Links for implementing calendar functions in the embedded system?

Question

I have a built-in system that currently tracks seconds until an event occurs, using a real-time clock controlled by the crystal of the clock.

Now he needs to keep track of the actual date and time. So I need to calculate the day, month, year, hour, minute and second from the start / time date and offset in seconds.

Can someone point me in the right direction to account for leap years, daylight saving time (DST) and other complications?

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Hardware solutions are not an option, as this feature is added to an existing product. The RTC peripheral is integrated into the MCU selected for the next generation device.

Answer 1

C fragment archive contains some functions of date and time . Update: unfortunately, the C snippets archive now does not work. I updated the link to point to the web archive of the page.

See also " Julian day ", Wikipedia , which includes formulas for Julian date calculation .

A " calculation of the Julian date " A Google search should reveal more if you want to continue the search.

Answer 2

I am bored, I could not resist trying to solve. Here's a prototype in ruby ​​- should be clear enough to translate to C.

offset , : Baseyear, Baseday, Basesec, 0 = 1,

#initialize outputs
year= Baseyear
day = Baseday
sec = Basesec+offset

#days & seconds remaining in the current year
is_leap = is_leap_year(year)
days_remaining = 365+(is_leap ? 1 : 0) - day
secs_remaining = SEC_PER_DAY*days_remaining

#advance by year
while (sec>=secs_remaining)
  sec-=secs_remaining
  year+=1
  is_leap = is_leap_year(year)
  days_remaining = 365+(is_leap ? 1 : 0)
  secs_remaining = SEC_PER_DAY*days_remaining
  day=0 
end

#sec holds seconds into the current year, split into days+seconds
day += sec / SEC_PER_DAY
day = day.to_i #cast to int
sec %= SEC_PER_DAY

#lookup month
for i in (0..11)
  dpm = DAYS_PER_MONTH[i] # =[31,28,31,30,...]
  if (i==1 && is_leap) 
   dpm+=1
  end
  if day < dpm
   month = i
   break
  else
    day-=dpm
  end
end

day+=1 #1-based
hour = sec/3600
min = (sec%3600)/60
sec = sec%60
puts "%s %d, %d @ %02d:%02d:%02d" % [MONTHNAME[month],day,year, hour, min, sec]

, DST .

Answer 3

- C, , ( - ), PJ Plauger "Standard C Library" .

Answer 4

, :

bool is_leap_year(int year)
{
    return ((0 == year % 400) || ((0 == year % 4) && (0 != year % 100)));
}