DLL on Metatrader 4 doesn't update with incoming ticks - dll

Question

I have written a simple DLL as part of a custom indicator for Metatrader 4, which is called thus:
int start( ) {
double Rates[][6];
int MaximumRecords = ArrayCopyRates( Rates, Symbol(), 0 );
for( int zz = MaximumRecords; zz >= 0; zz-- ) {
OutPut[zz] = EMPTY;
}
GetSMAArray( Rates, MaximumRecords, Periods, OutPut );
return(0);
}
This works fine in that it plots as expected on the chart, but unfortunately it does not update with new, incoming ticks - it just plots on its initial call. What further code can I add to make the DLL update with incoming ticks? Almost all my searches have come up with variations on the use of
ExtCountedBars = IndicatorCounted();
to force a while loop to calculate, but these all apply to calculations contained in the .mq4 file itself. I want to force the DLL to recalculate. Secondly, I would like this recalculation to occur only on the completion of a bar and not on the arrival of all and every tick.

Answer 1

For the on new bar only thing, I technique is to keep last bar's (Bars[0]) date time information in a variable, and if it has changed, this means a new bar has come.
datetime lastBarDateTime;
int start(){
if(Time[0]==lastBarDateTime)
return(0);
lastBarDateTime = Time[0];
// codes to run on a new bar ...
}
For DLL part, I actually couldn't have understood where you are using DLL in that code.