1 /* vi: set sw=4 ts=4: */
3 * Mini hwclock implementation for busybox
5 * Copyright (C) 2002 Robert Griebl <griebl@gmx.de>
7 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
11 /* After libbb.h, since it needs sys/types.h on some systems */
12 #include <sys/utsname.h>
15 /* diff code is disabled: it's not sys/hw clock diff, it's some useless
16 * "time between hwclock was started and we saw CMOS tick" quantity.
17 * It's useless since hwclock is started at a random moment,
18 * thus the quantity is also random, useless. Showing 0.000000 does not
19 * deprive us from any useful info.
21 * SHOW_HWCLOCK_DIFF code in this file shows the difference between system
22 * and hw clock. It is useful, but not compatible with standard hwclock.
25 #define SHOW_HWCLOCK_DIFF 0
28 #if !SHOW_HWCLOCK_DIFF
29 # define read_rtc(pp_rtcname, sys_tv, utc) read_rtc(pp_rtcname, utc)
31 static time_t read_rtc(const char **pp_rtcname
, struct timeval
*sys_tv
, int utc
)
36 fd
= rtc_xopen(pp_rtcname
, O_RDONLY
);
38 rtc_read_tm(&tm_time
, fd
);
42 int before
= tm_time
.tm_sec
;
44 rtc_read_tm(&tm_time
, fd
);
45 gettimeofday(sys_tv
, NULL
);
46 if (before
!= tm_time
.tm_sec
)
52 if (ENABLE_FEATURE_CLEAN_UP
)
55 return rtc_tm2time(&tm_time
, utc
);
58 static void show_clock(const char **pp_rtcname
, int utc
)
61 struct timeval sys_tv
;
66 t
= read_rtc(pp_rtcname
, &sys_tv
, utc
);
68 strchrnul(cp
, '\n')[0] = '\0';
69 #if !SHOW_HWCLOCK_DIFF
70 printf("%s 0.000000 seconds\n", cp
);
73 long diff
= sys_tv
.tv_sec
- t
;
74 if (diff
< 0 /*&& tv.tv_usec != 0*/) {
76 /* diff >= 0 is ok: diff < 0, can't just use tv.tv_usec: */
77 /* 45.520820 43.520820 */
78 /* - 44.000000 - 45.000000 */
79 /* = 1.520820 = -1.479180, not -2.520820! */
81 /* should be 1000000 - tv.tv_usec, but then we must check tv.tv_usec != 0 */
82 sys_tv
.tv_usec
= 999999 - sys_tv
.tv_usec
;
84 printf("%s %ld.%06lu seconds\n", cp
, diff
, (unsigned long)sys_tv
.tv_usec
);
89 static void to_sys_clock(const char **pp_rtcname
, int utc
)
94 tz
.tz_minuteswest
= timezone
/60 - 60*daylight
;
97 tv
.tv_sec
= read_rtc(pp_rtcname
, NULL
, utc
);
99 if (settimeofday(&tv
, &tz
))
100 bb_perror_msg_and_die("settimeofday");
103 static void from_sys_clock(const char **pp_rtcname
, int utc
)
110 rtc
= rtc_xopen(pp_rtcname
, O_WRONLY
);
111 gettimeofday(&tv
, NULL
);
112 /* Prepare tm_time */
113 if (sizeof(time_t) == sizeof(tv
.tv_sec
)) {
115 gmtime_r((time_t*)&tv
.tv_sec
, &tm_time
);
117 localtime_r((time_t*)&tv
.tv_sec
, &tm_time
);
119 time_t t
= tv
.tv_sec
;
121 gmtime_r(&t
, &tm_time
);
123 localtime_r(&t
, &tm_time
);
126 /* Bloated code which tries to set hw clock with better precision.
127 * On x86, even though code does set hw clock within <1ms of exact
128 * whole seconds, apparently hw clock (at least on some machines)
129 * doesn't reset internal fractional seconds to 0,
130 * making all this a pointless excercise.
132 /* If we see that we are N usec away from whole second,
133 * we'll sleep for N-ADJ usecs. ADJ corrects for the fact
134 * that CPU is not infinitely fast.
135 * On infinitely fast CPU, next wakeup would be
136 * on (exactly_next_whole_second - ADJ). On real CPUs,
137 * this difference between current time and whole second
138 * is less than ADJ (assuming system isn't heavily loaded).
140 /* Small value of 256us gives very precise sync for 2+ GHz CPUs.
