JP3247011B2 - Cell placement improvement apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for improving cell layout in automatic layout of VLSI (Large Scale Integrated Circuit). With the recent development of circuit technology, VL
There are remarkable improvements in the degree of integration of SI and the increase in circuit scale.

As the degree of integration and circuit scale increase, V
The number of cells included in an LSI chip has also increased, and it has become increasingly difficult to obtain an optimal solution for cell placement.
For this reason, it is desired to improve the processing efficiency of calculating the optimal solution of the cell arrangement.

[0003]

2. Description of the Related Art Conventionally, after the initial placement of cells such as a VLSI is determined, the method of locally correcting the cell position and reducing the wiring length includes (1) cell rotation, (2) cell movement,
(3) The cells were exchanged, and the respective operations were performed as follows.

(1) The cell is rotated by 90 degrees to calculate the wiring length. If the wiring length is reduced by this rotation, the cell is placed in that direction. (2) Move the cell to a vacant place and calculate the wiring length. If the wire length is reduced by this movement, the cell is placed at that location.

(3) Two or more cells are selected and their positions are exchanged. The wiring lengths before and after the replacement are compared, and when the wiring length is shortened by the replacement, the position is determined as the position after the replacement, and otherwise the position is returned to the original position.

[0006]

The above-described conventional method of finding the position of a cell in which the wiring length is reduced has the following problems.

(1) When rotating a cell, it is necessary to calculate the wiring length for one cell in four directions at 90 degrees. (2) When a cell is moved, it is necessary to calculate the wiring length when the cell is moved to all places where the cell can be placed.

(3) When exchanging cells, when n cells are exchanged and when two cells are exchanged, it is necessary to check n-1 combinations of wiring lengths for one cell. Was.

According to the present invention, a region (hereinafter, referred to as "cell vector") is calculated for all cells after the initial placement is determined, in which, when the cell is moved to the location, the wiring length of the cell is unchanged or reduced. By rotating, moving, and exchanging cells in a cell vector, the number of candidates to be examined is reduced, and the processing efficiency is improved.

[0010]

SUMMARY OF THE INVENTION The present invention has the following construction to solve the above-mentioned problems. FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 1A is an explanatory diagram of a cell vector, and FIG. 1B is a device configuration diagram.

In FIG. 1A, the cell vector of the cell A is indicated by hatching. The center of the cell A is a point c and the center point of the movement of the cell A is c ', and the cell A is connected to the other cells b, d, and e by a net (wiring). In addition,
The number of the wiring is the length of the wiring.

In FIG. 1B, an input unit 12 is for inputting initial position data such as cell position information and connection relation between a cell and a net. The cell placement improving unit 11 calculates a cell vector and changes the rotation, movement, exchange, etc. of the cell to improve the cell placement. The output unit 13 outputs a cell position after the cell arrangement is improved, a connection relation between the cell and the net, a wiring length, and the like.

[0013]

The operation based on the above configuration will be described with reference to FIG. From the input unit 12 of FIG. 1B, the position information of each cell,
Initial placement data such as a connection relationship between a cell and a net is input to the cell placement improving unit 11.

The cell placement improving section 11 calculates, for all the cells, a region where the wiring length of the cell remains unchanged or decreases when the cell is moved, and defines the region as a cell vector.

Next, the cell placement improving unit 11 reduces the wiring length by changing the rotation, movement, replacement, etc. of the cell in the cell vector. In the example of FIG. 1A, when the center of cell A is at point c, the wiring length of cell A and cell b is 7, the wiring length of cell A and cell d is 7, and the wiring length of cell A and cell e. Is 9
And the total wiring length of the cell A is 23. When the center point c of the cell A is moved to the inner point c ′ of the cell vector A, the total wiring length is reduced to 19.

The cell position, the connection relationship between the cell and the net, the wiring length, and the like after the improvement by the cell arrangement improving unit 11 are output from the output unit 1.
3 is output. As described above, for each cell, a cell vector, which is a region where the wiring length is reduced, is calculated in advance, the number of candidates to be examined can be reduced, and the processing efficiency of local arrangement improvement can be improved.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. 2 to 10 are views showing an embodiment of the present invention.

