2 * linux/kernel/time/ntp.c
4 * NTP state machine interfaces and logic.
6 * This code was mainly moved from kernel/timer.c and kernel/time.c
7 * Please see those files for relevant copyright info and historical
12 #include <linux/time.h>
13 #include <linux/timex.h>
15 #include <asm/div64.h>
16 #include <asm/timex.h>
19 * Timekeeping variables
21 unsigned long tick_usec
= TICK_USEC
; /* USER_HZ period (usec) */
22 unsigned long tick_nsec
; /* ACTHZ period (nsec) */
23 static u64 tick_length
, tick_length_base
;
25 #define MAX_TICKADJ 500 /* microsecs */
26 #define MAX_TICKADJ_SCALED (((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
27 TICK_LENGTH_SHIFT) / NTP_INTERVAL_FREQ)
30 * phase-lock loop variables
32 /* TIME_ERROR prevents overwriting the CMOS clock */
33 static int time_state
= TIME_OK
; /* clock synchronization status */
34 int time_status
= STA_UNSYNC
; /* clock status bits */
35 static long time_offset
; /* time adjustment (ns) */
36 static long time_constant
= 2; /* pll time constant */
37 long time_maxerror
= NTP_PHASE_LIMIT
; /* maximum error (us) */
38 long time_esterror
= NTP_PHASE_LIMIT
; /* estimated error (us) */
39 long time_freq
; /* frequency offset (scaled ppm)*/
40 static long time_reftime
; /* time at last adjustment (s) */
43 #define CLOCK_TICK_OVERFLOW (LATCH * HZ - CLOCK_TICK_RATE)
44 #define CLOCK_TICK_ADJUST (((s64)CLOCK_TICK_OVERFLOW * NSEC_PER_SEC) / \
47 static void ntp_update_frequency(void)
49 u64 second_length
= (u64
)(tick_usec
* NSEC_PER_USEC
* USER_HZ
)
51 second_length
+= (s64
)CLOCK_TICK_ADJUST
<< TICK_LENGTH_SHIFT
;
52 second_length
+= (s64
)time_freq
<< (TICK_LENGTH_SHIFT
- SHIFT_NSEC
);
54 tick_length_base
= second_length
;
56 do_div(second_length
, HZ
);
57 tick_nsec
= second_length
>> TICK_LENGTH_SHIFT
;
59 do_div(tick_length_base
, NTP_INTERVAL_FREQ
);
63 * ntp_clear - Clears the NTP state variables
65 * Must be called while holding a write on the xtime_lock
69 time_adjust
= 0; /* stop active adjtime() */
70 time_status
|= STA_UNSYNC
;
71 time_maxerror
= NTP_PHASE_LIMIT
;
72 time_esterror
= NTP_PHASE_LIMIT
;
74 ntp_update_frequency();
76 tick_length
= tick_length_base
;
81 * this routine handles the overflow of the microsecond field
83 * The tricky bits of code to handle the accurate clock support
84 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
85 * They were originally developed for SUN and DEC kernels.
86 * All the kudos should go to Dave for this stuff.
88 void second_overflow(void)
92 /* Bump the maxerror field */
93 time_maxerror
+= MAXFREQ
>> SHIFT_USEC
;
94 if (time_maxerror
> NTP_PHASE_LIMIT
) {
95 time_maxerror
= NTP_PHASE_LIMIT
;
96 time_status
|= STA_UNSYNC
;
100 * Leap second processing. If in leap-insert state at the end of the
101 * day, the system clock is set back one second; if in leap-delete
102 * state, the system clock is set ahead one second. The microtime()
103 * routine or external clock driver will insure that reported time is
104 * always monotonic. The ugly divides should be replaced.
