Pixhawk原生固件PX4之日期时间的确定
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偶然注意到PX4日志中老是出现类似于2000.01.01 00:00:00这种日期(有兴趣的可以搜索一下千年虫问题)，于是结合代码进行了一波分析。
最后定位到gmtime_r(FAR const time_t *timer, FAR struct tm *result)这个函数以及struct tm这个结构体。
/*
* time.h
* /
...
struct tm
{
int tm_sec; /* second (0-61, allows for leap seconds) */
int tm_min; /* minute (0-59) */
int tm_hour; /* hour (0-23) */
int tm_mday; /* day of the month (1-31) */
int tm_mon; /* month (0-11) */
int tm_year; /* years since 1900 */
int tm_wday; /* day of the week (0-6) */ /*not supported by NuttX*/
int tm_yday; /* day of the year (0-365) */ /*not supported by NuttX*/
int tm_isdst; /* non-0 if daylight savings time is in effect */ /*not supported by NuttX*/
};PX4中所有输出的函数都是由tm这个结构体给出的。
这里需要注意到的是tm_year是从1900.01.01 00:00:00年开始计的。称为系统时间System Time。
而gmtime_r()是根据从1970.01.01 00:00:00后的秒数换算过来的。称为格林威治时间/Unix time。
这实在是一件有意思的事情啊。
下面给出gmtime_r()函数的换算过程吧，有趣
/****************************************************************************
* libc/time/lib_gmtimer.c
*
* Function: gmtime_r
*
* Description:
* Time conversion (based on the POSIX API)
*
****************************************************************************/
FAR struct tm *gmtime_r(FAR const time_t *timer, FAR struct tm *result)
{
time_t epoch;
time_t jdn;
int year;
int month;
int day;
int hour;
int min;
int sec;
/* Get the seconds since the EPOCH */
/* 纪元开始 1970.01.01 00:00:00*/
epoch = *timer;
sdbg("timer=%d\n", (int)epoch);
/* Convert to days, hours, minutes, and seconds since the EPOCH */
jdn = epoch / SEC_PER_DAY; // 天数
epoch -= SEC_PER_DAY * jdn; // 减去 天数 * 一天的秒数
hour = epoch / SEC_PER_HOUR; // 小时数
epoch -= SEC_PER_HOUR * hour; // 减去 小时数 * 一小时的秒数
min = epoch / SEC_PER_MIN; // 分钟数
epoch -= SEC_PER_MIN * min; // 减去 分钟数 * 一分钟的秒数
sec = epoch; // 最终秒数
sdbg("hour=%d min=%d sec=%d\n",
(int)hour, (int)min, (int)sec);
/* Convert the days since the EPOCH to calendar day */
clock_utc2calendar(jdn, &year, &month, &day); // 确定日期，自1970.1.1之后的
sdbg("jdn=%d year=%d month=%d day=%d\n",
(int)jdn, (int)year, (int)month, (int)day);
/* Then return the struct tm contents */
result->tm_year = (int)year - 1900; /* Relative to 1900 */
result->tm_mon = (int)month - 1; /* zero-based */
result->tm_mday = (int)day; /* one-based */
result->tm_hour = (int)hour;
result->tm_min = (int)min;
result->tm_sec = (int)sec;
return result;
}上面调用了clock_utc2calendar函数，将UTC确定的天数转换成年月日。
#ifdef CONFIG_GREGORIAN_TIME // 公历时间
/* Only handles dates since Jan 1, 1970 */
/* 处理1970.1.1之后的日期 */
static void clock_utc2calendar(time_t days, int *year, int *month, int *day)
{
int value;
int min;
int max;
int tmp;
bool leapyear;
/* There is one leap year every four years, so we can get close with the
* following:
*/
value = days / (4*365 + 1); /* Number of 4-years periods since the epoch 多少个四年 */
days -= value * (4*365 + 1); /* Remaining days 剩余天数 */
value <<= 2; /* Years since the epoch 左移两位，乘以4，得到从EPOCH后的年数 */
/* Then we will brute force the next 0-3 years */
// 简单匹配接下来的0到3年
// 将剩下的天数分配到接下来的3年
for (;;)
{
/* Is this year a leap year (we'll need this later too) */
leapyear = clock_isleapyear(value + 1970);
/* Get the number of days in the year */
tmp = (leapyear ? 366 : 365);
/* Do we have that many days? */
if (days >= tmp)
{
/* Yes.. bump up the year */
value++;
days -= tmp;
}
else
{
/* Nope... then go handle months */
break;
}
}
/* At this point, value has the year and days has number days into this year */
*year = 1970 + value;
/* Handle the month (zero based) */
min = 0;
max = 11;
do
{
/* Get the midpoint */
value = (min + max) >> 1; // value = (min + max)/2
/* Get the number of days that occurred before the beginning of the month
* following the midpoint.
*/
tmp = clock_daysbeforemonth(value + 1, leapyear); // (value + 1)月开始前过了多少天了
/* Does the number of days before this month that equal or exceed the
* number of days we have remaining?
