Computer-aided design and analysis of circuits and semiconductor – Nanotechnology related integrated circuit design
Reexamination Certificate
1998-05-05
2001-07-10
Smith, Matthew (Department: 2825)
Computer-aided design and analysis of circuits and semiconductor
Nanotechnology related integrated circuit design
C008S094240, C008S094240, C008S094240
Reexamination Certificate
active
06260179
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a technology for evaluating a wiring condition among cells disposed in a specified region, which is developed to decide arrangement of cells (circuit elements) for designing an integrated circuit such as an LSI or circuitry on a printed circuit board. More particularly, the invention relates to a method for predicting a wiring density among cells, a storage medium for storing a wiring density predicting program and a cell arranging device for arranging cells by using the wiring density predicting method.
2) Description of the Related Art
Generally, for designing an integrated circuit such as an LSI, first, logical designing is performed based on logical specifications which satisfy functions of an LSI to be designed. Then, packaging designing is performed based on a net list obtained by the logical designing. During packaging designing, cells (circuit elements) are arranged based on the net list and then wiring is performed among the cells.
A conventional interactive cell arranging system has used a procedure like that shown in
FIG. 16
for arranging cells while evaluating a wiring condition.
The specific procedure goes as follows. First, cells are properly disposed in a specified region based on a net list (step S
1
). Then, for evaluating a wiring condition among the cells disposed in the specified region, a certain wiring program is started to perform temporary wiring (global wiring or Manhattan wiring) among the cells (step S
2
). Then, based on the result of the temporary wiring, a wiring density among the cells is determined and a wiring condition is evaluated (step S
3
).
If the cell arrangement is determined to be O.K. as a result of evaluating the wiring condition (YES route from step S
4
), the process proceeds to an actual wiring operation (step S
6
). On the other hand, if the wiring condition is not good (NO route from step S
4
), the cells are rearranged (step S
5
). Then, the process returns to step S
2
and repeats the operations from step S
2
to step S
5
. In this way, the cells are arranged in a good wiring condition (i.e., a condition for enabling real wiring to be quickly performed) before a real wiring operation is performed.
However, there is a problem inherent in the foregoing conventional interactive cell arranging system. Specifically, as described above with reference to
FIG. 16
, for evaluating a wiring condition among the cells disposed in the specified region, temporary wiring is performed by running a wiring program for each of the results of arranging in step S
1
and step S
5
and a wiring density is then obtained. Consequently, a great deal of time is required for temporary wiring processing.
Generally, considerable time is needed for wiring processing among cells, even for such easily estimated wiring as Manhattan wiring or the like. Especially, as a circuit is larger in size, more time is needed. As a result, if a wiring program is run for each rearranging of cells, a great deal of time is required for realizing cell arrangement of a good wiring condition and even circuit designing efficiency is greatly reduced.
SUMMARY OF THE INVENTION
The present invention was made in order to solve the problem discussed above. It is an object of the present invention to provide a wiring density predicting method, a storage medium for storing a wiring density predicting program and a cell arranging device, whereby circuit designing efficiency can be increased by predicting a cell wiring density only based on a cell arranging result without starting any wiring programs and easily making wiring evaluation based on the wiring density within a short time.
In order to achieve the objective, according to the present invention, the wiring density predicting method for predicting a wiring density among a number of cells disposed in a specified region for designing a circuit comprises the steps of dividing the specified region into a plurality of evaluation unit grids, selecting two cells to be connected by wiring, obtaining a rectangular region in which the pins of the two cells to be connected are diagonal vertexes, calculating probability of wiring between the pins of the two cells to be connected passing through one grid point of wiring grids in the rectangular region as wiring line passing probability by assuming that probability of the wiring between the pins of the two cells to be connected passing through each grid point of the wiring grids is uniform in the rectangular region, calculating a proportion of the rectangular region occupying each evaluation unit grid as a rectangular region occupancy ratio, calculating a value obtained by multiplying the wiring passing probability by the rectangular region occupancy ratio for each evaluation unit grid as a first wiring density influence value to be used as an index for a wiring density increase made by the wiring in the evaluation unit grid and calculating, for each evaluation unit grid, a sum of first wiring density influence values calculated for all wiring lines among a number of cells as a wiring density in the evaluation unit grid.
In this case, if a wiring inhibited region exists in the specified region, the process may take the steps of calculating a proportion of the wiring inhibited region occupying each evaluation unit grid as a wiring inhibited region occupancy ratio, calculating, by assuming that probability of wiring existence is 1 in the wiring inhibited region, a value obtained by multiplying the probability 1 by the wiring inhibited region occupancy ratio for each evaluation unit grid as a second wiring density influence value to be used as an index for a wiring density increase made by the wiring inhibited region in the evaluation unit grid and calculating, for each evaluation unit grid, a value obtained by adding the second wiring density influence value to the sum of the first wiring density influence values as a wiring density in the evaluation unit grid.
The process may also take the steps of calculating a proportion of each cell occupying each evaluation unit grid as a cell occupancy ratio, the cell being disposed in the specified region, calculating, for each evaluation unit grid, a value obtained by multiplying the cell occupancy ratio by a wiring direction ratio in the cell, the wiring direction ratio being preset for the cell, as a third wiring density influence value to be used as an index for a wiring density increase made by the cell in the evaluation unit grid and calculating, for each evaluation unit grid, a value obtained by adding the third wiring density influence value to the sum of the first wiring density influence values as a wiring density in the evaluation unit grid.
For determining the positions of the pins of the two cells to be connected so as to obtain the rectangular region, representative pin information registered in a cell library regarding the pins of the cells to be connected may be used. In a normal mode, all bits of pin information registered in the cell library regarding the pins of the cells to be connected may be used. In a high-speed mode, only representative pin information registered in the cell library regarding the pins of the cells to be connected may be used.
For obtaining the rectangular region, a size of the rectangular region may be adjusted based on a bypassing rate of a wiring route. Alternatively, the first wiring density influence value may be weighted based on a wire width according to a wiring variety.
Furthermore, if cell arrangement is changed after a wiring density among a number of cells is predicted and a wiring density is to be predicted again based on the changed cell arrangement, the process may take the steps of subtracting the first and third wiring density influence values calculated for the cell to be changed in arrangement before the arrangement change from a wiring density in the evaluation unit grid of the cell, calculating, for each evaluation unit grid, first and third wiring density influence values for the cell after the arrangement c
Maruyama Terunobu
Ohsawa Keiko
Armstrong Westerman Hattori McLeland & Naughton LLP
Fujitsu Limited
Smith Matthew
Thomson A. M.
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