§1: Description of Cell Vector A method for obtaining a cell vector which is an area where the wiring length of a certain cell is invariable or reduced when a certain cell is locally moved after the initial placement is determined.

For each cell, a section where the wiring length is unchanged or reduced in each of the X and Y directions is calculated, and the calculated section is used as a cell vector. This cell vector becomes a rectangular area including the center of the cell, and depends on the number and direction of nets coming out of the cell.

The calculation procedure in the X direction will be described below. (1) Let the x coordinate of the cell center be c _x . (2) A net is considered as a vector having a cell center c _x as a start point and a center of a connected cell as an end point.

(3) Sort the nets in ascending order of ascending X coordinate of the end point. The X coordinate of the net end point after sorting and x _1, x ₂ ···. (4) FIG. 2 is an explanatory diagram of a cell vector when the total number of nets is an even number (2n).

A. When c _x <x _n (see FIG. 2A),
At this time, the starting point c _x of the net, which is the cell center, is located on the left side (negative side) of the ending point x _n of half (2n) / 2 of the total number of nets, so that the wiring length decreases in the section between c _x and x _n. Then x
_In the section between _n and x _{n + 1} , the line length is in the middle, and when one increases, the other decreases by the same amount, so that the wiring length remains unchanged.

Section [c _x , x _n ]: Decrease ····· Section [x _n , x _{n + 1} ]: Invariant ···· When x _n <c _x <x _{n + 1} (refer to FIG. 2B), at this time, the wiring length is invariable because the starting point c _x of the net is located at an intermediate position of the number of ending points of the net.

Section [x _n , x _{n + 1} ]: invariant When x _{n + 1} <c _x (see FIG. 2C), at this time, the starting point c _x of the net is on the right side (upper side) of the intermediate position of the total number of nets (the position of the above item B). long, with x _n and x _{n + 1} of intervals unchanged, it will be reduced in a section of x n _{+ 1} and c _x.

Interval [x _n , x _{n + 1} ]: invariant ··· · Interval [x _{n + 1} , c _x ]: decreasing ····· min (c _x , shows a x _n) to take whichever c _x and x _n small _{addition, max (c x, x n} + 1) to c _x and x _{n + 1,} whichever is larger to take each If the above sections ( ₁ ) to (4) are put together, the area in the X direction of the cell vector is [min (c _x , x _n ), m
ax (c _x , x _{n + 1} )].

[0026] In the case the total number of calculations net Y direction even (2n), like the X-direction, a region of the Y-direction is _{[min (c y, y n)} , max (c y, y n ₊₁ )]. (5) FIG. 3 shows that the total number of nets is odd (2n + 1)
FIG. 4 is an explanatory diagram of a cell vector in the case of FIG.

A. When c _x = x _{n + 1} (see FIG. 3A), at this time, the starting point c _x of the net coincides with x _{n + 1 in} the middle of the end point of the net, so that the wiring length is unchanged or reduced. There are no sections.

B. When c _x <x _{n + 1} (see FIG. 3 (b)), since the start point c _x of the net is on the left side (negative side) of the middle x _{n + 1 of the} end point of the net, c _x and x _{n The} wiring length decreases in the section of ₊₁ .

Section [c _x , x _{n + 1} ]: Decrease C. When x _{n + 1} <c _x (see FIG. 3C), at this time, the start point c _x of the net is on the right side (upper side) of the middle x _{n + 1 of the} end point of the net, so x _{n + 1} and c _The wiring length decreases in the section of _x .

[Interval (x _{n + 1} , c _x ): Decrease] Therefore, from the above interval, the area of the cell vector in the X direction is [min (c _x , x _{n + 1} ), max (C _x ,
_{xn + 1} )]. Similarly, the Y-direction of the region of Serubekuta _{[min (c y, y n +} 1), max (c y, y
_{n + 1} )].