141 * Slower CPUs will fail to sync and will go to bigger
142 * ADJ values. qemu-emulated armv4tl with ~100 MHz
143 * performance ends up using ADJ ~= 4*1024 and it takes
144 * 2+ secs (2 tries with successively larger ADJ)
145 * to sync. Even straced one on the same qemu (very slow)
146 * takes only 4 tries.
148 #define TWEAK_USEC 256
149 unsigned adj
= TWEAK_USEC
;
152 int rtc
= rtc_xopen(pp_rtcname
, O_WRONLY
);
154 /* Try to catch the moment when whole second is close */
159 gettimeofday(&tv
, NULL
);
162 rem_usec
= 1000000 - tv
.tv_usec
;
163 if (rem_usec
< adj
) {
169 /* Prepare tm_time from t */
171 gmtime_r(&t
, &tm_time
); /* may read /etc/xxx (it takes time) */
173 localtime_r(&t
, &tm_time
); /* same */
175 if (adj
>= 32*1024) {
176 break; /* 32 ms diff and still no luck?? give up trying to sync */
179 /* gmtime/localtime took some time, re-get cur time */
180 gettimeofday(&tv
, NULL
);
182 if (tv
.tv_sec
< t
/* we are still in old second */
183 || (tv
.tv_sec
== t
&& tv
.tv_usec
< adj
) /* not too far into next second */
185 break; /* good, we are in sync! */
188 rem_usec
= 1000000 - tv
.tv_usec
;
189 if (rem_usec
< adj
) {
191 goto small_rem
; /* already close to next sec, don't sleep */
194 /* Try to sync up by sleeping */
195 usleep(rem_usec
- adj
);
197 /* Jump to 1ms diff, then increase fast (x2): EVERY loop
198 * takes ~1 sec, people won't like slowly converging code here!
200 //bb_error_msg("adj:%d tv.tv_usec:%d", adj, (int)tv.tv_usec);
203 /* ... and if last "overshoot" does not look insanely big,
204 * just use it as adj increment. This makes convergence faster.
206 if (tv
.tv_usec
< adj
* 8) {
212 /* Debug aid to find "optimal" TWEAK_USEC with nearly exact sync.
213 * Look for a value which makes tv_usec close to 999999 or 0.
214 * For 2.20GHz Intel Core 2: optimal TWEAK_USEC ~= 200
216 //bb_error_msg("tv.tv_usec:%d", (int)tv.tv_usec);
219 tm_time
.tm_isdst
= 0;
220 xioctl(rtc
, RTC_SET_TIME
, &tm_time
);
222 if (ENABLE_FEATURE_CLEAN_UP
)
226 #define HWCLOCK_OPT_LOCALTIME 0x01
227 #define HWCLOCK_OPT_UTC 0x02
228 #define HWCLOCK_OPT_SHOW 0x04
229 #define HWCLOCK_OPT_HCTOSYS 0x08
230 #define HWCLOCK_OPT_SYSTOHC 0x10
231 #define HWCLOCK_OPT_RTCFILE 0x20
233 int hwclock_main(int argc
, char **argv
) MAIN_EXTERNALLY_VISIBLE
;
234 int hwclock_main(int argc UNUSED_PARAM
, char **argv
)
236 const char *rtcname
= NULL
;
240 #if ENABLE_FEATURE_HWCLOCK_LONG_OPTIONS
241 static const char hwclock_longopts
[] ALIGN1
=
242 "localtime\0" No_argument
"l"
243 "utc\0" No_argument
"u"
244 "show\0" No_argument
"r"
245 "hctosys\0" No_argument
"s"
246 "systohc\0" No_argument
"w"
247 "file\0" Required_argument
"f"
249 applet_long_options
= hwclock_longopts
;
251 opt_complementary
= "r--ws:w--rs:s--wr:l--u:u--l";
252 opt
= getopt32(argv
, "lurswf:", &rtcname
);
254 /* If -u or -l wasn't given check if we are using utc */
255 if (opt
& (HWCLOCK_OPT_UTC
| HWCLOCK_OPT_LOCALTIME
))
256 utc
= (opt
& HWCLOCK_OPT_UTC
);
258 utc
= rtc_adjtime_is_utc();
260 if (opt
& HWCLOCK_OPT_HCTOSYS
)
261 to_sys_clock(&rtcname
, utc
);
262 else if (opt
& HWCLOCK_OPT_SYSTOHC
)
263 from_sys_clock(&rtcname
, utc
);
265 /* default HWCLOCK_OPT_SHOW */
266 show_clock(&rtcname
, utc
);