touble with a time calculation

[EarlyBird2]

     if EL2_Enable = 1 THEN     ;  EL2 = EL1 current values - set overrun value  

       EL2_100th   = EL1_100TH   - Event1_OT_100th+100
        if EL2_100th<100 then 
          EL1_Seconds=EL1_Seconds-1
       Else
         EL2_100th=EL2_100th-100
      endif

    EL2_Seconds = EL1_Seconds - Event1_OT_sec+60
      if EL2_Seconds<60 then 
        EL1_Minutes=EL1_Minutes-1
     else
       EL2_Seconds =EL2_Seconds -60
     endif

       EL2_Minutes = EL1_Minutes - Event1_OT_Min +60
     if EL2_Minutes<60 then
       EL1_Hours=EL1_Hours-1
     else
       EL2_Minutes =EL2_Minutes -60
     endif

       EL2_Hours   = EL1_Hours   - Event1_OT_hour+24
     if EL2_Hours<24 then
        EL1_Days=EL1_Days-1
     else
       EL2_Hours   =EL2_Hours   -24
     endif

  EL2_Days    = EL1_Days    - Event1_OT_Day  
       
endif

Just something to try

[richard]

steve has the right idea for the math but since el1/el2 vars can be updated via the isr at any time during the calcs the results will vary.

statisticly it will fail about 4-5 times per hundred calcs based on :-
I think chances of failure are 1/60+1/60+1/100+1/24 I might be wrong about the stats

[EarlyBird2]

If isr affects EL1 vars create Temp_EL1 vars at the start of the routine and use these for the calculation.

[richard]

won't work . the isr can change the values as u copy them to the temp vars ,been there done that

[EarlyBird2]

Ok some problems do not have an answer.

Bye

[richard]

only solution I know is to disable isr and copy vars to a buffer then enable isr and then perform calcs on the buffered data.
it may mean the odd lost interrupt / whats worse incorrect calcs or missed ints
only the designer can make that call .