*/
if (tmp > days)
{
/* Yes.. then the month we want is somewhere from 'min' and to the
* midpoint, 'value'. Could it be the midpoint?
*/
tmp = clock_daysbeforemonth(value, leapyear);
if (tmp > days)
{
/* No... The one we want is somewhere between min and value-1 */
max = value - 1;
}
else
{
/* Yes.. 'value' contains the month that we want */
break;
}
}
else
{
/* No... The one we want is somwhere between value+1 and max */
min = value + 1;
}
/* If we break out of the loop because min == max, then we want value
* to be equal to min == max.
*/
value = min;
}
while (min < max);
/* The selected month number is in value. Subtract the number of days in the
* selected month
*/
days -= clock_daysbeforemonth(value, leapyear);
/* At this point, value has the month into this year (zero based) and days has
* number of days into this month (zero based)
*/
*month = value + 1; /* 1-based */
*day = days + 1; /* 1-based */
}
#endif /* CONFIG_GREGORIAN_TIME */然后返回到gmtime_r()函数可以确定，struct tm结构体的赋值源头所在。
闲人看来是历史遗留问题，懒得改了。
最后的结论是，在使用tm的结构体时，要把年数加1900，月数加1，才能得到正确的UTC时间。
关于北京东八区的问题这里不再论述，之前在log日志正确显示的博文中已经有介绍，笔者觉得结合这篇博客看才是真。
然后回到2000.01.01这个日期上来，没有接收GPS的授时信息的情况下，默认时间会是它。而不是1970.01.01！显然这30年的差距得有代码站出来认了。
关于这个，系统默认时间。
一个猜测是CLOCK_REALTIME与CLOCK_ACTIVETIME两个clk_id的选取
/* CLOCK_REALTIME refers to the standard time source. For most implementations,
* the standard time source is the system timer interrupt. However, if the
* platform supports an RTC, then the standard time source will be the RTC
* for the clock_gettime() and clock_settime() interfaces (the system timer
* is still the time source for all of the interfaces).
*/
#define CLOCK_REALTIME 0
/* If an RTC is supported, then the non-standard CLOCK_ACTIVETIME is also
* supported to manage time based on the system timer interrupt separately from
* the RTC. This may be necessary, for example, in certain cases where the
* system timer interrupt has been stopped in low power modes.
*
* CLOCK_ACTIVETIME is only recognized by clock_gettime() and clock_settime().
*/
#ifdef CONFIG_RTC
# define CLOCK_ACTIVETIME 1
#else
# define CLOCK_ACTIVETIME CLOCK_REALTIME
#endif因为系统在确定当前时间时调用了这个函数
/*
* sdlog2.c
*/
bool get_log_time_tt(struct tm *tt, bool boot_time) {
struct timespec ts;
px4_clock_gettime(CLOCK_REALTIME, &ts); // 请注意，时间由我定
/* use RTC time for log file naming, e.g. /fs/microsd/2014-01-19/19_37_52.px4log */
time_t utc_time_sec = 0;
if (_gpstime_only && has_gps_3d_fix) {
utc_time_sec = gps_time_sec;
} else {
utc_time_sec = ts.tv_sec + (ts.tv_nsec / 1e9);
}
if (utc_time_sec > PX4_EPOCH_SECS) {
/* strip the time elapsed since boot */
if (boot_time) {
utc_time_sec -= hrt_absolute_time() / 1e6;
}
/* apply utc offset (min, not hour) */
utc_time_sec += _utc_offset*60;
struct tm *ttp = gmtime_r(&utc_time_sec, tt);
return (ttp != NULL);
} else {
return false;
}
}
px4_clock_gettime()的时间由clk_id决定，最后链接到clock_gettime()
/*
* px4_time.h
*/
#elif defined(__PX4_LINUX) || defined(__PX4_NUTTX) || defined(__PX4_DARWIN)
#define px4_clock_gettime clock_gettime
#define px4_clock_settime clock_settime
这里提一点：目前还是没有能够找到一个合适的编辑器查看PX4代码，时常会跳转错误。特别是涉及到NuttX后，非常多相同名称的函数，针对posix、qurt、NuttX的，还望细心。
/************************************************************************
* Name: clock_gettime
*
* Description:
* Clock Functions based on POSIX APIs
*
************************************************************************/
int clock_gettime(clockid_t clock_id, struct timespec *tp)
{
#ifdef CONFIG_SYSTEM_TIME64
uint64_t msecs;
uint64_t secs;
uint64_t nsecs;
#else
uint32_t msecs;
uint32_t secs;
uint32_t nsecs;
#endif
int ret = OK;
sdbg("clock_id=%d\n", clock_id);
DEBUGASSERT(tp != NULL);
/* CLOCK_REALTIME - POSIX demands this to be present. This is the wall
* time clock.
