busybox/util-linux/hwclock.c

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/* 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 tarball for details.
*/
#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)
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{
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;
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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);
}
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#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
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#define HWCLOCK_OPT_RTCFILE 0x20
int hwclock_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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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 =
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"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"
;
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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 */
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if (opt & (HWCLOCK_OPT_UTC | HWCLOCK_OPT_LOCALTIME))
utc = (opt & HWCLOCK_OPT_UTC);
else
utc = rtc_adjtime_is_utc();
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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;
}