source: MondoRescue/branches/2.2.9/mindi-busybox/util-linux/hwclock.c@ 2725

/* vi: set sw=4 ts=4: */
/*
 * Mini hwclock implementation for busybox
 *
 * Copyright (C) 2002 Robert Griebl <griebl@gmx.de>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
*/

#include "libbb.h"
/* After libbb.h, since it needs sys/types.h on some systems */
#include <sys/utsname.h>
#include "rtc_.h"

/* diff code is disabled: it's not sys/hw clock diff, it's some useless
 * "time between hwclock was started and we saw CMOS tick" quantity.
 * It's useless since hwclock is started at a random moment,
 * thus the quantity is also random, useless. Showing 0.000000 does not
 * deprive us from any useful info.
 *
 * SHOW_HWCLOCK_DIFF code in this file shows the difference between system
 * and hw clock. It is useful, but not compatible with standard hwclock.
 * Thus disabled.
 */
#define SHOW_HWCLOCK_DIFF 0


#if !SHOW_HWCLOCK_DIFF
# define read_rtc(pp_rtcname, sys_tv, utc) read_rtc(pp_rtcname, utc)
#endif
static time_t read_rtc(const char **pp_rtcname, struct timeval *sys_tv, int utc)
{
    struct tm tm_time;
    int fd;

    fd = rtc_xopen(pp_rtcname, O_RDONLY);

    rtc_read_tm(&tm_time, fd);

#if SHOW_HWCLOCK_DIFF
    {
        int before = tm_time.tm_sec;
        while (1) {
            rtc_read_tm(&tm_time, fd);
            gettimeofday(sys_tv, NULL);
            if (before != tm_time.tm_sec)
                break;
        }
    }
#endif

    if (ENABLE_FEATURE_CLEAN_UP)
        close(fd);

    return rtc_tm2time(&tm_time, utc);
}

static void show_clock(const char **pp_rtcname, int utc)
{
#if SHOW_HWCLOCK_DIFF
    struct timeval sys_tv;
#endif
    time_t t;
    char *cp;

    t = read_rtc(pp_rtcname, &sys_tv, utc);
    cp = ctime(&t);
    strchrnul(cp, '\n')[0] = '\0';
#if !SHOW_HWCLOCK_DIFF
    printf("%s  0.000000 seconds\n", cp);
#else
    {
        long diff = sys_tv.tv_sec - t;
        if (diff < 0 /*&& tv.tv_usec != 0*/) {
            /* Why? */
            /* diff >= 0 is ok:   diff < 0, can't just use tv.tv_usec: */
            /*   45.520820          43.520820 */
            /* - 44.000000        - 45.000000 */
            /* =  1.520820        = -1.479180, not -2.520820! */
            diff++;
            /* should be 1000000 - tv.tv_usec, but then we must check tv.tv_usec != 0 */
            sys_tv.tv_usec = 999999 - sys_tv.tv_usec;
        }
        printf("%s  %ld.%06lu seconds\n", cp, diff, (unsigned long)sys_tv.tv_usec);
    }
#endif
}

static void to_sys_clock(const char **pp_rtcname, int utc)
{
    struct timeval tv;
    struct timezone tz;

    tz.tz_minuteswest = timezone/60 - 60*daylight;
    tz.tz_dsttime = 0;

    tv.tv_sec = read_rtc(pp_rtcname, NULL, utc);
    tv.tv_usec = 0;
    if (settimeofday(&tv, &tz))
        bb_perror_msg_and_die("settimeofday");
}

static void from_sys_clock(const char **pp_rtcname, int utc)
{
#if 1
    struct timeval tv;
    struct tm tm_time;
    int rtc;

    rtc = rtc_xopen(pp_rtcname, O_WRONLY);
    gettimeofday(&tv, NULL);
    /* Prepare tm_time */
    if (sizeof(time_t) == sizeof(tv.tv_sec)) {
        if (utc)
            gmtime_r((time_t*)&tv.tv_sec, &tm_time);
        else
            localtime_r((time_t*)&tv.tv_sec, &tm_time);
    } else {
        time_t t = tv.tv_sec;
        if (utc)
            gmtime_r(&t, &tm_time);
        else
            localtime_r(&t, &tm_time);
    }
#else
/* Bloated code which tries to set hw clock with better precision.
 * On x86, even though code does set hw clock within <1ms of exact
 * whole seconds, apparently hw clock (at least on some machines)
 * doesn't reset internal fractional seconds to 0,
 * making all this a pointless excercise.
 */
    /* If we see that we are N usec away from whole second,
     * we'll sleep for N-ADJ usecs. ADJ corrects for the fact
     * that CPU is not infinitely fast.
     * On infinitely fast CPU, next wakeup would be
     * on (exactly_next_whole_second - ADJ). On real CPUs,
     * this difference between current time and whole second
     * is less than ADJ (assuming system isn't heavily loaded).
     */
    /* Small value of 256us gives very precise sync for 2+ GHz CPUs.
     * Slower CPUs will fail to sync and will go to bigger
     * ADJ values. qemu-emulated armv4tl with ~100 MHz
     * performance ends up using ADJ ~= 4*1024 and it takes
     * 2+ secs (2 tries with successively larger ADJ)
     * to sync. Even straced one on the same qemu (very slow)
     * takes only 4 tries.
     */
#define TWEAK_USEC 256
    unsigned adj = TWEAK_USEC;
    struct tm tm_time;
    struct timeval tv;
    int rtc = rtc_xopen(pp_rtcname, O_WRONLY);