*/
#ifdef CONFIG_RTC
if (clock_id == CLOCK_REALTIME || clock_id == CLOCK_ACTIVETIME)
#else
if (clock_id == CLOCK_REALTIME)
#endif
{
/* Do we have a high-resolution RTC that can provie us with the time? */
#ifdef CONFIG_RTC_HIRES
if (g_rtc_enabled && clock_id != CLOCK_ACTIVETIME)
{
/* Yes.. Get the hi-resolution time from the RTC */
/////////// 使用RTC //////
ret = up_rtc_gettime(tp);
}
else
#endif
{
/* Get the elapsed time since power up (in milliseconds) biased
* as appropriate.
*/
/* 获取从系统上电后的时间 不上电不走数 */
msecs = MSEC_PER_TICK * (g_system_timer - g_tickbias);
sdbg("msecs = %d g_tickbias=%d\n",
(int)msecs, (int)g_tickbias);
/* Get the elapsed time in seconds and nanoseconds. */
secs = msecs / MSEC_PER_SEC;
nsecs = (msecs - (secs * MSEC_PER_SEC)) * NSEC_PER_MSEC;
sdbg("secs = %d + %d nsecs = %d + %d\n",
(int)msecs, (int)g_basetime.tv_sec,
(int)nsecs, (int)g_basetime.tv_nsec);
/* Add the base time to this. */
secs += (uint32_t)g_basetime.tv_sec;
nsecs += (uint32_t)g_basetime.tv_nsec;
/* Handle carry to seconds. */
if (nsecs > NSEC_PER_SEC)
{
uint32_t dwCarrySecs = nsecs / NSEC_PER_SEC;
secs += dwCarrySecs;
nsecs -= (dwCarrySecs * NSEC_PER_SEC);
}
/* And return the result to the caller. */
tp->tv_sec = (time_t)secs;
tp->tv_nsec = (long)nsecs;
}
sdbg("Returning tp=(%d,%d)\n", (int)tp->tv_sec, (int)tp->tv_nsec);
}
else
{
sdbg("Returning ERROR\n");
errno = EINVAL;
ret = ERROR;
}
return ret;
}
其中RTC的几个宏定义如下
/*
* rtc.h
*/
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/* Configuration ************************************************************/
/* CONFIG_RTC - Enables general support for a hardware RTC. Specific
* architectures may require other specific settings.
*
* CONFIG_RTC_DATETIME - There are two general types of RTC: (1) A simple
* battery backed counter that keeps the time when power is down, and (2)
* A full date / time RTC the provides the date and time information, often
* in BCD format. If CONFIG_RTC_DATETIME is selected, it specifies this
* second kind of RTC. In this case, the RTC is used to "seed" the normal
* NuttX timer and the NuttX system timer provides for higher resoution
* time.
*
* CONFIG_RTC_HIRES - If CONFIG_RTC_DATETIME not selected, then the simple,
* battery backed counter is used. There are two different implementations
* of such simple counters based on the time resolution of the counter:
* The typical RTC keeps time to resolution of 1 second, usually
* supporting a 32-bit time_t value. In this case, the RTC is used to
* "seed" the normal NuttX timer and the NuttX timer provides for higher
* resoution time.
*
* If CONFIG_RTC_HIRES is enabled in the NuttX configuration, then the
* RTC provides higher resolution time and completely replaces the system
* timer for purpose of date and time.
*
* CONFIG_RTC_FREQUENCY - If CONFIG_RTC_HIRES is defined, then the frequency
* of the high resolution RTC must be provided. If CONFIG_RTC_HIRES is
* not defined, CONFIG_RTC_FREQUENCY is assumed to be one.
*
* CONFIG_RTC_ALARM - Enable if the RTC hardware supports setting of an
* alarm. A callback function will be executed when the alarm goes off
*/有CONFIG_RTC_HIRES的说明可以看出，定义了此项后，有飞控板上的纽扣电池支持断电情况下的计时器工作，并且精度也是高高的。
那么问题来了。
经过实际测试，编写时间获取程序，发现，时间是在系统上电时才增加。
int fantasy_test_main(int argc, char *argv[])
{
PX4_INFO("Hello Sky!");
time_t timeSec = time(NULL);//1970.01.01
struct tm tt;
struct tm *timeinfo = gmtime_r(&timeSec, &tt);
PX4_INFO("The time is %d-%d-%d %d:%d:%d \n",\
timeinfo->tm_year+1900,\
timeinfo->tm_mon+1,\
timeinfo->tm_mday,\
timeinfo->tm_hour,\
timeinfo->tm_min,\
timeinfo->tm_sec);
return 0;
}时间一直是从2000.01.01 00：00：00开始的，并且只有USB上电时间才增加，难道电池没电?
而GPS给出的UTC秒数，由下列代码可以看出
#
# vehicle_gps_position.msg
#
uint64 time_utc_usec # Timestamp (microseconds, UTC), this is the timestamp which comes from the gps module. It might be unavailable right after cold start, indicated by a value of 0 最后的总结，确定当前系统时间时，先获取已经经过的秒数，再调用struct tm *timeinfo = gmtime_r(&timeSec, &tt);就能获取tm的时间了。
先接受一次GPS卫星授时吧，需要3d fix。
关于RTC时间，再看。
By Fantasy