2 * linux/arch/parisc/kernel/time.c
4 * Copyright (C) 1991, 1992, 1995 Linus Torvalds
5 * Modifications for ARM (C) 1994, 1995, 1996,1997 Russell King
6 * Copyright (C) 1999 SuSE GmbH, (Philipp Rumpf, prumpf@tux.org)
8 * 1994-07-02 Alan Modra
9 * fixed set_rtc_mmss, fixed time.year for >= 2000, new mktime
10 * 1998-12-20 Updated NTP code according to technical memorandum Jan '96
11 * "A Kernel Model for Precision Timekeeping" by Dave Mills
13 #include <linux/errno.h>
14 #include <linux/module.h>
15 #include <linux/sched.h>
16 #include <linux/kernel.h>
17 #include <linux/param.h>
18 #include <linux/string.h>
20 #include <linux/interrupt.h>
21 #include <linux/time.h>
22 #include <linux/init.h>
23 #include <linux/smp.h>
24 #include <linux/profile.h>
26 #include <asm/uaccess.h>
29 #include <asm/param.h>
33 #include <linux/timex.h>
35 static unsigned long clocktick __read_mostly; /* timer cycles per tick */
38 extern void smp_do_timer(struct pt_regs *regs);
42 * We keep time on PA-RISC Linux by using the Interval Timer which is
43 * a pair of registers; one is read-only and one is write-only; both
44 * accessed through CR16. The read-only register is 32 or 64 bits wide,
45 * and increments by 1 every CPU clock tick. The architecture only
46 * guarantees us a rate between 0.5 and 2, but all implementations use a
47 * rate of 1. The write-only register is 32-bits wide. When the lowest
48 * 32 bits of the read-only register compare equal to the write-only
49 * register, it raises a maskable external interrupt. Each processor has
50 * an Interval Timer of its own and they are not synchronised.
52 * We want to generate an interrupt every 1/HZ seconds. So we program
53 * CR16 to interrupt every @clocktick cycles. The it_value in cpu_data
54 * is programmed with the intended time of the next tick. We can be
55 * held off for an arbitrarily long period of time by interrupts being
56 * disabled, so we may miss one or more ticks.
58 irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
61 unsigned long next_tick;
62 unsigned long cycles_elapsed, ticks_elapsed;
63 unsigned long cycles_remainder;
64 unsigned int cpu = smp_processor_id();
66 /* gcc can optimize for "read-only" case with a local clocktick */
67 unsigned long cpt = clocktick;
69 profile_tick(CPU_PROFILING);
71 /* Initialize next_tick to the expected tick time. */
72 next_tick = cpu_data[cpu].it_value;
74 /* Get current interval timer.
75 * CR16 reads as 64 bits in CPU wide mode.
76 * CR16 reads as 32 bits in CPU narrow mode.
80 cycles_elapsed = now - next_tick;
82 if ((cycles_elapsed >> 5) < cpt) {
83 /* use "cheap" math (add/subtract) instead
84 * of the more expensive div/mul method
86 cycles_remainder = cycles_elapsed;
88 while (cycles_remainder > cpt) {
89 cycles_remainder -= cpt;
93 cycles_remainder = cycles_elapsed % cpt;
94 ticks_elapsed = 1 + cycles_elapsed / cpt;
97 /* Can we differentiate between "early CR16" (aka Scenario 1) and
98 * "long delay" (aka Scenario 3)? I don't think so.
100 * We expected timer_interrupt to be delivered at least a few hundred
101 * cycles after the IT fires. But it's arbitrary how much time passes
102 * before we call it "late". I've picked one second.
104 if (ticks_elapsed > HZ) {
105 /* Scenario 3: very long delay? bad in any case */
106 printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!"
107 " cycles %lX rem %lX "
108 " next/now %lX/%lX\n",
110 cycles_elapsed, cycles_remainder,
114 /* convert from "division remainder" to "remainder of clock tick" */
115 cycles_remainder = cpt - cycles_remainder;
117 /* Determine when (in CR16 cycles) next IT interrupt will fire.
118 * We want IT to fire modulo clocktick even if we miss/skip some.
119 * But those interrupts don't in fact get delivered that regularly.
121 next_tick = now + cycles_remainder;
123 cpu_data[cpu].it_value = next_tick;
125 /* Skip one clocktick on purpose if we are likely to miss next_tick.
126 * We want to avoid the new next_tick being less than CR16.
127 * If that happened, itimer wouldn't fire until CR16 wrapped.
128 * We'll catch the tick we missed on the tick after that.
130 if (!(cycles_remainder >> 13))
133 /* Program the IT when to deliver the next interrupt. */
134 /* Only bottom 32-bits of next_tick are written to cr16. */
135 mtctl(next_tick, 16);
138 /* Done mucking with unreliable delivery of interrupts.
139 * Go do system house keeping.
