The Real output y is a ramp signal with circular easing into and out of the ramp:
If parameter duration is set to 0.0, the limiting case of a Step signal is achieved.
If curvature is set to 0.0 then the exact behavior of Modelica.Blocks.Sources.Ramp is achieved.
If curvature is set to 1.0 then the there is circular easing into and out of the change in height with no linear ramp.