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 * We keep time on PA-RISC Linux by using the Interval Timer which is
39 * a pair of registers; one is read-only and one is write-only; both
40 * accessed through CR16. The read-only register is 32 or 64 bits wide,
41 * and increments by 1 every CPU clock tick. The architecture only
42 * guarantees us a rate between 0.5 and 2, but all implementations use a
43 * rate of 1. The write-only register is 32-bits wide. When the lowest
44 * 32 bits of the read-only register compare equal to the write-only
45 * register, it raises a maskable external interrupt. Each processor has
46 * an Interval Timer of its own and they are not synchronised.
48 * We want to generate an interrupt every 1/HZ seconds. So we program
49 * CR16 to interrupt every @clocktick cycles. The it_value in cpu_data
50 * is programmed with the intended time of the next tick. We can be
51 * held off for an arbitrarily long period of time by interrupts being
52 * disabled, so we may miss one or more ticks.
54 irqreturn_t
timer_interrupt(int irq
, void *dev_id
)
57 unsigned long next_tick
;
58 unsigned long cycles_elapsed
, ticks_elapsed
;
59 unsigned long cycles_remainder
;
60 unsigned int cpu
= smp_processor_id();
61 struct cpuinfo_parisc
*cpuinfo
= &cpu_data
[cpu
];
63 /* gcc can optimize for "read-only" case with a local clocktick */
64 unsigned long cpt
= clocktick
;
66 profile_tick(CPU_PROFILING
);
68 /* Initialize next_tick to the expected tick time. */
69 next_tick
= cpuinfo
->it_value
;
71 /* Get current interval timer.
72 * CR16 reads as 64 bits in CPU wide mode.
73 * CR16 reads as 32 bits in CPU narrow mode.
77 cycles_elapsed
= now
- next_tick
;
79 if ((cycles_elapsed
>> 5) < cpt
) {
80 /* use "cheap" math (add/subtract) instead
81 * of the more expensive div/mul method
83 cycles_remainder
= cycles_elapsed
;
85 while (cycles_remainder
> cpt
) {
86 cycles_remainder
-= cpt
;
90 cycles_remainder
= cycles_elapsed
% cpt
;
91 ticks_elapsed
= 1 + cycles_elapsed
/ cpt
;
94 /* Can we differentiate between "early CR16" (aka Scenario 1) and
95 * "long delay" (aka Scenario 3)? I don't think so.
97 * We expected timer_interrupt to be delivered at least a few hundred
98 * cycles after the IT fires. But it's arbitrary how much time passes
99 * before we call it "late". I've picked one second.
101 if (ticks_elapsed
> HZ
) {
102 /* Scenario 3: very long delay? bad in any case */
103 printk (KERN_CRIT
"timer_interrupt(CPU %d): delayed!"
104 " cycles %lX rem %lX "
105 " next/now %lX/%lX\n",
107 cycles_elapsed
, cycles_remainder
,
111 /* convert from "division remainder" to "remainder of clock tick" */
112 cycles_remainder
= cpt
- cycles_remainder
;
114 /* Determine when (in CR16 cycles) next IT interrupt will fire.
115 * We want IT to fire modulo clocktick even if we miss/skip some.
116 * But those interrupts don't in fact get delivered that regularly.
118 next_tick
= now
+ cycles_remainder
;
120 cpuinfo
->it_value
= next_tick
;
122 /* Skip one clocktick on purpose if we are likely to miss next_tick.
123 * We want to avoid the new next_tick being less than CR16.
124 * If that happened, itimer wouldn't fire until CR16 wrapped.
125 * We'll catch the tick we missed on the tick after that.
127 if (!(cycles_remainder
>> 13))
130 /* Program the IT when to deliver the next interrupt. */
131 /* Only bottom 32-bits of next_tick are written to cr16. */
132 mtctl(next_tick
, 16);
135 /* Done mucking with unreliable delivery of interrupts.
136 * Go do system house keeping.
139 if (!--cpuinfo
->prof_counter
) {
140 cpuinfo
->prof_counter
= cpuinfo
->prof_multiplier
;
141 update_process_times(user_mode(get_irq_regs()));
145 write_seqlock(&xtime_lock
);
146 do_timer(ticks_elapsed
);
147 write_sequnlock(&xtime_lock
);
150 /* check soft power switch status */
151 if (cpu
== 0 && !atomic_read(&power_tasklet
.count
))
152 tasklet_schedule(&power_tasklet
);
158 unsigned long profile_pc(struct pt_regs
*regs
)
160 unsigned long pc
= instruction_pointer(regs
);
162 if (regs
->gr
[0] & PSW_N
)
166 if (in_lock_functions(pc
))
172 EXPORT_SYMBOL(profile_pc
);
176 * Return the number of micro-seconds that elapsed since the last
177 * update to wall time (aka xtime). The xtime_lock
178 * must be at least read-locked when calling this routine.