§2: Description of Rotating Cells After the initial placement of cells, cell vectors are calculated for all cells, and if the cells are rotated by 90 degrees, it is checked whether the wiring length is reduced. The cells are arranged in a direction in which the wiring length becomes shorter. If the cell goes out of the cell vector area during this rotation, the direction is excluded from the candidates without calculating the wiring length, and the next direction is examined.

FIG. 4 is an explanatory view of the case where the cell is rotated. When the direction of the wiring coming out of the cell A is fixed, when the cell A is rotated by 180 degrees, the wiring length of the cell A and the cell b is short. Here is an example.

§3: Description of the case where cells are moved After the initial placement of cells, cell vectors are calculated for all cells. Next, one movable position of the cell is detected in the cell vector, and the cell is moved. As a result, the cell arrangement is changed, so that the cell vector is recalculated for the moved cell and the cell connected to the cell by the net.

FIG. 1 shows the case where the center point c of the cell A is moved to c ′. The case where the total wiring length is reduced from 23 to 19 by moving the center point from c to c ′ is shown. Show.

It is effective to check the moving location of the cell A from the end of the cell vector where the wiring length is likely to decrease. After this movement, the rotation described with reference to FIG. 4 is further performed to reduce the wiring length of the cell.

§4: Description of Cell Exchange After the initial placement of cells, cell vectors are calculated for all cells. Next, a pair of replaceable cells is detected and replaced. The exchangeable cells can be exchanged in pairs of cells each having its own cell center in the cell vector area of the other party.

Since the exchange changes the cell vectors of the exchanged cells and the cells connected by their nets, the corresponding cell vectors are recalculated. This is repeated until there are no more replaceable pairs.

FIG. 5 is an explanatory diagram for exchanging two cells. FIG. 5A shows exchangeable cells A and B.
In this case, the cell center of cell A is in the cell vector of cell B, and the cell center of cell B is in the cell vector of cell A.

Before the replacement, the wiring length of the cell A is 9 for the cell A and the cell d, 7 for the cell A and the cell f, 7 for the cell A and the cell h, and the wiring length of the cell B is 23 B and cell e are 3 and cell B and cell g are 10, which is 13 in total.

The wiring length of the cell A after the replacement is 5 for the cell A and the cell d, 3 for the cell A and the cell f, 11 for the cell A and the cell h, and the wiring length of the cell B is 19 B and cell e are 7, and cell B and cell g are 6, giving a total of 13.

FIG. 5B shows the wiring length before and after the replacement of the cells A and B. After the replacement, the entire wiring length is reduced. FIG. 6 is a processing flowchart for exchanging two cells. Hereinafter, description will be given according to the processing numbers S1 to S5.

S1: Two cells (c
1, c2) is determined. Two overlapping cells c1,
If c2 exists (YES), the process proceeds to the process number S2. if,
If there are no two overlapping cells c1 and c2 (NO), this process ends (STOP).

S2: It is determined whether the cell c2 is included in the cell vector of the cell c1. If the cell c2 is included in the cell vector of the cell c1 (YES), the process moves to the process number S3. If the cell c2 is not included in the cell vector of the cell c1 (NO), the process returns to the processing number S1, and the next candidate is checked with the processing number S1.

S3: It is determined whether the cell c1 is included in the cell vector of the cell c2. When the cell c1 is included in the cell vector of the cell c2 (YES), the process proceeds to a process number S4. If the cell c1 is not included in the cell vector of the cell c2 (NO), the process returns to the processing number S1, and the next candidate is examined.

S4: The two cells c1 and c2 are exchanged, and the process proceeds to the processing number S5. S5: Recalculate the cell vectors of the exchanged cells c1 and c2 and the cells connected to them by a net, and return to the processing number S1.

The exchange of the two cells in FIG. 6 is as follows.
It is effective to perform the operation from a long distance, where the wiring length is likely to decrease. After the processing of FIG. 6, the wiring length of each cell is calculated.

