On multi-cycle path support in model based high-level synthesis

Multi-cycle paths (MCPs) are commonly used by designers as an efficient way to relax the timing constraints on eligible paths in their designs. MCP directs synthesis tools to relax the optimization on the specified paths. The MCP constraints are widely used in the Register Transfer Level (RTL) designs and are propagated to downstream tools. With the evolution of high level synthesis (HLS) tools, design entry and the constraints have to be specified at a higher level of abstraction. In addition, majority of the HLS users are system level designs or DSP experts who have little knowledge of RTL implementation flows. Hence, it is important for HLS tools to provide a methodology for specifying MCP constraints at a higher level of abstraction, consider the MCP paths during HLS and also forward annotate the MCP constraints to the RTL implementation tools. In this paper, we have created such a methodology for Synopsys Synphony model compiler (SMC), a model based HLS tool. To the best of our knowledge, MCP is supported for the first time in model based HLS flow. The effectiveness of specifying MCP on higher abstraction level is demonstrated on sample example designs.