DescriptionIn a hierarchical design, timing budget would need to be split up properly between macros and levels of hierarchy so that the synthesis effort can be carried out efficiently. It is essential to have a robust method to determine the AT/RAT assertions for macro inputs/outputs so that the optimization tasks are fairly distributed between macros and top-level design. Many existing methods often determine the assertions based on one macro instance and/or one path through the input/output pins with other limitations. This paper describes a spring model approach for this timing/power budget apportionment problem. With the spring model approach, path delays are modeled as springs, and timing/power requirements are modeled as the compression/expansion of springs. The desired AT/RAT assertions are then determined by solving a system of equations. The spring equation can be generalized to incorporate other types of constraints and thus can be used to handle other budgeting problems. The general framework can incorporate multiple constraints with multiple instances simultaneously.