/* This file contains the code and data for the clock task. The clock task * has a single entry point, clock_task(). It accepts four message types: * * HARD_INT: a clock interrupt has occurred * GET_TIME: a process wants the real time * SET_TIME: a process wants to set the real time * SET_ALARM: a process wants to be alerted after a specified interval * * The input message is format m6. The parameters are as follows: * * m_type CLOCK_PROC FUNC NEW_TIME * --------------------------------------------- * | SET_ALARM | proc_nr |f to call| delta | * |------------+----------+---------+---------| * | HARD_INT | | | | * |------------+----------+---------+---------| * | GET_TIME | | | | * |------------+----------+---------+---------| * | SET_TIME | | | newtime | * --------------------------------------------- * * When an alarm goes off, if the caller is a user process, a SIGALRM signal * is sent to it. If it is a task, a function specified by the caller will * be invoked. This function may, for example, send a message, but only if * it is certain that the task will be blocked when the timer goes off. */ #include "kernel.h" #include <signal.h> #include <minix/callnr.h> #include <minix/com.h> #include "proc.h" /* Constant definitions. */ #define MILLISEC 100 /* how often to call the scheduler (msec) */ #define SCHED_RATE (MILLISEC*HZ/1000) /* number of ticks per schedule */ /* Clock parameters. */ #if (CHIP == INTEL) #define COUNTER_FREQ (2*TIMER_FREQ) /* counter frequency using sqare 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 */ #endif #if (CHIP == M68000) #define FLUSH_MASK 0x07 /* bit mask used for flushing RS232 input */ #define TIMER_FREQ 2457600L /* timer 3 input clock frequency */ #endif /* Clock task variables. */ PRIVATE time_t boot_time; /* time in seconds of system boot */ PRIVATE time_t next_alarm; /* probable time of next alarm */ PRIVATE time_t pending_ticks; /* ticks seen by low level only */ PRIVATE time_t realtime; /* real time clock */ PRIVATE int sched_ticks = SCHED_RATE; /* counter: when 0, call scheduler */ PRIVATE struct proc *prev_ptr; /* last user process run by clock task */ PRIVATE message mc; /* message buffer for both input and output */ PRIVATE void (*watch_dog[NR_TASKS+1])(); /* watch_dog functions to call */ FORWARD void do_clocktick(); FORWARD void do_get_time(); FORWARD void do_set_time(); FORWARD void do_setalarm(); FORWARD void init_clock(); /*===========================================================================* * clock_task * *===========================================================================*/ PUBLIC void clock_task() { /* Main program of clock task. It determines which of the 4 possible * calls this is by looking at 'mc.m_type'. Then it dispatches. */ int opcode; init_clock(); /* initialize clock task */ /* Main loop of the clock task. Get work, process it, sometimes reply. */ while (TRUE) { receive(ANY, &mc); /* go get a message */ opcode = mc.m_type; /* extract the function code */ lock(); realtime += pending_ticks; /* transfer ticks from low level handler */ pending_ticks = 0; unlock(); switch (opcode) { case SET_ALARM: do_setalarm(&mc); break; case GET_TIME: do_get_time(); break; case SET_TIME: do_set_time(&mc); break; case HARD_INT: do_clocktick(); break; default: panic("clock task got bad message", mc.m_type); } /* Send reply, except for clock tick. */ mc.m_type = OK; if (opcode != HARD_INT) send(mc.m_source, &mc); } } /*===========================================================================* * do_setalarm * *===========================================================================*/ PRIVATE void do_setalarm(m_ptr) message *m_ptr; /* pointer to request message */ { /* A process wants an alarm signal or a task wants a given watch_dog function * called after a specified interval. Record the request and check to see * it is the very next alarm needed. */ register struct proc *rp; int proc_nr; /* which process wants the alarm */ long delta_ticks; /* in how many clock ticks does he want it? */ void (*function)(); /* function to call (tasks only) */ /* Extract the parameters from the message. */ proc_nr = m_ptr->CLOCK_PROC_NR; /* process to interrupt later */ delta_ticks = m_ptr->DELTA_TICKS; /* how many ticks to wait */ function = m_ptr->FUNC_TO_CALL; /* function to call (tasks only) */ rp = proc_addr(proc_nr); mc.SECONDS_LEFT = (rp->p_alarm == 0L ? 0 : (rp->p_alarm - realtime)/HZ ); rp->p_alarm = (delta_ticks == 0L ? 0L : realtime + delta_ticks); if (istaskp(rp)) watch_dog[-proc_nr] = function; /* Which alarm is next? */ next_alarm = MAX_P_LONG; for (rp = BEG_PROC_ADDR; rp < END_PROC_ADDR; rp++) if(rp->p_alarm != 0 && rp->p_alarm < next_alarm)next_alarm=rp->p_alarm; } /*===========================================================================* * do_get_time * *===========================================================================*/ PRIVATE void do_get_time() { /* Get and return the current clock time in ticks. */ mc.m_type = REAL_TIME; /* set message type for reply */ mc.NEW_TIME = boot_time + realtime/HZ; /* current real time */ } /*===========================================================================* * do_set_time * *===========================================================================*/ PRIVATE void do_set_time(m_ptr) message *m_ptr; /* pointer to request message */ { /* Set the real time clock. Only the superuser can use this call. */ boot_time = m_ptr->NEW_TIME - realtime/HZ; } /*===========================================================================* * do_clocktick * *===========================================================================*/ PRIVATE void do_clocktick() { /* This routine called on clock ticks when a lot of work needs to