SCALP: an iterative-improvement-based low-power data path synthesis system

In this paper, we present SCALP, a comprehensive low-power data path synthesis system that performs the various high-level synthesis tasks (transformations, scheduling, clock selection, module selection, and hardware allocation and assignment) with an aim of reducing the power consumption in the synthesized data path. Focusing on only one or a small subset of the high-level synthesis tasks makes it difficult to realize the full potential for power savings at the algorithm and architecture levels. Our synthesis algorithms, which are based on an iterative improvement strategy with efficient pruning techniques, are capable of performing the various high-level synthesis tasks (and considering their interactions) in an efficient manner. Supply voltage and clock period pruning strategies are used for quickly eliminating inferior design points during the search for the minimum power solution. Estimating switched capacitance accurately at intermediate stages during high-level synthesis can be challenging since the exact structure of the circuit, which affects both physical capacitance and switching activity, may not be available, and due to the high computational complexity of running register-transfer level power analysis tools several times during high-level synthesis. SCALP overcomes the above problems by maintaining a complete image of the structural register-transfer level (RTL) circuit (this is possible since we have a complete solution at any point during iterative improvement), and employing a very fast switched capacitance estimation technique that Is based on the concept of switched capacitance matrices. Our system can handle diverse module libraries and utilize complex scheduling constructs such as multicycling, chaining, and structural pipelining. Retiming and functional pipelining are used in our system to meet tight performance constraints, and to enable the ensuing synthesis steps to better explore the implementation space. Results on several real-life examples are presented to demonstrate the effectiveness of the algorithm. Power estimates obtained using switch-level simulation after layout indicate that up to an order-of-magnitude of power savings can be obtained using our synthesis system.