It is important to note that the splitting of the NPU process into two parts, namely, the GNPU and the LNPU (that work in tandem), is a necessary condition for Lemma 6 to hold.
Caption: Figure 8: Layer-level view of the pipeline timing diagram for the GNPU and LNPU arrays when two NPU arrays are employed to process four layers.
Here, the GNPUs compute VN messages as per (4) and the LNPUs compute CN messages as per (5).