Further, after the replacement of the cells, the rotation of the cells described with reference to FIG. 4 can be performed to reduce the wiring length. §5: Description of exchanging three cells After the initial arrangement of cells, cell vectors are calculated for all cells. Next, the exchangeable cell triplet is detected,
Exchange. With this replacement, the wiring length does not change or decreases. Since the exchange changes the cell vectors of the exchanged cells and the cells connected by those nets, the cell vector of the corresponding cell is recalculated. This exchange is repeated until there are no more exchangeable triplets.

FIG. 7 is an explanatory diagram 1 for exchanging three cells. FIG. 7A shows exchangeable cells A, B, and C.
Is shown. In FIG. 7A, the numbers are the wiring lengths. In this case, the cell center of cell B is included in the cell vector of cell A,
The cell center of the cell C is included in the cell vector of the cell B, and the cell center of the cell A is included in the cell vector of the cell C.

Thus, by replacing the cell A in the position of the cell B, replacing the cell B in the position of the cell C, and replacing the cell C in the position of the cell A in the counterclockwise direction, the wiring length is unchanged or reduced. Become.

Before this replacement, the wiring length of cell A is
Cell A and cell d are 12, cell A and cell g are 10, cell A
And the cell k becomes 10, which is 32 in total. The wiring length of cell B is 10 for cell B and cell e, and 10 for cell B and cell f.
And a total of 20. The wiring length of the cell C is
The cell C and the cell h are 8, the cell C and the cell i are 12, the cell C and the cell j are 12, and the total is 32.

After this replacement, the wiring length of the cell A becomes
Cell A and cell d are 4, cell A and cell g are 10, cell A and cell k are 10, and the total is 24. The wiring length of cell B is 16 for cell B and cell e, and 4 for cell B and cell f, for a total of 20. The wiring length of the cell C is 14 for the cell C and the cell h, 6 for the cell C and the cell i, and 6 for the cell C and the cell j, for a total of 26.

FIG. 7B shows the wiring lengths before and after the replacement of the cells A, B, and C.
The overall wiring length has decreased. FIG. 8 is an explanatory diagram 2 for exchanging three cells, and FIG. 8 (A) is an explanation of clockwise cell exchange.

In FIG. 8A, the cell center of cell B is included in the cell vector of cell A, the cell center of cell C is included in the cell vector of cell B, and the cell center of cell A is included in the cell vector of cell C. Have been.

In this case, by changing the positions of the cells in the clockwise direction such as cell A → cell B, cell B → cell C, cell C → cell A, the wiring length is unchanged or reduced.

FIG. 8B is an explanation of the cell list.
The list L1 of the cell c1 is a list of other cells existing in the cell vector area of the cell c1. In this example, the cell c2, cell c12, cell c
4 are held. The list L2 of the cell c1 is the cell c1
9 is a list of other cells when the position of 1 exists in another cell vector. In this example, the list L2 of the cell c1
Holds a cell c16 and a cell c3.

Similarly, the cell c9 and the cell c3 are included in the list L1 of the cell c2, and the cell c9 is included in the list L2 of the cell c2.
1. Cell c8 is held. in this way,
By holding two types of lists for each cell, FIG.
In (B), a triple of cell c1, cell c2, and cell c3 can be detected.

FIG. 9 is a flowchart of a process for exchanging three cells. Hereinafter, the process numbers S11 to S17 in FIG.
It will be described according to. S11: Two cells (c1, c2) with overlapping cell vectors
Determine if there is. When there are two overlapping cells c1 and c2 (YES), the process proceeds to the process number S12. If overlapping 2
If there are no two cells c1 and c2 (NO), this process ends (STOP).

S12: It is determined whether the cell c2 is included in the cell vector of the cell c1. If the cell c2 is included in the cell vector of the cell c1 (YES), the process proceeds to a process number S14.
If the cell c2 is not included in the cell vector of the cell c1 (NO), the process proceeds to a process number S13.

S13: It is determined whether the cell c1 is included in the cell vector of the cell c2. When the cell c1 is included in the cell vector of the cell c2 (YES), the process proceeds to a process number S14.
If the cell c1 is not included in the cell vector of the cell c2 (NO), the process returns to the process number S11 to check the next candidate.