106 switch (time_state
) {
108 if (time_status
& STA_INS
)
109 time_state
= TIME_INS
;
110 else if (time_status
& STA_DEL
)
111 time_state
= TIME_DEL
;
114 if (xtime
.tv_sec
% 86400 == 0) {
116 wall_to_monotonic
.tv_sec
++;
118 * The timer interpolator will make time change
119 * gradually instead of an immediate jump by one second
121 time_interpolator_update(-NSEC_PER_SEC
);
122 time_state
= TIME_OOP
;
124 printk(KERN_NOTICE
"Clock: inserting leap second "
129 if ((xtime
.tv_sec
+ 1) % 86400 == 0) {
131 wall_to_monotonic
.tv_sec
--;
133 * Use of time interpolator for a gradual change of
136 time_interpolator_update(NSEC_PER_SEC
);
137 time_state
= TIME_WAIT
;
139 printk(KERN_NOTICE
"Clock: deleting leap second "
144 time_state
= TIME_WAIT
;
147 if (!(time_status
& (STA_INS
| STA_DEL
)))
148 time_state
= TIME_OK
;
152 * Compute the phase adjustment for the next second. The offset is
153 * reduced by a fixed factor times the time constant.
155 tick_length
= tick_length_base
;
156 time_adj
= shift_right(time_offset
, SHIFT_PLL
+ time_constant
);
157 time_offset
-= time_adj
;
158 tick_length
+= (s64
)time_adj
<< (TICK_LENGTH_SHIFT
- SHIFT_UPDATE
);
160 if (unlikely(time_adjust
)) {
161 if (time_adjust
> MAX_TICKADJ
) {
162 time_adjust
-= MAX_TICKADJ
;
163 tick_length
+= MAX_TICKADJ_SCALED
;
164 } else if (time_adjust
< -MAX_TICKADJ
) {
165 time_adjust
+= MAX_TICKADJ
;
166 tick_length
-= MAX_TICKADJ_SCALED
;
168 tick_length
+= (s64
)(time_adjust
* NSEC_PER_USEC
/
169 NTP_INTERVAL_FREQ
) << TICK_LENGTH_SHIFT
;
176 * Return how long ticks are at the moment, that is, how much time
177 * update_wall_time_one_tick will add to xtime next time we call it
178 * (assuming no calls to do_adjtimex in the meantime).
179 * The return value is in fixed-point nanoseconds shifted by the
180 * specified number of bits to the right of the binary point.
181 * This function has no side-effects.
183 u64
current_tick_length(void)
189 void __attribute__ ((weak
)) notify_arch_cmos_timer(void)
194 /* adjtimex mainly allows reading (and writing, if superuser) of
195 * kernel time-keeping variables. used by xntpd.
197 int do_adjtimex(struct timex
*txc
)
199 long ltemp
, mtemp
, save_adjust
;
200 s64 freq_adj
, temp64
;
203 /* In order to modify anything, you gotta be super-user! */
204 if (txc
->modes
&& !capable(CAP_SYS_TIME
))
207 /* Now we validate the data before disabling interrupts */
209 if ((txc
->modes
& ADJ_OFFSET_SINGLESHOT
) == ADJ_OFFSET_SINGLESHOT
)
210 /* singleshot must not be used with any other mode bits */
211 if (txc
->modes
!= ADJ_OFFSET_SINGLESHOT
)
214 if (txc
->modes
!= ADJ_OFFSET_SINGLESHOT
&& (txc
->modes
& ADJ_OFFSET
))
215 /* adjustment Offset limited to +- .512 seconds */
216 if (txc
->offset
<= - MAXPHASE
|| txc
->offset
>= MAXPHASE
)
219 /* if the quartz is off by more than 10% something is VERY wrong ! */
220 if (txc
->modes
& ADJ_TICK
)
221 if (txc
->tick
< 900000/USER_HZ
||
222 txc
->tick
> 1100000/USER_HZ
)
225 write_seqlock_irq(&xtime_lock
);
226 result
= time_state
; /* mostly `TIME_OK' */
228 /* Save for later - semantics of adjtime is to return old value */
229 save_adjust
= time_adjust
;
231 #if 0 /* STA_CLOCKERR is never set yet */
