Unrolling and Shifting for Reconfigurable Architectures

Loops are an important source of optimization. In this paper, we propose a new technique for optimizing loops that con-tain kernels mapped on a reconfigurable fabric. We assume theMolen machine organization and programming paradigm as our framework. The method we propose extends our pre-vious work on loop unrolling for reconfigurable architec-tures by combining unrolling with shifting to relocate the function calls contained in the loop body such that in every iteration of the transformed loop, software functions (run-ning on GPP) execute in parallel with multiple instances of the kernel (running on FPGA). The algorithm is based on profiling information about the kernel’s execution times on GPP and FPGA, memory transfers and area utilization. In the experimental part, we apply this method to a loop nest extracted from MPEG2 encoder containing the DCT kernel. The achieved speedup is 19.65x over software execution and 1.8x over loop unrolling. 1