ROM to DSP block transfer for resource constrained synthesis
Modern field programmable gate array (FPGA) architectures are moving towards heterogeneity with the increasing inclusion of coarse grained elements such as embedded multipliers and RAMs. This has given rise to a multi-dimensioned resource-based measure of design area, very different from the traditional application-specific integrated circuit figure of silicon area. In order for a designer to use these heterogenous elements in their design, they must usually specifically instantiate them. Heterogeneous elements not used in a design remain unused on the device, consuming leakage power, silicon area and manufacturing costs. Method of transferring functionality normally implemented in embedded ROMs and 4-input look-up tables (4-LUTs) onto unused digital signal processor (DSP) blocks is proposed. The paper proceeds to include this method in a synthesis system incorporating the idea of resource constrained synthesis, where a design is mapped to an FPGA considering user and device constraints on heterogenous element usage, based on an extension to the Altera Quartus II synthesis software. Results have been obtained, showing an improvement over existing methods in 76% of the 21 ROMs examined. Further results have been obtained from applying this approach with the synthesis system to benchmark algorithms. In the designs examined, the number of possible implementations has increased by two to four times over Altera Quartus.
