The subgraph bfCascadingChain creates a cascading chain of beamforming kernels. Review the graph definition in the src/inc/subsys.h. It is a templated subgraph with parameters xoff, yoff, and len. The xoff and yoff parameters define the coordinate of the leftmost AI Engine. The len parameter specifies the length of the cascading chain (len-2 = the number of middle kernels in a chain). The port arrays din[len] and cin[len] are the data input and coefficient input ports. Their sizes are determined by the len parameter (so you need one data input port and one coefficient input port for each kernel in the cascade chain). Additionally, there is one output port out, for the final output in the last kernel.
You can create subgraphs that contains multiple cascading chains. Each chain can be customized to contain any number of beamforming kernels.