projects/linux·blob v2.6.21 · refs

360 lines · 10.3 KiB

1/*
2 * linux/kernel/time/ntp.c
3 *
4 * NTP state machine interfaces and logic.
5 *
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
8 * changelogs.
9 */
10
11#include <linux/mm.h>
12#include <linux/time.h>
13#include <linux/timex.h>
14
15#include <asm/div64.h>
16#include <asm/timex.h>
17
18/*
19 * Timekeeping variables
20 */
21unsigned long tick_usec = TICK_USEC; /* USER_HZ period (usec) */
22unsigned long tick_nsec; /* ACTHZ period (nsec) */
23static u64 tick_length, tick_length_base;
24
25#define MAX_TICKADJ 500 /* microsecs */
26#define MAX_TICKADJ_SCALED (((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
27 TICK_LENGTH_SHIFT) / NTP_INTERVAL_FREQ)
28
29/*
30 * phase-lock loop variables
31 */
32/* TIME_ERROR prevents overwriting the CMOS clock */
33static int time_state = TIME_OK; /* clock synchronization status */
34int time_status = STA_UNSYNC; /* clock status bits */
35static s64 time_offset; /* time adjustment (ns) */
36static long time_constant = 2; /* pll time constant */
37long time_maxerror = NTP_PHASE_LIMIT; /* maximum error (us) */
38long time_esterror = NTP_PHASE_LIMIT; /* estimated error (us) */
39long time_freq; /* frequency offset (scaled ppm)*/
40static long time_reftime; /* time at last adjustment (s) */
41long time_adjust;
42
43#define CLOCK_TICK_OVERFLOW (LATCH * HZ - CLOCK_TICK_RATE)
44#define CLOCK_TICK_ADJUST (((s64)CLOCK_TICK_OVERFLOW * NSEC_PER_SEC) / \
45 (s64)CLOCK_TICK_RATE)
46
47static void ntp_update_frequency(void)
48{
49 u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
50 << TICK_LENGTH_SHIFT;
51 second_length += (s64)CLOCK_TICK_ADJUST << TICK_LENGTH_SHIFT;
52 second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC);
53
54 tick_length_base = second_length;
55
56 do_div(second_length, HZ);
57 tick_nsec = second_length >> TICK_LENGTH_SHIFT;
58
59 do_div(tick_length_base, NTP_INTERVAL_FREQ);
60}
61
62/**
63 * ntp_clear - Clears the NTP state variables
64 *
65 * Must be called while holding a write on the xtime_lock
66 */
67void ntp_clear(void)
68{
69 time_adjust = 0; /* stop active adjtime() */
70 time_status |= STA_UNSYNC;
71 time_maxerror = NTP_PHASE_LIMIT;
72 time_esterror = NTP_PHASE_LIMIT;
73
74 ntp_update_frequency();
75
76 tick_length = tick_length_base;
77 time_offset = 0;
78}
79
80/*
81 * this routine handles the overflow of the microsecond field
82 *
83 * The tricky bits of code to handle the accurate clock support
84 * were provided by Dave Mills ([email protected]) of NTP fame.
85 * They were originally developed for SUN and DEC kernels.
86 * All the kudos should go to Dave for this stuff.
87 */
88void second_overflow(void)
89{
90 long time_adj;
91
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;
97 }
98
99 /*
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.
105 */
106 switch (time_state) {
107 case TIME_OK:
108 if (time_status & STA_INS)
109 time_state = TIME_INS;
110 else if (time_status & STA_DEL)
111 time_state = TIME_DEL;
112 break;
113 case TIME_INS:
114 if (xtime.tv_sec % 86400 == 0) {
115 xtime.tv_sec--;
116 wall_to_monotonic.tv_sec++;
117 /*
118 * The timer interpolator will make time change
119 * gradually instead of an immediate jump by one second
120 */
121 time_interpolator_update(-NSEC_PER_SEC);
122 time_state = TIME_OOP;
123 clock_was_set();
124 printk(KERN_NOTICE "Clock: inserting leap second "
125 "23:59:60 UTC\n");
126 }
127 break;
128 case TIME_DEL:
129 if ((xtime.tv_sec + 1) % 86400 == 0) {
130 xtime.tv_sec++;
131 wall_to_monotonic.tv_sec--;
132 /*
133 * Use of time interpolator for a gradual change of
134 * time
135 */
136 time_interpolator_update(NSEC_PER_SEC);
137 time_state = TIME_WAIT;
138 clock_was_set();
139 printk(KERN_NOTICE "Clock: deleting leap second "
140 "23:59:59 UTC\n");
141 }
142 break;
143 case TIME_OOP:
144 time_state = TIME_WAIT;
145 break;
146 case TIME_WAIT:
147 if (!(time_status & (STA_INS | STA_DEL)))
148 time_state = TIME_OK;
149 }
150
151 /*
152 * Compute the phase adjustment for the next second. The offset is
153 * reduced by a fixed factor times the time constant.
154 */
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);
159
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;
167 } else {
168 tick_length += (s64)(time_adjust * NSEC_PER_USEC /
169 NTP_INTERVAL_FREQ) << TICK_LENGTH_SHIFT;
170 time_adjust = 0;
171 }
172 }
173}
174
175/*
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.
