms and scheduling.
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* Some processes, such as the kernel tasks, cannot be preempted.
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*/
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if ((next_timeout <= realtime) || (proc_ptr->p_ticks_left <= 0)) {
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prev_ptr = proc_ptr; /* store running process */
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lock_notify(HARDWARE, CLOCK); /* send notification */
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}
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return(1); /* reenable interrupts */
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}
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/*===========================================================================*
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* get_uptime *
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*===========================================================================*/
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PUBLIC clock_t get_uptime()
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{
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/* Get and return the current clock uptime in ticks. */
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return(realtime);
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}
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/*===========================================================================*
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* set_timer *
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*===========================================================================*/
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PUBLIC void set_timer(tp, exp_time, watchdog)
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struct timer *tp; /* pointer to timer structure */
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clock_t exp_time; /* expiration realtime */
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tmr_func_t watchdog; /* watchdog to be called */
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{
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/* Insert the new timer in the active timers list. Always update the
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* next timeout time by setting it to the front of the active list.
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*/
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tmrs_settimer(&clock_timers, tp, exp_time, watchdog, NULL);
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next_timeout = clock_timers->tmr_exp_time;
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}
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/*===========================================================================*
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* reset_timer *
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*===========================================================================*/
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PUBLIC void reset_timer(tp)
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struct timer *tp; /* pointer to timer structure */
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{
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/* The timer pointed to by 'tp' is no longer needed. Remove it from both the
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* active and expired lists. Always update the next timeout time by setting
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* it to the front of the active list.
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*/
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tmrs_clrtimer(&clock_timers, tp, NULL);
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next_timeout = (clock_timers == NULL) ?
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TMR_NEVER : clock_timers->tmr_exp_time;
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}
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/*===========================================================================*
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* read_clock *
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*===========================================================================*/
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PUBLIC unsigned long read_clock()
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{
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/* Read the counter of channel 0 of the 8253A timer. This counter counts
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* down at a rate of TIMER_FREQ and restarts at TIMER_COUNT-1 when it
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* reaches zero. A hardware interrupt (clock tick) occurs when the counter
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* gets to zero and restarts its cycle.
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*/
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unsigned count;
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outb(TIMER_MODE, LATCH_COUNT);
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count = inb(TIMER0);
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count |= (inb(TIMER0) << 8);
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return count;
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}
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/*===========================================================================*
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* load_update *
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*===========================================================================*/
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PRIVATE void load_update(void)
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{
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u16_t slot;
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/* Load average data is stored as a list of numbers in a circular
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* buffer. Each slot accumulates _LOAD_UNIT_SECS of samples of
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* the number of runnable processes. Computations can then
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* be made of the load average over variable periods, in the
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* user library (see getloadavg(3)).
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*/
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slot = (realtime / HZ / _LOAD_UNIT_SECS) % _LOAD_HISTORY;
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if(slot != kloadinfo.proc_last_slot) {
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kloadinfo.proc_load_history[slot] = 0;
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kloadinfo.proc_last_slot = slot;
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}
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/* Cumulation. */
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kloadinfo.proc_load_history[slot] += kloadinfo.procs_enqueued;
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/* Up-to-dateness. */
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kloadinfo.last_clock = realtime;
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}
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