Going with the Flow: Bridging the Gap between Theory and Practice in Physical Design

摘要

A practical Physical Design flow is an intricate chain of many algorithms. Assorted placers andrnrouters are interspersed with incremental logical synthesis algorithms that patch up timing. Thernoverall goal is to address a plethora of design objectives simultaneously such as LVS/DRCrncorrectness, speed, area, power and yield. Each new technology node adds additional complicationsrnto flow. Increased crosstalk sensitivity, and tighter power and yield requirements are currentlyrncausing havoc in 28nm.rnEDA research has been focused primarily on improving individual algorithms. Over the pastrndecade ISPD has hosted contests to find the best placement and global routing tool. Thoughrnimportant, does it really matter for each algorithm to be optimal? And what does ‘optimal’ meanrngiven the many conflicting objectives? This presentation focuses on the overall flow issues basedrnon the experiences with a state-of-the-art commercial physical design toolset.rnIt is important to be up-front about priorities in a multi-objective design flow. Which effectsrndominate and which can be addressed incrementally? It is surprisingly hard to get good results fromrnan algorithm that uses conflicting objectives in its cost function. Instead, it is often preferable to letrneach algorithm address only a single issue and patch up the less important ones incrementally in thernnext steps. This presentation also addresses the ‘bumpiness’ of multi-algorithm flows. The manyrnlocal optima and limited experimental evidence make it hard to properly tune the chain ofrnalgorithms.