Question and Answers

•  What are the advantages and disadvantages of Control flow based CDFG over Data flow based CDFG?

Answer:

In data flow based CDFG, we can represent parallel evaluation by operational and storage nodes for all branches of a control node. This is in real sense more near to hardware realization of the circuit, compared to that of the control flow based CDFG, where only that set of operational and storage nodes are executed for which (branch) the value of control node is satisfied. Therefore, optimizations and other steps of HLS are more suitable to be performed on data flow based CDFG.

On the hand, data flow based CDFG is more tedious to draw from the specifications compared to the control flow based counterpart. In control flow based CDFG there is almost one-to-one mapping between the nodes of the CDFG and the lines of DHL code. If there are nested loops and conditions in the input specifications then it should be flattened before extracting the data flow based CDFG. Further, in such cases the CDFG may have a large number of nodes.