232 time_status
&= ~STA_CLOCKERR
; /* reset STA_CLOCKERR */
234 /* If there are input parameters, then process them */
237 if (txc
->modes
& ADJ_STATUS
) /* only set allowed bits */
238 time_status
= (txc
->status
& ~STA_RONLY
) |
239 (time_status
& STA_RONLY
);
241 if (txc
->modes
& ADJ_FREQUENCY
) { /* p. 22 */
242 if (txc
->freq
> MAXFREQ
|| txc
->freq
< -MAXFREQ
) {
246 time_freq
= ((s64
)txc
->freq
* NSEC_PER_USEC
)
247 >> (SHIFT_USEC
- SHIFT_NSEC
);
250 if (txc
->modes
& ADJ_MAXERROR
) {
251 if (txc
->maxerror
< 0 || txc
->maxerror
>= NTP_PHASE_LIMIT
) {
255 time_maxerror
= txc
->maxerror
;
258 if (txc
->modes
& ADJ_ESTERROR
) {
259 if (txc
->esterror
< 0 || txc
->esterror
>= NTP_PHASE_LIMIT
) {
263 time_esterror
= txc
->esterror
;
266 if (txc
->modes
& ADJ_TIMECONST
) { /* p. 24 */
267 if (txc
->constant
< 0) { /* NTP v4 uses values > 6 */
271 time_constant
= min(txc
->constant
+ 4, (long)MAXTC
);
274 if (txc
->modes
& ADJ_OFFSET
) { /* values checked earlier */
275 if (txc
->modes
== ADJ_OFFSET_SINGLESHOT
) {
276 /* adjtime() is independent from ntp_adjtime() */
277 time_adjust
= txc
->offset
;
279 else if (time_status
& STA_PLL
) {
280 ltemp
= txc
->offset
* NSEC_PER_USEC
;
283 * Scale the phase adjustment and
284 * clamp to the operating range.
286 time_offset
= min(ltemp
, MAXPHASE
* NSEC_PER_USEC
);
287 time_offset
= max(time_offset
, -MAXPHASE
* NSEC_PER_USEC
);
290 * Select whether the frequency is to be controlled
291 * and in which mode (PLL or FLL). Clamp to the operating
292 * range. Ugly multiply/divide should be replaced someday.
295 if (time_status
& STA_FREQHOLD
|| time_reftime
== 0)
296 time_reftime
= xtime
.tv_sec
;
297 mtemp
= xtime
.tv_sec
- time_reftime
;
298 time_reftime
= xtime
.tv_sec
;
300 freq_adj
= (s64
)time_offset
* mtemp
;
301 freq_adj
= shift_right(freq_adj
, time_constant
* 2 +
302 (SHIFT_PLL
+ 2) * 2 - SHIFT_NSEC
);
303 if (mtemp
>= MINSEC
&& (time_status
& STA_FLL
|| mtemp
> MAXSEC
)) {
304 temp64
= (s64
)time_offset
<< (SHIFT_NSEC
- SHIFT_FLL
);
305 if (time_offset
< 0) {
307 do_div(temp64
, mtemp
);
310 do_div(temp64
, mtemp
);
314 freq_adj
+= time_freq
;
315 freq_adj
= min(freq_adj
, (s64
)MAXFREQ_NSEC
);
316 time_freq
= max(freq_adj
, (s64
)-MAXFREQ_NSEC
);
317 time_offset
= (time_offset
/ NTP_INTERVAL_FREQ
)
320 } /* txc->modes & ADJ_OFFSET */
321 if (txc
->modes
& ADJ_TICK
)
322 tick_usec
= txc
->tick
;
324 if (txc
->modes
& (ADJ_TICK
|ADJ_FREQUENCY
|ADJ_OFFSET
))
325 ntp_update_frequency();
327 leave
: if ((time_status
& (STA_UNSYNC
|STA_CLOCKERR
)) != 0)
330 if ((txc
->modes
& ADJ_OFFSET_SINGLESHOT
) == ADJ_OFFSET_SINGLESHOT
)
331 txc
->offset
= save_adjust
;
333 txc
->offset
= shift_right(time_offset
, SHIFT_UPDATE
)
334 * NTP_INTERVAL_FREQ
/ 1000;
335 txc
->freq
= (time_freq
/ NSEC_PER_USEC
)
336 << (SHIFT_USEC
- SHIFT_NSEC
);
337 txc
->maxerror
= time_maxerror
;
338 txc
->esterror
= time_esterror
;
339 txc
->status
= time_status
;
340 txc
->constant
= time_constant
;
342 txc
->tolerance
= MAXFREQ
;
343 txc
->tick
= tick_usec
;
345 /* PPS is not implemented, so these are zero */
354 write_sequnlock_irq(&xtime_lock
);
355 do_gettimeofday(&txc
->time
);
356 notify_arch_cmos_timer();