diff options
Diffstat (limited to 'util-linux')
| -rw-r--r-- | util-linux/hwclock.c | 94 |
1 files changed, 70 insertions, 24 deletions
diff --git a/util-linux/hwclock.c b/util-linux/hwclock.c index 6dff57f..08e5bd7 100644 --- a/util-linux/hwclock.c +++ b/util-linux/hwclock.c @@ -27,27 +27,12 @@ static time_t read_rtc(int utc) fd = rtc_xopen(&rtcname, O_RDONLY); ret = rtc_read_time(fd, utc); - close(fd); + if (ENABLE_FEATURE_CLEAN_UP) + close(fd); return ret; } -static void write_rtc(time_t t, int utc) -{ - struct tm tm; - int rtc = rtc_xopen(&rtcname, O_WRONLY); - - if (utc) - gmtime_r(&t, &tm); - else - localtime_r(&t, &tm); - tm.tm_isdst = 0; - - xioctl(rtc, RTC_SET_TIME, &tm); - - close(rtc); -} - static void show_clock(int utc) { //struct tm *ptm; @@ -58,10 +43,10 @@ static void show_clock(int utc) //ptm = localtime(&t); /* Sets 'tzname[]' */ cp = ctime(&t); - if (cp[0]) - cp[strlen(cp) - 1] = '\0'; + strchrnul(cp, '\n')[0] = '\0'; - //printf("%s %.6f seconds %s\n", cp, 0.0, utc ? "" : (ptm->tm_isdst ? tzname[1] : tzname[0])); + //printf("%s 0.000000 seconds %s\n", cp, utc ? "" : (ptm->tm_isdst ? tzname[1] : tzname[0])); + /* 0.000000 stand for unimplemented difference between RTC and system clock */ printf("%s 0.000000 seconds\n", cp); } @@ -81,12 +66,73 @@ static void to_sys_clock(int utc) static void from_sys_clock(int utc) { +#define TWEAK_USEC 200 + struct tm tm; struct timeval tv; + unsigned adj = TWEAK_USEC; + int rtc = rtc_xopen(&rtcname, O_WRONLY); + + /* Try to catch the moment when whole second is close */ + while (1) { + unsigned rem_usec; + time_t t; + + gettimeofday(&tv, NULL); + + rem_usec = 1000000 - tv.tv_usec; + if (rem_usec < 1024) { + /* Less than 1ms to next second. Good enough */ + small_rem: + tv.tv_sec++; + } + + /* Prepare tm */ + t = tv.tv_sec; + if (utc) + gmtime_r(&t, &tm); /* may read /etc/xxx (it takes time) */ + else + localtime_r(&t, &tm); /* same */ + tm.tm_isdst = 0; + + /* gmtime/localtime took some time, re-get cur time */ + gettimeofday(&tv, NULL); + + if (tv.tv_sec < t /* may happen if rem_usec was < 1024 */ + || (tv.tv_sec == t && tv.tv_usec < 1024) + ) { + /* We are not too far into next second. Good. */ + break; + } + adj += 32; /* 2^(10-5) = 2^5 = 32 iterations max */ + if (adj >= 1024) { + /* Give up trying to sync */ + break; + } + + /* Try to sync up by sleeping */ + rem_usec = 1000000 - tv.tv_usec; + if (rem_usec < 1024) { + goto small_rem; /* already close, don't sleep */ + } + /* Need to sleep. + * Note that small adj on slow processors can make us + * to always overshoot tv.tv_usec < 1024 check on next + * iteration. That's why adj is increased on each iteration. + * This also allows it to be reused as a loop limiter. + */ + usleep(rem_usec - adj); + } + + xioctl(rtc, RTC_SET_TIME, &tm); + + /* Debug aid to find "good" TWEAK_USEC. + * Look for a value which makes tv_usec close to 999999 or 0. + * for 2.20GHz Intel Core 2: TWEAK_USEC ~= 200 + */ + //bb_error_msg("tv.tv_usec:%d adj:%d", (int)tv.tv_usec, adj); - gettimeofday(&tv, NULL); - //if (gettimeofday(&tv, NULL)) - // bb_perror_msg_and_die("gettimeofday() failed"); - write_rtc(tv.tv_sec, utc); + if (ENABLE_FEATURE_CLEAN_UP) + close(rtc); } #define HWCLOCK_OPT_LOCALTIME 0x01 |