release/src/router/busybox/util-linux/hwclock.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Mini hwclock implementation for busybox
   4  *
   5  * Copyright (C) 2002 Robert Griebl <griebl@gmx.de>
   6  *
   7  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   8 */
   9
  10 #include "libbb.h"
  11 /* After libbb.h, since it needs sys/types.h on some systems */
  12 #include <sys/utsname.h>
  13 #include "rtc_.h"
  14
  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.
  20  *
  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.
  23  * Thus disabled.
  24  */
  25 #define SHOW_HWCLOCK_DIFF 0
  26
  27
  28 #if !SHOW_HWCLOCK_DIFF
  29 # define read_rtc(pp_rtcname, sys_tv, utc) read_rtc(pp_rtcname, utc)
  30 #endif
  31 static time_t read_rtc(const char **pp_rtcname, struct timeval *sys_tv, int utc)
  32 {
  33         struct tm tm_time;
  34         int fd;
  35
  36         fd = rtc_xopen(pp_rtcname, O_RDONLY);
  37
  38         rtc_read_tm(&tm_time, fd);
  39
  40 #if SHOW_HWCLOCK_DIFF
  41         {
  42                 int before = tm_time.tm_sec;
  43                 while (1) {
  44                         rtc_read_tm(&tm_time, fd);
  45                         gettimeofday(sys_tv, NULL);
  46                         if (before != tm_time.tm_sec)
  47                                 break;
  48                 }
  49         }
  50 #endif
  51
  52         if (ENABLE_FEATURE_CLEAN_UP)
  53                 close(fd);
  54
  55         return rtc_tm2time(&tm_time, utc);
  56 }
  57
  58 static void show_clock(const char **pp_rtcname, int utc)
  59 {
  60 #if SHOW_HWCLOCK_DIFF
  61         struct timeval sys_tv;
  62 #endif
  63         time_t t;
  64         char *cp;
  65
  66         t = read_rtc(pp_rtcname, &sys_tv, utc);
  67         cp = ctime(&t);
  68         strchrnul(cp, '\n')[0] = '\0';
  69 #if !SHOW_HWCLOCK_DIFF
  70         printf("%s  0.000000 seconds\n", cp);
  71 #else
  72         {
  73                 long diff = sys_tv.tv_sec - t;
  74                 if (diff < 0 /*&& tv.tv_usec != 0*/) {
  75                         /* Why? */
  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! */
  80                         diff++;
  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;
  83                 }
  84                 printf("%s  %ld.%06lu seconds\n", cp, diff, (unsigned long)sys_tv.tv_usec);
  85         }
  86 #endif
  87 }
  88
  89 static void to_sys_clock(const char **pp_rtcname, int utc)
  90 {
  91         struct timeval tv;
  92         struct timezone tz;
  93
  94         tz.tz_minuteswest = timezone/60 - 60*daylight;
  95         tz.tz_dsttime = 0;
  96
  97         tv.tv_sec = read_rtc(pp_rtcname, NULL, utc);
  98         tv.tv_usec = 0;
  99         if (settimeofday(&tv, &tz))
 100                 bb_perror_msg_and_die("settimeofday");
 101 }
 102
 103 static void from_sys_clock(const char **pp_rtcname, int utc)
 104 {
 105 #if 1
 106         struct timeval tv;
 107         struct tm tm_time;
 108         int rtc;
 109
 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)) {
 114                 if (utc)
 115                         gmtime_r((time_t*)&tv.tv_sec, &tm_time);
 116                 else
 117                         localtime_r((time_t*)&tv.tv_sec, &tm_time);
 118         } else {
 119                 time_t t = tv.tv_sec;
 120                 if (utc)
 121                         gmtime_r(&t, &tm_time);
 122                 else
 123                         localtime_r(&t, &tm_time);
 124         }
 125 #else
 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.
 131  */
 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).
 139          */
 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.
 147          */
 148 #define TWEAK_USEC 256
 149         unsigned adj = TWEAK_USEC;
 150         struct tm tm_time;
 151         struct timeval tv;
 152         int rtc = rtc_xopen(pp_rtcname, O_WRONLY);
 153
 154         /* Try to catch the moment when whole second is close */
 155         while (1) {
 156                 unsigned rem_usec;
 157                 time_t t;
 158
 159                 gettimeofday(&tv, NULL);
 160
 161                 t = tv.tv_sec;
 162                 rem_usec = 1000000 - tv.tv_usec;
 163                 if (rem_usec < adj) {
 164                         /* Close enough */
 165  small_rem:
 166                         t++;
 167                 }
 168
 169                 /* Prepare tm_time from t */
 170                 if (utc)
 171                         gmtime_r(&t, &tm_time); /* may read /etc/xxx (it takes time) */
 172                 else
 173                         localtime_r(&t, &tm_time); /* same */
 174
 175                 if (adj >= 32*1024) {
 176                         break; /* 32 ms diff and still no luck?? give up trying to sync */
 177                 }
 178
 179                 /* gmtime/localtime took some time, re-get cur time */
 180                 gettimeofday(&tv, NULL);
 181
 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 */
 184                 ) {
 185                         break; /* good, we are in sync! */
 186                 }
 187
 188                 rem_usec = 1000000 - tv.tv_usec;
 189                 if (rem_usec < adj) {
 190                         t = tv.tv_sec;
 191                         goto small_rem; /* already close to next sec, don't sleep */
 192                 }
 193
 194                 /* Try to sync up by sleeping */
 195                 usleep(rem_usec - adj);
 196
 197                 /* Jump to 1ms diff, then increase fast (x2): EVERY loop
 198                  * takes ~1 sec, people won't like slowly converging code here!
 199                  */
 200         //bb_error_msg("adj:%d tv.tv_usec:%d", adj, (int)tv.tv_usec);
 201                 if (adj < 512)
 202                         adj = 512;
 203                 /* ... and if last "overshoot" does not look insanely big,
 204                  * just use it as adj increment. This makes convergence faster.
 205                  */
 206                 if (tv.tv_usec < adj * 8) {
 207                         adj += tv.tv_usec;
 208                         continue;
 209                 }
 210                 adj *= 2;
 211         }
 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
 215          */
 216         //bb_error_msg("tv.tv_usec:%d", (int)tv.tv_usec);
 217 #endif
 218
 219         tm_time.tm_isdst = 0;
 220         xioctl(rtc, RTC_SET_TIME, &tm_time);
 221
 222         if (ENABLE_FEATURE_CLEAN_UP)
 223                 close(rtc);
 224 }
 225
 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
 232
 233 int hwclock_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 234 int hwclock_main(int argc UNUSED_PARAM, char **argv)
 235 {
 236         const char *rtcname = NULL;
 237         unsigned opt;
 238         int utc;
 239
 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"
 248                 ;
 249         applet_long_options = hwclock_longopts;
 250 #endif
 251         opt_complementary = "r--ws:w--rs:s--wr:l--u:u--l";
 252         opt = getopt32(argv, "lurswf:", &rtcname);
 253
 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);
 257         else
 258                 utc = rtc_adjtime_is_utc();
 259
 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);
 264         else
 265                 /* default HWCLOCK_OPT_SHOW */
 266                 show_clock(&rtcname, utc);
 267
 268         return 0;
 269 }