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 tarball for details.
11 /* After libbb.h, since it needs sys/types.h on some systems */
12 #include <sys/utsname.h>
15 #if ENABLE_FEATURE_HWCLOCK_LONG_OPTIONS
22 /* diff code is disabled: it's not sys/hw clock diff, it's some useless
23 * "time between hwclock was started and we saw CMOS tick" quantity.
24 * It's useless since hwclock is started at a random moment,
25 * thus the quantity is also random, useless. Showing 0.000000 does not
26 * deprive us from any useful info.
28 * SHOW_HWCLOCK_DIFF code in this file shows the difference between system
29 * and hw clock. It is useful, but not compatible with standard hwclock.
32 #define SHOW_HWCLOCK_DIFF 0
35 #if !SHOW_HWCLOCK_DIFF
36 # define read_rtc(pp_rtcname, sys_tv, utc) read_rtc(pp_rtcname, utc)
38 static time_t read_rtc(const char **pp_rtcname, struct timeval *sys_tv, int utc)
43 fd = rtc_xopen(pp_rtcname, O_RDONLY);
45 rtc_read_tm(&tm_time, fd);
49 int before = tm_time.tm_sec;
51 rtc_read_tm(&tm_time, fd);
52 gettimeofday(sys_tv, NULL);
53 if (before != tm_time.tm_sec)
59 if (ENABLE_FEATURE_CLEAN_UP)
62 return rtc_tm2time(&tm_time, utc);
65 static void show_clock(const char **pp_rtcname, int utc)
68 struct timeval sys_tv;
73 t = read_rtc(pp_rtcname, &sys_tv, utc);
75 strchrnul(cp, '\n')[0] = '\0';
76 #if !SHOW_HWCLOCK_DIFF
77 printf("%s 0.000000 seconds\n", cp);
80 long diff = sys_tv.tv_sec - t;
81 if (diff < 0 /*&& tv.tv_usec != 0*/) {
83 /* diff >= 0 is ok: diff < 0, can't just use tv.tv_usec: */
84 /* 45.520820 43.520820 */
85 /* - 44.000000 - 45.000000 */
86 /* = 1.520820 = -1.479180, not -2.520820! */
88 /* should be 1000000 - tv.tv_usec, but then we must check tv.tv_usec != 0 */
89 sys_tv.tv_usec = 999999 - sys_tv.tv_usec;
91 printf("%s %ld.%06lu seconds\n", cp, diff, (unsigned long)sys_tv.tv_usec);
96 static void to_sys_clock(const char **pp_rtcname, int utc)
101 tz.tz_minuteswest = timezone/60 - 60*daylight;
104 tv.tv_sec = read_rtc(pp_rtcname, NULL, utc);
106 if (settimeofday(&tv, &tz))
107 bb_perror_msg_and_die("settimeofday");
110 static void from_sys_clock(const char **pp_rtcname, int utc)
117 rtc = rtc_xopen(pp_rtcname, O_WRONLY);
118 gettimeofday(&tv, NULL);
119 /* Prepare tm_time */
120 if (sizeof(time_t) == sizeof(tv.tv_sec)) {
122 gmtime_r((time_t*)&tv.tv_sec, &tm_time);
124 localtime_r((time_t*)&tv.tv_sec, &tm_time);
126 time_t t = tv.tv_sec;
128 gmtime_r(&t, &tm_time);
130 localtime_r(&t, &tm_time);
133 /* Bloated code which tries to set hw clock with better precision.
134 * On x86, even though code does set hw clock within <1ms of exact
135 * whole seconds, apparently hw clock (at least on some machines)
136 * doesn't reset internal fractional seconds to 0,
137 * making all this a pointless excercise.
139 /* If we see that we are N usec away from whole second,
140 * we'll sleep for N-ADJ usecs. ADJ corrects for the fact
141 * that CPU is not infinitely fast.
142 * On infinitely fast CPU, next wakeup would be
143 * on (exactly_next_whole_second - ADJ). On real CPUs,
144 * this difference between current time and whole second
145 * is less than ADJ (assuming system isn't heavily loaded).
147 /* Small value of 256us gives very precise sync for 2+ GHz CPUs.
