class ASPDevice
{
...
        ~ASPDevice() { DemoMode(false); } //will wait for timer to exit clean
	Atomic demo; //0=disabled, 1=running demo mode, 2=a timer cb is executing
        bool isdemo;
        IsDemoMode() const { return isdemo; }
...
}

void ASPDevice::DemoMode(bool b)
{
	bool _b = isdemo;
	isdemo = b;
	if(!_b && isdemo) //start only one time, maybe here is a problem still, because not atomic
	{
		ASSERT(AtomicInc(demo)==1);
		SetTimeCallback(0, THISBACK(GenDemoData), 2);
	}
	else if(_b && !isdemo)
	{
		KillTimeCallback(2); //very important, timer might be not executin currently
		AtomicDec(demo);
		while(AtomicRead(demo) > 0) Sleep(1);
		ASSERT(AtomicRead(demo)==0);
	}
}

void ASPDevice::GenDemoData()
{
	ASSERT(AtomicInc(demo)==2);

...
//do your refresh stuff here, dont forget an AtomicDec(demo) on error exits
...
	
	int a = AtomicDec(demo);
	if(a<=0) return; //if has been desabled, dont restart
	ASSERT(a>=0);
	ASSERT(IsDemoMode());
	SetTimeCallback(200, THISBACK(GenDemoData), 2); //inkl a jitter
}