MEL PICBASIC Forum - A REALLY accurate clock.

  • A REALLY accurate clock.

    by
    Charles Linquis
    Published on - 26th September 2011 04:29
    Need to know the time - accurately for your next project?

    The code below allows your PIC to log into a network timeserver and it (eventually) writes the time to a Dallas RTC (code not supplied).
    The PIC checks the NET TIME every power-up and thereafter every 4 hours. If it doesn't make connection, it tries an alternate time server. If THAT doesn't work (after retries) it gives up and tries again 4 hours later. A Lantronix XPort handles the connection to the net.

    The PIC normally reads the time from the Dallas RTC. The clock is self-setting and self-correcting, as long as you have a network connection.

    And all of you using 16F chips, time to upgrade! This sub requires LONGS.


    Net Time' is the number of seconds since Jan 1 1900

    This sub accomodates for leap years, GMT offsets and Daylight Savings Time.

    The sub assumes you are in the present century, so it takes a shortcut by pre-subtracting the number of seconds from Jan 1 1900 to
    Jan 1 2009.

    It should be self-explanatory.


    Code:
    Hoffset is the hours offset from GMT
Sign = "1" or "2" depending on whether you are earlier or later than GMT
DST = 1 if you are in Daylight Savings Time  (Another part of the PGM changes that value when appropriate).


GETNETTIME:
       NETRETRYCOUNT = 0
              
GETNETTIME2:
      
       HSEROUT [13,10,"TIMESERVER ",#TSIP1,".",#TSIP2,".",#TSIP3,".",#TSIP4,13,10]
       PAUSE 100
     
        THEADER[0] = $2           ' STX
        THEADER[1] = TSIP1  ' DESTINATION IP
        THEADER[2] = TSIP2
        THEADER[3] = TSIP3
        THEADER[4] = TSIP4

        THEADER[5] = 0            ; DESTINATION PORT HIGHBYTE
        THEADER[6] = 123          ; DESTINATION PORT LOWBYTE
                    
        LRC1 = 0
        LRC2 = 0 
      
        For X = 1 to 6
             LRC1 = LRC1 ^ THeader[x]
        next X
                       
        THEADER[7] = LRC1               
        THEADER[8] = 0               
        THEADER[9] = 48                                             'Data Length lowbyte
    
;Send the header
          HSEROUT [13,10]     
          For X = 0 to 9
            HSEROUT2 [THeader[X]]
          Next X   
         
          LRC2 = LRC2 ^ THeader[8]
          LRC2 = LRC2 ^ THeader[9]
        
;Send the data
          HSEROUT2 [$1B]
           LRC2 = LRC2 ^ $1B
          For X = 0 To 46
            HSEROUT2 [0]
            LRC2 = LRC2 ^ 0
          NEXT X     
                  
;Send the Checksum (LRC)            
         
          HSEROUT2 [LRC2]
getresponse:         
         HSERIN2 1000,NoResponse,[Wait($2)]                                                      
         hserin2 200,NoResponse,[SKIP 41,TimeNow.Byte3,TimeNow.Byte2,TimeNow.Byte1,TimeNow.Byte0]
  
          READ 851,HOFFSET
               
               IF sign = "1" then
                  if DST = 1 and HOffset = 0 THEN 
                       Sign = "2"
                       GOTO OtherSide
                  ENDIF     
                    
                     TimeNow = Timenow - ((HOffset - DST) * 3600)
               ENDIF
             
OtherSide:             
               IF Sign = "2" THEN
               
                  TimeNow = TimeNow + ((Hoffset + DST) * 3600)
               ENDIF   
                                     
                SINCEJAN2009 = TIMENOW - 3439756800   ; 3439756800 is the #of sec from Jan1 1900 to Jan1 2009
               
                RUNNINGSECONDS = SINCEjAN2009
                YR = 2009
                
GETYEAR:
        
                    LEAP = (YR//4)    ; = 0 if leap year
                    
                    if LEAP = 0 then
                        SecondsInYear = 31622400 ;366*60*60**24
                     
                    ELSE
                        SecondsInYear = 31536000 ;365*60*60*24
                     
                    endif
                       
                    If RunningSeconds > SecondsInYear Then
                        RunningSeconds = RunningSeconds - SecondsInyear
                        YR = YR + 1
                        GOTO GetYear
                    ENDIF
               
                 Mo = 1 ; Start with Month = 1  
                        
        
GETMONTH:        
                IF LEAP > 0 THEN
                   lookup2 MO,[0,2678400,2419200,2678400,2592000,2678400,2592000,2678400,2678400,2592000,2678400,2592000,2678400],SecondsInMonth
                ELSE
                   LOOKUP2 MO,[0,2678400,2505600,2678400,2592000,2678400,2592000,2678400,2678400,2592000,2678400,2592000,2678400],SecondsInMonth
                ENDIF
                
                If RunningSeconds >= SecondsInMonth THEN
                   RunningSeconds = RunningSeconds - SecondsInMonth
                
                MO = MO + 1
                GOTO GETMONTH
                ENDIF   
FINDDAYS:
        
                DA = RUNNINGSECONDS/86400
                RUNNINGSECONDS = RUNNINGSECONDS//86400
     
                HR = RUNNINGSECONDS/3600 
                RUNNINGSECONDS = RUNNINGSECONDS//3600
       
                MN = RUNNINGSECONDS/60
                RUNNINGSECONDS = RUNNINGSECONDS//60
                SC = RUNNINGSECONDS
            
                Da = Da + 1
               HSEROUT [13,10,13,10,DEC2 HR,":",DEC2 MN,":",DEC2 SC,"   ",DEC2 MO,"/",DEC2 DA,"/",#YR,13,10] 

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    This article was originally published in forum thread: A REALLY accurate clock. started by Charles Linquis View original post