148 * Slower CPUs will fail to sync and will go to bigger
149 * ADJ values. qemu-emulated armv4tl with ~100 MHz
150 * performance ends up using ADJ ~= 4*1024 and it takes
151 * 2+ secs (2 tries with successively larger ADJ)
152 * to sync. Even straced one on the same qemu (very slow)
153 * takes only 4 tries.
155 #define TWEAK_USEC 256
156 unsigned adj = TWEAK_USEC;
159 int rtc = rtc_xopen(pp_rtcname, O_WRONLY);
161 /* Try to catch the moment when whole second is close */
166 gettimeofday(&tv, NULL);
169 rem_usec = 1000000 - tv.tv_usec;
170 if (rem_usec < adj) {
176 /* Prepare tm_time from t */
178 gmtime_r(&t, &tm_time); /* may read /etc/xxx (it takes time) */
180 localtime_r(&t, &tm_time); /* same */
182 if (adj >= 32*1024) {
183 break; /* 32 ms diff and still no luck?? give up trying to sync */
186 /* gmtime/localtime took some time, re-get cur time */
187 gettimeofday(&tv, NULL);
189 if (tv.tv_sec < t /* we are still in old second */
190 || (tv.tv_sec == t && tv.tv_usec < adj) /* not too far into next second */
192 break; /* good, we are in sync! */
195 rem_usec = 1000000 - tv.tv_usec;
196 if (rem_usec < adj) {
198 goto small_rem; /* already close to next sec, don't sleep */
201 /* Try to sync up by sleeping */
202 usleep(rem_usec - adj);
204 /* Jump to 1ms diff, then increase fast (x2): EVERY loop
205 * takes ~1 sec, people won't like slowly converging code here!
207 //bb_error_msg("adj:%d tv.tv_usec:%d", adj, (int)tv.tv_usec);
210 /* ... and if last "overshoot" does not look insanely big,
211 * just use it as adj increment. This makes convergence faster.
213 if (tv.tv_usec < adj * 8) {
219 /* Debug aid to find "optimal" TWEAK_USEC with nearly exact sync.
220 * Look for a value which makes tv_usec close to 999999 or 0.
221 * For 2.20GHz Intel Core 2: optimal TWEAK_USEC ~= 200
223 //bb_error_msg("tv.tv_usec:%d", (int)tv.tv_usec);
226 tm_time.tm_isdst = 0;
227 xioctl(rtc, RTC_SET_TIME, &tm_time);
229 if (ENABLE_FEATURE_CLEAN_UP)
233 #define HWCLOCK_OPT_LOCALTIME 0x01
234 #define HWCLOCK_OPT_UTC 0x02
235 #define HWCLOCK_OPT_SHOW 0x04
236 #define HWCLOCK_OPT_HCTOSYS 0x08
237 #define HWCLOCK_OPT_SYSTOHC 0x10
238 #define HWCLOCK_OPT_RTCFILE 0x20
240 int hwclock_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
241 int hwclock_main(int argc UNUSED_PARAM, char **argv)
243 const char *rtcname = NULL;
247 #if ENABLE_FEATURE_HWCLOCK_LONG_OPTIONS
248 static const char hwclock_longopts[] ALIGN1 =
249 "localtime\0" No_argument "l"
250 "utc\0" No_argument "u"
251 "show\0" No_argument "r"
252 "hctosys\0" No_argument "s"
253 "systohc\0" No_argument "w"
254 "file\0" Required_argument "f"
256 applet_long_options = hwclock_longopts;
258 opt_complementary = "r--ws:w--rs:s--wr:l--u:u--l";
259 opt = getopt32(argv, "lurswf:", &rtcname);
261 /* If -u or -l wasn't given check if we are using utc */
262 if (opt & (HWCLOCK_OPT_UTC | HWCLOCK_OPT_LOCALTIME))
263 utc = (opt & HWCLOCK_OPT_UTC);
265 utc = rtc_adjtime_is_utc();
267 if (opt & HWCLOCK_OPT_HCTOSYS)
268 to_sys_clock(&rtcname, utc);
269 else if (opt & HWCLOCK_OPT_SYSTOHC)
270 from_sys_clock(&rtcname, utc);
272 /* default HWCLOCK_OPT_SHOW */
273 show_clock(&rtcname, utc);