Patent Application: US-74420807-A

Abstract:
as circuit sizes have increased , designs have become increasingly hierarchical . it is common for designs to have large numbers of macro blocks ; many of these blocks are “ soft ,” and may have variable width and height . the present invention provides an alternate method to handle designs with large numbers of blocks . rather than approaching them as expanded floorplanning , the problems are re - cast as traditional mixed size placement , and many macro blocks are treated as standard cells . using existing mixed size placement tools , the superior reported are obtained . first , an effective “ standard block design ” methodology is provided . second , new mixed size placement legalization algorithms that are more robust than the widely - used mixed - size tetris algorithm is presented .

Description:
in accordance with a first embodiment of the invention , “ hb ” [ 8 ] placements were first converted to “ standard block ” formulations , using the method described . the number of soft and hard blocks in the “ original ” version , and the number of “ cells ” and “ blocks ” in the conversion according to the present invention , are shown in the first few columns of table 1 . table 1 : wire length comparisons of the “ standard block ” approach according to the present invention , using the mixed size placement tools feng shui 5 . 1 , with the legalizer according to the present invention , and capo 9 . 5 . capo 9 . 5 , converts floorplanning problems into mixed size placement problems in which all soft blocks are square ; these results are shown in the third wire length column . the methods of patoma and the floorplanner parquet 2 are compared . for two designs , hb06 and hb15 , the automatic conversion provided by capo 9 . 5 resulted in overlapping ( non - legal ) placements . table 1 also lists the total percentage of area that can be considered single - height “ cells ” in the formulation according to the present invention ; note that these are in fact macro blocks , and the cell abstraction is used to enable the use of mixed - size placement tools . even when a block cannot be adjusted to be a single row in height , it may be possible to adjust it so that it is an integral number of rows tall ; in many designs , there are large areas with no wasted space , with macro blocks aligning nicely in multi - row horizontal stripes . two widely - available mixed size placement tools , feng shui 5 . 1 and capo 9 . 5 , are used on the converted benchmarks , and half perimeter wire lengths are reported . in almost all cases , the patoma placement tool , explicitly developed for the “ hb ” benchmarks , was outperformed by the earlier methods . from these results , it appears that the fact that many blocks are “ soft ” does not provide an advantage for patoma ; if a reasonable standard block height is selected , existing methods are more than adequate . as was noted , the default legalization method of feng shui performed poorly ; in almost all cases , the placements were illegal due to stacking . thus , only the abstract placement of feng shui is used , and then legalization performed using the methods describe herein . while performing these experiments , it was noted that capo 9 . 5 handled the original floorplanning problems in an unexpected way . it was anticipated that capo 9 . 5 would perform floorplanning , using the parquet floorplanner that had been integrated into the tool . instead , it appears that the floorplanning problems are converted into mixed size placement , but with all macro blocks being “ square .” in markov [ 12 ], the authors suggest that packing square blocks is the easiest option ; however , the results herein disagree , and the experimental results show that the present standard block methodology is more effective . capo 9 . 5 performs better with converted standard block files in accordance with the present invention , than with the simple “ square ” conversion performed natively , and is able to find legal placements for all benchmarks . in fig4 , placements for the benchmark hb01 are shown , using the standard block approach according to the present invention , with both feng shui and capo , the result of patoma , and the result when capo automatically converts the problem to contain square blocks . the methodology according to the present invention handles large designs well ; for small designs , traditional floorplanning methods are still appropriate . when using many soft blocks , a good “ row height ” is selected . when designing hard macro blocks , a design team should consider the shapes of other objects to be placed in the same chip , and plan accordingly . rather than allowing an explosion in the number of block sizes and shapes , it is quite beneficial to enforce consistent block heights ( or integer multiples thereof ) across a design . fixing the height of macro blocks also allows the development of a library of blocks that can be interchanged more easily . there is further advantage is a pre - selected height , in that it will allow predetermined locations of the pins for global signal nets , improving the routing quality of designs that employ the blocks . the impact of good height selection is clear ; the default choice made by capo 9 . 5 for square blocks results in a significant wire length overhead , and a failure to legalize placements in some instances . the tool with the greatest degree of freedom , the parquet floorplanner , produces by far the worst results . mixed size placement tools have already demonstrated great scalability [ 14 ], handling millions of cells easily ; 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