be done. */ register struct proc *rp; register int proc_nr; if (next_alarm <= realtime) { /* An alarm may have gone off, but proc may have exited, so check. */ next_alarm = MAX_P_LONG; /* start computing next alarm */ for (rp = BEG_PROC_ADDR; rp < END_PROC_ADDR; rp++) { if (rp->p_alarm != (time_t) 0) { /* See if this alarm time has been reached. */ if (rp->p_alarm <= realtime) { /* A timer has gone off. If it is a user proc, * send it a signal. If it is a task, call the * function previously specified by the task. */ if ( (proc_nr = proc_number(rp)) >= 0) cause_sig(proc_nr, SIGALRM); else (*watch_dog[-proc_nr])(); rp->p_alarm = 0; } /* Work on determining which alarm is next. */ if (rp->p_alarm != 0 && rp->p_alarm < next_alarm) next_alarm = rp->p_alarm; } } } /* 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 */ } #if (CHIP == M68000) if (rdy_head[SHADOW_Q]) unshadow(rdy_head[SHADOW_Q]); #endif } #if (CHIP == INTEL) /*===========================================================================* * init_clock * *===========================================================================*/ PRIVATE void init_clock() { /* Initialize channel 0 of the 8253A timer to e.g. 60 Hz. */ out_byte(TIMER_MODE, SQUARE_WAVE); /* set timer to run continuously */ out_byte(TIMER0, TIMER_COUNT); /* load timer low byte */ out_byte(TIMER0, TIMER_COUNT >> 8); /* load timer high byte */ enable_irq(CLOCK_IRQ); /* ready for clock interrupts */ } /*==========================================================================* * milli_delay * *==========================================================================*/ PUBLIC void milli_delay(millisec) unsigned millisec; { /* Delay some milliseconds (or longer - interrupts may interfere). */ register unsigned count; register unsigned diff; unsigned prev_count; unsigned long total_count; total_count = (unsigned long) millisec * (COUNTER_FREQ / 1000); diff = 100; /* guess for emergencies */ prev_count = read_counter(); while (TRUE) { count = read_counter(); /* Use difference between counts unless counter has not changed * (broken?) or has increased (due to reset). */ if (count < prev_count) diff = prev_count - count; if (diff >= total_count) break; total_count -= diff; prev_count = count; } } /*==========================================================================* * read_counter * *==========================================================================*/ PUBLIC unsigned read_counter() { /* Read the counter for channel 0 of the 8253A timer. The counter decrements * at twice the timer frequency (one full cycle for each half of square wave). * The counter normally has a value between 0 and TIMER_COUNT, but before * the clock task has been initialized, its maximum value is 65535, as set by * the BIOS. */ register unsigned low_byte; out_byte(TIMER_MODE, LATCH_COUNT); /* make chip copy count to latch */ low_byte = in_byte(TIMER0); /* countdown continues during 2-step read */ return((in_byte(TIMER0) << 8) + low_byte); } #endif #if (CHIP == M68000) #include "staddr.h" #include "stmfp.h" /*===========================================================================* * init_clock * *===========================================================================*/ PRIVATE void init_clock() { /* Initialize the timer C in the MFP 68901. * Reducing to HZ is not possible by hardware. The resulting interrupt * rate is further reduced by software with a factor of 4. * Note that the expression below works for both HZ=50 and HZ=60. */ do MFP->mf_tcdr = TIMER_FREQ/(64*4*HZ); while ((MFP->mf_tcdr & 0xFF) != TIMER_FREQ/(64*4*HZ)); MFP->mf_tcdcr |= (T_Q064<<4); } #endif /*===========================================================================* * clock_handler * *===========================================================================*/ PUBLIC void clock_handler() { /* 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. * Also call TTY and PRINTER and let them do whatever is necessary. * * 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_alarm, realtime, sched_ticks, bill_ptr, prev_ptr, * rdy_head[USER_Q]: * These are tested to decide whether to call interrupt(). 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 an explicit lock in clock.c. Don't * update realtime directly, since there are too many * references to it to guard conveniently. * 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; /* Update user and system accounting times. * First charge the current process for user time. * If the current process is not the billable process (usually because it * is a task), charge the billable process for system time as well. * Thus the unbillable tasks' user time is the billable users' system time. */ if (k_reenter != 0) rp = cproc_addr(HARDWARE); else rp = proc_ptr; ++rp->user_time; if (rp != bill_ptr) ++bill_ptr->sys_time; ++pending_ticks; #if (CHIP != M68000) tty_wakeup(); /* possibly wake up TTY */ pr_restart(); /* possibly restart printer */ #endif #if (CHIP == M68000) kb_timer(); /* keyboard repeat */ if (sched_ticks == 1) fd_timer(); /* floppy deselect */ /* If input characters are accumulating on an RS232 line, process them. */ if (flush_flag) { if ( (((int)(realtime+pending_ticks)) & FLUSH_MASK) == 0) rs_flush(); /* only low-order bits of realtime mattered */ } #endif if (next_alarm <= realtime + pending_ticks || sched_ticks == 1 && bill_ptr == prev_ptr && #if (CHIP != M68000) rdy_head[USER_Q] != NIL_PROC) { #else (rdy_head[USER_Q] != NIL_PROC || rdy_head[SHADOW_Q] != NIL_PROC)) { #endif interrupt(CLOCK); return; } if (--sched_ticks == 0) { /* If bill_ptr == prev_ptr, no ready users so don't need sched(). */ sched_ticks = SCHED_RATE; /* reset quantum */ prev_ptr = bill_ptr; /* new previous process */ } }