Making Fast Buffer Insertion Even Faster Via Approximation Techniques

As technology scales to 0.13 micron and below, designs are requiring buffers to be inserted on interconnects of even moderate length for both critical paths and fixing electrical violations. Consequently, buffer insertion is needed on tens of thousands of nets during physical synthesis optimization. Even the fast implementation of van Ginneken's algorithm requires several hours to perform this task. This work seeks to speed up the van Ginneken style algorithms by an order of magnitude while achieving similar results. To this end, we present three approximation techniques in order to speed up the algorithm: (1) aggressive pre-buffer slack pruning, (2) squeeze pruning, and (3) library lookup. Experimental results from industrial designs show that using these techniques together yields solutions in 9 to 25 times faster than van Ginneken style algorithms, while only sacrificing less than 3% delay penalty.