class Waveform(ReadonlyRegisterBase, ReadonlyRegisterArray):
    def doRead(self):
        time.sleep(0.001)
        #self.val = to_array(self.calc(), 'd')
        return self.calc()

    def getSize(self):
        return len(self.take(-1))    #only reads if cache is None

class SinusoidWaveform(Waveform):
    def calc(self):
        ret = []
        x = random.random()
        for i in range (20):
            ret.append(math.sin(x))
            x = x + 0.1
        return ret        

add_device(SinusoidWaveform("wf1"), True)

r3 = lscan(out, (wf1,),  0.0,1.0, 4, 0.01)