1. A system-on-chip apparatus, the apparatus comprising: a scan path comprising a first layer having a plurality of components, and a second layer having at least one component, wherein the second layer is adapted for being dynamically selected and deselected; wherein propagation of data within the first layer is controlled using at least one control signal; wherein propagation of data within the second layer is controlled using the at least one control signal and a layer selection control signal from the first layer, wherein the layer selection control signal is adapted for controlling propagation of data within the second layer independent of propagation of data within the first layer.