144 update_process_times(user_mode(regs));
147 write_seqlock(&xtime_lock);
148 do_timer(ticks_elapsed);
149 write_sequnlock(&xtime_lock);
152 /* check soft power switch status */
153 if (cpu == 0 && !atomic_read(&power_tasklet.count))
154 tasklet_schedule(&power_tasklet);
160 unsigned long profile_pc(struct pt_regs *regs)
162 unsigned long pc = instruction_pointer(regs);
164 if (regs->gr[0] & PSW_N)
168 if (in_lock_functions(pc))
174 EXPORT_SYMBOL(profile_pc);
178 * Return the number of micro-seconds that elapsed since the last
179 * update to wall time (aka xtime). The xtime_lock
180 * must be at least read-locked when calling this routine.
182 static inline unsigned long gettimeoffset (void)
186 * FIXME: This won't work on smp because jiffies are updated by cpu 0.
187 * Once parisc-linux learns the cr16 difference between processors,
188 * this could be made to work.
191 unsigned long prev_tick;
192 unsigned long next_tick;
193 unsigned long elapsed_cycles;
195 unsigned long cpuid = smp_processor_id();
196 unsigned long cpt = clocktick;
198 next_tick = cpu_data[cpuid].it_value;
199 now = mfctl(16); /* Read the hardware interval timer. */
201 prev_tick = next_tick - cpt;
203 /* Assume Scenario 1: "now" is later than prev_tick. */
204 elapsed_cycles = now - prev_tick;
206 /* aproximate HZ with shifts. Intended math is "(elapsed/clocktick) > HZ" */
208 if (elapsed_cycles > (cpt << 10) )
210 if (elapsed_cycles > (cpt << 8) )
212 if (elapsed_cycles > (cpt << 7) )
214 #warn WTF is HZ set to anyway?
215 if (elapsed_cycles > (HZ * cpt) )
218 /* Scenario 3: clock ticks are missing. */
219 printk (KERN_CRIT "gettimeoffset(CPU %ld): missing %ld ticks!"
220 " cycles %lX prev/now/next %lX/%lX/%lX clock %lX\n",
221 cpuid, elapsed_cycles / cpt,
222 elapsed_cycles, prev_tick, now, next_tick, cpt);
225 /* FIXME: Can we improve the precision? Not with PAGE0. */
226 usec = (elapsed_cycles * 10000) / PAGE0->mem_10msec;
234 do_gettimeofday (struct timeval *tv)
236 unsigned long flags, seq, usec, sec;
238 /* Hold xtime_lock and adjust timeval. */
240 seq = read_seqbegin_irqsave(&xtime_lock, flags);
241 usec = gettimeoffset();
243 usec += (xtime.tv_nsec / 1000);
244 } while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
246 /* Move adjusted usec's into sec's. */
247 while (usec >= USEC_PER_SEC) {
248 usec -= USEC_PER_SEC;
252 /* Return adjusted result. */
257 EXPORT_SYMBOL(do_gettimeofday);
260 do_settimeofday (struct timespec *tv)
262 time_t wtm_sec, sec = tv->tv_sec;
263 long wtm_nsec, nsec = tv->tv_nsec;
265 if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
268 write_seqlock_irq(&xtime_lock);
271 * This is revolting. We need to set "xtime"
272 * correctly. However, the value in this location is
273 * the value at the most recent update of wall time.
274 * Discover what correction gettimeofday would have
275 * done, and then undo it!
277 nsec -= gettimeoffset() * 1000;
279 wtm_sec = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
280 wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
282 set_normalized_timespec(&xtime, sec, nsec);
283 set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
287 write_sequnlock_irq(&xtime_lock);
291 EXPORT_SYMBOL(do_settimeofday);
294 * XXX: We can do better than this.
295 * Returns nanoseconds
298 unsigned long long sched_clock(void)
300 return (unsigned long long)jiffies * (1000000000 / HZ);
304 void __init start_cpu_itimer(void)
306 unsigned int cpu = smp_processor_id();
307 unsigned long next_tick = mfctl(16) + clocktick;
309 mtctl(next_tick, 16); /* kick off Interval Timer (CR16) */
311 cpu_data[cpu].it_value = next_tick;
314 void __init time_init(void)
316 static struct pdc_tod tod_data;
318 clocktick = (100 * PAGE0->mem_10msec) / HZ;
320 start_cpu_itimer(); /* get CPU 0 started */
322 if (pdc_tod_read(&tod_data) == 0) {
325 write_seqlock_irqsave(&xtime_lock, flags);
326 xtime.tv_sec = tod_data.tod_sec;
327 xtime.tv_nsec = tod_data.tod_usec * 1000;
328 set_normalized_timespec(&wall_to_monotonic,
329 -xtime.tv_sec, -xtime.tv_nsec);
330 write_sequnlock_irqrestore(&xtime_lock, flags);
332 printk(KERN_ERR "Error reading tod clock\n");