    /* Try to catch the moment when whole second is close */
    while (1) {
        unsigned rem_usec;
        time_t t;

        gettimeofday(&tv, NULL);

        t = tv.tv_sec;
        rem_usec = 1000000 - tv.tv_usec;
        if (rem_usec < adj) {
            /* Close enough */
 small_rem:
            t++;
        }

        /* Prepare tm_time from t */
        if (utc)
            gmtime_r(&t, &tm_time); /* may read /etc/xxx (it takes time) */
        else
            localtime_r(&t, &tm_time); /* same */

        if (adj >= 32*1024) {
            break; /* 32 ms diff and still no luck?? give up trying to sync */
        }

        /* gmtime/localtime took some time, re-get cur time */
        gettimeofday(&tv, NULL);

        if (tv.tv_sec < t /* we are still in old second */
         || (tv.tv_sec == t && tv.tv_usec < adj) /* not too far into next second */
        ) {
            break; /* good, we are in sync! */
        }

        rem_usec = 1000000 - tv.tv_usec;
        if (rem_usec < adj) {
            t = tv.tv_sec;
            goto small_rem; /* already close to next sec, don't sleep */
        }

        /* Try to sync up by sleeping */
        usleep(rem_usec - adj);

        /* Jump to 1ms diff, then increase fast (x2): EVERY loop
         * takes ~1 sec, people won't like slowly converging code here!
         */
    //bb_error_msg("adj:%d tv.tv_usec:%d", adj, (int)tv.tv_usec);
        if (adj < 512)
            adj = 512;
        /* ... and if last "overshoot" does not look insanely big,
         * just use it as adj increment. This makes convergence faster.
         */
        if (tv.tv_usec < adj * 8) {
            adj += tv.tv_usec;
            continue;
        }
        adj *= 2;
    }
    /* Debug aid to find "optimal" TWEAK_USEC with nearly exact sync.
     * Look for a value which makes tv_usec close to 999999 or 0.
     * For 2.20GHz Intel Core 2: optimal TWEAK_USEC ~= 200
     */
    //bb_error_msg("tv.tv_usec:%d", (int)tv.tv_usec);
#endif

    tm_time.tm_isdst = 0;
    xioctl(rtc, RTC_SET_TIME, &tm_time);

    if (ENABLE_FEATURE_CLEAN_UP)
        close(rtc);
}

#define HWCLOCK_OPT_LOCALTIME   0x01
#define HWCLOCK_OPT_UTC         0x02
#define HWCLOCK_OPT_SHOW        0x04
#define HWCLOCK_OPT_HCTOSYS     0x08
#define HWCLOCK_OPT_SYSTOHC     0x10
#define HWCLOCK_OPT_RTCFILE     0x20

int hwclock_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int hwclock_main(int argc UNUSED_PARAM, char **argv)
{
    const char *rtcname = NULL;
    unsigned opt;
    int utc;

#if ENABLE_FEATURE_HWCLOCK_LONG_OPTIONS
    static const char hwclock_longopts[] ALIGN1 =
        "localtime\0" No_argument "l"
        "utc\0"       No_argument "u"
        "show\0"      No_argument "r"
        "hctosys\0"   No_argument "s"
        "systohc\0"   No_argument "w"
        "file\0"      Required_argument "f"
        ;
    applet_long_options = hwclock_longopts;
#endif
    opt_complementary = "r--ws:w--rs:s--wr:l--u:u--l";
    opt = getopt32(argv, "lurswf:", &rtcname);

    /* If -u or -l wasn't given check if we are using utc */
    if (opt & (HWCLOCK_OPT_UTC | HWCLOCK_OPT_LOCALTIME))
        utc = (opt & HWCLOCK_OPT_UTC);
    else
        utc = rtc_adjtime_is_utc();

    if (opt & HWCLOCK_OPT_HCTOSYS)
        to_sys_clock(&rtcname, utc);
    else if (opt & HWCLOCK_OPT_SYSTOHC)
        from_sys_clock(&rtcname, utc);
    else
        /* default HWCLOCK_OPT_SHOW */
        show_clock(&rtcname, utc);

    return 0;
}