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script PLC subroutine bug


kmonroe023
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I've noticed what I think is a bug with the way subroutines handle local (L) variables.

 

I have a simple PLC that calls 2 subprograms, the first toggles the return value "bSecToggle" from 0 to 1 at the rate designated by the first variable passed. In the example below the output variable toggles at a rate of one second. Calling this subroutine is conditioned upon variable "foo1".

 

The second subroutine simply accumulates a timer as long as the passed variable is non-zero.

 

I've noticed that if both subroutines are called, neither functions as expected. If I set "foo1" equal to 0 to disable calling the first subroutine, the second performs as expected. Likewise if I disable the second subroutine the first functions as expected. It appears that the local variables of one subroutine are stepping on the other.

 

Is this the desired behavior? I assumed that local variables inside sub-programs were unique to each sub-program. However, my tests indicate otherwise.

 

Please see my code below:

 

open plc 1

// one second toggle timer
if (foo1 == 1){
call toggleTimer(1,&bSecToggle);
}

// Cycle Timer logic

call mainCycleTimer(bCutterRunning,&cycleTime);

close

 

Here is the subroutine code (both subprogs are in the same .pmc file):

open subprog mainCycleTimer (CutterRunning,&timerOut)

local CycleTimeStarted,CycleTimeStart;

if(CutterRunning==1 && CycleTimeStarted!=1)
{
CycleTimeStart=Sys.Time;
CycleTimeStarted=1;
}

if (CutterRunning==1)
{
timerOut=Sys.Time - CycleTimeStart;
} else {CycleTimeStarted=0}


return;
close

open subprog toggleTimer (tTime,&outFlag)

local ToggleTimer,ToggleTimeStart;

// Toggle timer logic
if (ToggleTimeStart==0){
ToggleTimeStart=Sys.Time;
}
else{
ToggleTimer=Sys.Time-ToggleTimeStart
}

if (ToggleTimer>tTime){
ToggleTimeStart=0;
ToggleTimer=0;

if (outFlag==0){
	outFlag = 1;
}
	else {outFlag=0}
}

return;
close

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Each top level program in Power PMAC (each PLC program, each coordinate system for a motion program) has its own stack of local variables. But for a given top-level program, it is the same stack when different subroutines are called. This explains the behavior you are seeing.

 

It is good general practice -- and needed in your case -- not to expect that subroutines can retain a value from one call to the next in a local variable.

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