182 */
183u64 current_tick_length(void)
184{
185 return tick_length;
186}
187
188
189void __attribute__ ((weak)) notify_arch_cmos_timer(void)
190{
191 return;
192}
193
194/* adjtimex mainly allows reading (and writing, if superuser) of
195 * kernel time-keeping variables. used by xntpd.
196 */
197int do_adjtimex(struct timex *txc)
198{
199 long mtemp, save_adjust, rem;
200 s64 freq_adj, temp64;
201 int result;
202
203 /* In order to modify anything, you gotta be super-user! */
204 if (txc->modes && !capable(CAP_SYS_TIME))
205 return -EPERM;
206
207 /* Now we validate the data before disabling interrupts */
208
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)
212 return -EINVAL;
213
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 )
217 return -EINVAL;
218
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)
223 return -EINVAL;
224
225 write_seqlock_irq(&xtime_lock);
226 result = time_state; /* mostly `TIME_OK' */
227
228 /* Save for later - semantics of adjtime is to return old value */
229 save_adjust = time_adjust;
230
231#if 0 /* STA_CLOCKERR is never set yet */
232 time_status &= ~STA_CLOCKERR; /* reset STA_CLOCKERR */
233#endif
234 /* If there are input parameters, then process them */
235 if (txc->modes)
236 {
237 if (txc->modes & ADJ_STATUS) /* only set allowed bits */
238 time_status = (txc->status & ~STA_RONLY) |
239 (time_status & STA_RONLY);
240
241 if (txc->modes & ADJ_FREQUENCY) { /* p. 22 */
242 if (txc->freq > MAXFREQ || txc->freq < -MAXFREQ) {
243 result = -EINVAL;
244 goto leave;
245 }
246 time_freq = ((s64)txc->freq * NSEC_PER_USEC)
247 >> (SHIFT_USEC - SHIFT_NSEC);
248 }
249
250 if (txc->modes & ADJ_MAXERROR) {
251 if (txc->maxerror < 0 || txc->maxerror >= NTP_PHASE_LIMIT) {
252 result = -EINVAL;
253 goto leave;
254 }
255 time_maxerror = txc->maxerror;
256 }
257
258 if (txc->modes & ADJ_ESTERROR) {
259 if (txc->esterror < 0 || txc->esterror >= NTP_PHASE_LIMIT) {
260 result = -EINVAL;
261 goto leave;
262 }
263 time_esterror = txc->esterror;
264 }
265
266 if (txc->modes & ADJ_TIMECONST) { /* p. 24 */
267 if (txc->constant < 0) { /* NTP v4 uses values > 6 */
268 result = -EINVAL;
269 goto leave;
270 }
271 time_constant = min(txc->constant + 4, (long)MAXTC);
272 }
273
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;
278 }
279 else if (time_status & STA_PLL) {
280 time_offset = txc->offset * NSEC_PER_USEC;
281
282 /*
283 * Scale the phase adjustment and
284 * clamp to the operating range.
285 */
286 time_offset = min(time_offset, (s64)MAXPHASE * NSEC_PER_USEC);
287 time_offset = max(time_offset, (s64)-MAXPHASE * NSEC_PER_USEC);
288
289 /*
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.
293 */
294
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;
299
300 freq_adj = 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 = time_offset << (SHIFT_NSEC - SHIFT_FLL);
305 if (time_offset < 0) {
306 temp64 = -temp64;
307 do_div(temp64, mtemp);
308 freq_adj -= temp64;
309 } else {
310 do_div(temp64, mtemp);
311 freq_adj += temp64;
312 }
313 }
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 = div_long_long_rem_signed(time_offset,
318 NTP_INTERVAL_FREQ,
319 &rem);
320 time_offset <<= SHIFT_UPDATE;
321 } /* STA_PLL */
322 } /* txc->modes & ADJ_OFFSET */
323 if (txc->modes & ADJ_TICK)
324 tick_usec = txc->tick;
325
326 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
327 ntp_update_frequency();
328 } /* txc->modes */
329leave: if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
330 result = TIME_ERROR;
331
332 if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
333 txc->offset = save_adjust;
334 else
335 txc->offset = ((long)shift_right(time_offset, SHIFT_UPDATE)) *
336 NTP_INTERVAL_FREQ / 1000;
337 txc->freq = (time_freq / NSEC_PER_USEC) <<
338 (SHIFT_USEC - SHIFT_NSEC);
339 txc->maxerror = time_maxerror;
340 txc->esterror = time_esterror;
341 txc->status = time_status;
342 txc->constant = time_constant;
343 txc->precision = 1;
344 txc->tolerance = MAXFREQ;
345 txc->tick = tick_usec;
346
347 /* PPS is not implemented, so these are zero */
348 txc->ppsfreq = 0;
349 txc->jitter = 0;
350 txc->shift = 0;
351 txc->stabil = 0;
352 txc->jitcnt = 0;
353 txc->calcnt = 0;
354 txc->errcnt = 0;
355 txc->stbcnt = 0;
356 write_sequnlock_irq(&xtime_lock);
357 do_gettimeofday(&txc->time);
358 notify_arch_cmos_timer();
359 return(result);
360}