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Combining High Level Synthesis and Floorplan Together EDA Lab, Tsinghua University Jinian Bian
Outlines • Background • Combining High Level Synthesis and Floorplan together • The evolution of Combing HLS and Floorplan • The Basic Structure of Combining HLS and Floorplan • Conclusion and our future work
Background • The progress of manufactory technique for silicon chips has been slowed down under traditional design methodology • High performance / Low cost / Low power should be achieved by a more refined design, which means we need more powerful EDA tools
Background • The traditional EDA methodology has been challenged • The interconnect takes up most of resources: including area resource, delay resource, and power resource, etc. • The traditional design flow may cause a long design time, low design quality, even design failure under nanometer design environment • High performance / Low cost / Low power should be achieved by a more refined design, which means we need more powerful EDA tools
Traditional Design Flow High Level Synthesis HLS Optimize OK? N Y Floorplan FP Optimize OK? N Y Chip Optimize OK? N
Problems • High Level Synthesis and Floorplan are based on different Optimization Model • No Interconnect Information in High Level Synthesis • No Behavior Information in Floorplan • May cause a long design time, low design quality, even design failure
High Level Synthesis Fast Floorplan Meet Constraints? HLS & Fast FP Optimized OK? Final Floorplan Chip Optimized OK? Forgoing Optimized Flow Y Y N Y N Y Y N
Forgoing optimized Flow • High level synthesis using floorplan to get some physical information; • Re-synthesis after floorplanning to optimize the design. But, • Long loop time； • The estimation of Interconnect Information may far from final Chip； • Floorplan is passive.
Optimized Design Flow • Interconnect Information can be got through a fast floorplan tool • The estimation of Interconnect Information may far from final Chip
Proposed New Design Flow Controller Q/A High Level Synthesis Floorplan The Chip
Proposed Design Flow • High Level Synthesis and Floorplan can communicate with each other • The functionality of High Level Synthesis and Floorplan are both enhanced • The result of allocation and scheduling can be restructured by Floorplan • The Information of Interconnect can be retrieved easily • The optimization of HLS and FP are based on a same estimation model • Evolutional synthesis and floorplanning, to guarantee quicker astringency
Target Design Flow • The main loop from High Level Synthesis and Floorplan can be avoid • The optimizations of High Level Synthesis and Floorplan are consistent • Can achieve a shorter running time of tools and a better quality of circuits
To Achieve the “Target Design Flow” • High Level Synthesis Oriented Physical Information Estimation • Floorplan Aware High Level Synthesis • Behavior Aware Floorplan • High Level Synthesis and Floorplan Oriented Parameterized Functional Unit Library
1. High Level Synthesis Oriented Physical Information Estimation • HLS oriented high level physical information model and estimation technology • Physical Information Estimation oriented fast floorplan and placement
1.1 HLS oriented physical information model and estimation technology of a module • To create HLS oriented physical information model，through studying the existing information of physical design and IP core • To study the relationship of logic struction vs. physical information (interconnect, power, conjestive, etc.) before phsical design
1.2 quick floorplanning technique to estimate physical information • To get physical information with different accurate • Techniques: • Partitioning and clustering • Quick floorplanning algorithm • Placement information in a module
2. Floorplan Aware High Level Synthesis • Floorplan aware High Level Synthesis • Pre-partition before floorplan • Interconnect aware HLS • Analysis and Information retrieval of the result of Floorplan • Constraints generation for Floorplan • Incremental High Level Synthesis after Floorplan
Floorplan Aware High Level Synthesis • Constraints from HLS to floorplan • boundary constraints, • adjacent constraints, • separation constraints, • delay constraints of each net, • alternative modules for each functional unit, • area constraints, • etc. • Constraints from floorplan to HLS • delay constraints for each functional unit, • area constraints for each functional unit, • etc.
Floorplan Constraints Generation High Level Physical Information Estimation Floorplan FeedBack: HLS Constraints Generation Scheduling and Allocation Delay Constraint In HLS Adjacent Constraint In Floorplan Allocation Constraint In HLS
2.1. HLS techniques combined with floorplanning • HLS algorithm considering physical info. of every module and the interconnect information between modules • Get information from a module library with functionality and performance parameters and justify the design result • Technology mapping and functional unit assignment
2.2 floorplanning constraint generation after HLS • To transfer the information, requests and constraints of HLS to floorplanning • E.g. group information, adjacent relationship, critical paths, etc.
2.3 Re-synthesis after floorplanning • Adjust functional unit assignment and binding without florplan result to enhance the performance . • Adjust schedule result to change the timing constraint • To enhance the layout result.
3. Behavior Aware Floorplan • Behavior aware Floorplan • Partition and Clustor based on behavior information • Floorplan under uncertain data • Floorplan can change the result of allocation from HLS • Incremental Floorplan after High Level Resynthesis
3.1. Constraints and behavior driven floorplanning • To satisfy the circuit functionality and timing constaints • Behavior constraints are as a guidance for floorplanning
3.2. floorplanning technique with incomplete information • including： • Undetermined module shapes or areas • Undetermined pins， • Undetermined module numbers • Possible solutions • Soft-module floorplanning techniques • Shape-alterable polygons • Unit and module mixed • Etc.
3.3. Incremental floorplanning after synthesis • To keep the basic structure and to keep the parameter unchanged.
4. HLS and Floorplan Oriented Parameterized FU Library • Functional Unit Interface for both High Level Synthesis and Floorplan • Provide prototype and instance of each functional unit • Fast Estimation of physical information for un-stored functional unit
Conclusion and future work • The main frame of Combining High Level Synthesis and Floorplan • The structure of the parameterized functional unit library
Conclusion and future work • Floorplan aware High Level Synthesis • Floorplan under uncertain conditions • Constraints and feedback generation and transfer between High Level Synthesis and Floorplan