180 static inline unsigned long gettimeoffset (void)
184 * FIXME: This won't work on smp because jiffies are updated by cpu 0.
185 * Once parisc-linux learns the cr16 difference between processors,
186 * this could be made to work.
189 unsigned long prev_tick
;
190 unsigned long next_tick
;
191 unsigned long elapsed_cycles
;
193 unsigned long cpuid
= smp_processor_id();
194 unsigned long cpt
= clocktick
;
196 next_tick
= cpu_data
[cpuid
].it_value
;
197 now
= mfctl(16); /* Read the hardware interval timer. */
199 prev_tick
= next_tick
- cpt
;
201 /* Assume Scenario 1: "now" is later than prev_tick. */
202 elapsed_cycles
= now
- prev_tick
;
204 /* aproximate HZ with shifts. Intended math is "(elapsed/clocktick) > HZ" */
206 if (elapsed_cycles
> (cpt
<< 10) )
208 if (elapsed_cycles
> (cpt
<< 8) )
210 if (elapsed_cycles
> (cpt
<< 7) )
212 #warn WTF is HZ set to anyway?
213 if (elapsed_cycles
> (HZ
* cpt
) )
216 /* Scenario 3: clock ticks are missing. */
217 printk (KERN_CRIT
"gettimeoffset(CPU %ld): missing %ld ticks!"
218 " cycles %lX prev/now/next %lX/%lX/%lX clock %lX\n",
219 cpuid
, elapsed_cycles
/ cpt
,
220 elapsed_cycles
, prev_tick
, now
, next_tick
, cpt
);
223 /* FIXME: Can we improve the precision? Not with PAGE0. */
224 usec
= (elapsed_cycles
* 10000) / PAGE0
->mem_10msec
;
232 do_gettimeofday (struct timeval
*tv
)
234 unsigned long flags
, seq
, usec
, sec
;
236 /* Hold xtime_lock and adjust timeval. */
238 seq
= read_seqbegin_irqsave(&xtime_lock
, flags
);
239 usec
= gettimeoffset();
241 usec
+= (xtime
.tv_nsec
/ 1000);
242 } while (read_seqretry_irqrestore(&xtime_lock
, seq
, flags
));
244 /* Move adjusted usec's into sec's. */
245 while (usec
>= USEC_PER_SEC
) {
246 usec
-= USEC_PER_SEC
;
250 /* Return adjusted result. */
255 EXPORT_SYMBOL(do_gettimeofday
);
258 do_settimeofday (struct timespec
*tv
)
260 time_t wtm_sec
, sec
= tv
->tv_sec
;
261 long wtm_nsec
, nsec
= tv
->tv_nsec
;
263 if ((unsigned long)tv
->tv_nsec
>= NSEC_PER_SEC
)
266 write_seqlock_irq(&xtime_lock
);
269 * This is revolting. We need to set "xtime"
270 * correctly. However, the value in this location is
271 * the value at the most recent update of wall time.
272 * Discover what correction gettimeofday would have
273 * done, and then undo it!
275 nsec
-= gettimeoffset() * 1000;
277 wtm_sec
= wall_to_monotonic
.tv_sec
+ (xtime
.tv_sec
- sec
);
278 wtm_nsec
= wall_to_monotonic
.tv_nsec
+ (xtime
.tv_nsec
- nsec
);
280 set_normalized_timespec(&xtime
, sec
, nsec
);
281 set_normalized_timespec(&wall_to_monotonic
, wtm_sec
, wtm_nsec
);
285 write_sequnlock_irq(&xtime_lock
);
289 EXPORT_SYMBOL(do_settimeofday
);
291 void __init
start_cpu_itimer(void)
293 unsigned int cpu
= smp_processor_id();
294 unsigned long next_tick
= mfctl(16) + clocktick
;
296 mtctl(next_tick
, 16); /* kick off Interval Timer (CR16) */
298 cpu_data
[cpu
].it_value
= next_tick
;
301 void __init
time_init(void)
303 static struct pdc_tod tod_data
;
305 clocktick
= (100 * PAGE0
->mem_10msec
) / HZ
;
307 start_cpu_itimer(); /* get CPU 0 started */
309 if (pdc_tod_read(&tod_data
) == 0) {
312 write_seqlock_irqsave(&xtime_lock
, flags
);
313 xtime
.tv_sec
= tod_data
.tod_sec
;
314 xtime
.tv_nsec
= tod_data
.tod_usec
* 1000;
315 set_normalized_timespec(&wall_to_monotonic
,
316 -xtime
.tv_sec
, -xtime
.tv_nsec
);
317 write_sequnlock_irqrestore(&xtime_lock
, flags
);
319 printk(KERN_ERR
"Error reading tod clock\n");
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