source: branches/3.2/mindi-busybox/util-linux/hwclock.c @ 3186

Last change on this file since 3186 was 2725, checked in by bruno, 8 years ago
  • Update mindi-busybox to 1.18.3 to avoid problems with the tar command which is now failing on recent versions with busybox 1.7.3
File size: 7.0 KB
Line 
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
31static 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
58static 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
89static 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
103static 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
233int hwclock_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
234int 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}
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