docs: def addPort(n: LNode, intf: Interface):
      """
      Add LayoutExternalPort for interface
      """
      d = PortTypeFromDir(intf._direction)
      ext_p = LayoutExternalPort(
          n, name=intf._name, direction=d, node2lnode=n._node2lnode)
      ext_p.originObj = originObjOfPort(intf)
      n.children.append(ext_p)
      addPortToLNode(ext_p, intf, reverseDirection=True)
      return ext_p