S14: It is determined whether or not there is a cell c3 in which the cell c3 is included in the cell vector of the cell c2 and the cell c1 is included in the cell vector of the cell c3. Such a cell c3
If there is (YES), the process proceeds to the process number S16. If there is no such cell c3 (NO), the process number S1
Move to 5.

S15: It is determined whether or not there is a cell c3 in which the cell c3 is included in the cell vector of the cell c1 and the cell c2 is included in the cell vector of the cell c3. Such a cell c3
If there is (YES), the process proceeds to the process number S16. If there is no such cell c3 (NO), the processing number S1
Return to 1 and examine the next candidate.

S16: The three cells c1, c2, and c3 are exchanged, and the process proceeds to processing number S17. S17: Recalculate the cell vectors of the exchanged cells and the cells connected to them by the net, and execute the process number S11.
Return to

As described above, after the three cells have been exchanged, the wiring length can be reduced by further rotating the cells described with reference to FIG. §6: Description of Combination of Three-Cell and Two-Cell Replacement When reducing the wiring length by combining three-cell replacement and two-cell replacement, first, replace three replaceable cells. An exchange is performed, and then two exchangeable cells are exchanged.

FIG. 10 is a flowchart of a process for exchanging three cells and two cells. Hereinafter, the processing number S2
A description will be given according to 1 to S26. S21: Like the process numbers S11 to S15 in FIG.
It is determined whether there is a set of replaceable cells. If there is a replaceable cell triplet (YES), the process proceeds to the process number S22.
If there is no replaceable cell triplet (NO), the process proceeds to the process number S24.

S22: The exchangeable three cells are exchanged, and the process proceeds to processing number S23. S23: Recalculate the cell vectors of the exchanged cells and the cells connected to the exchanged cells by the net, and execute the process number S21.
Return to

S24: It is determined whether or not there are two replaceable cells as in the case of the process numbers S1 to S3 in FIG. When there are two replaceable cells (YES), processing number S25
Move on to If there is no replaceable cell pair, this process is terminated (STOP).

S25: The exchangeable two cells are exchanged, and the process proceeds to the processing number S26. S26: Recalculate the cell vectors of the exchanged cells and the cells connected to the exchanged cells via the net, and process number S24
Return to

After the exchange of the three cells and the exchange of the two cells, the wiring length can be reduced by further rotating the cells described with reference to FIG.

[0069]

As described above, according to the present invention, the cell length is calculated by calculating the cell vectors for all the cells after the initial arrangement of the cells and rotating, moving, exchanging the cells in the cell vectors. Can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is an explanatory diagram of a cell vector when the total number of nets is an even number (2n) in the embodiment.

FIG. 3 shows an example in which the total number of nets is an odd number (2n +
It is explanatory drawing of the cell vector in case of 1).

FIG. 4 is an explanatory diagram when a cell is rotated in the embodiment.

FIG. 5 is an explanatory diagram for exchanging two cells in the embodiment.

FIG. 6 is a processing flowchart for exchanging two cells in the embodiment.

FIG. 7 is an explanatory diagram 1 for exchanging three cells in the embodiment.
It is.

FIG. 8 is an explanatory diagram 2 for exchanging three cells in the embodiment.
It is.

FIG. 9 is a processing flowchart for exchanging three cells in the embodiment.

FIG. 10 is a processing flowchart for exchanging three cells and two cells in the embodiment.

[Explanation of symbols]

 A, b, d, e cell c center point c of cell A center point of cell A after movement 11 cell placement improving unit 12 input unit 13 output unit

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-64-32385 (JP, A) JP-A-4-94556 (JP, A) JP-A-2-119242 (JP, A) JP-A-6-32 332983 (JP, A) JP-A-6-259504 (JP, A) JP-A-5-63087 (JP, A) JP-A-5-61846 (JP, A) JP-A-4-360555 (JP, A) JP-A-4-27976 (JP, A) JP-A-4-252050 (JP, A) JP-A-3-108358 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G06F 17/50 H01L 21/82

Claims (2)

(57) [Claims] An input means (12) for inputting initial placement data of a cell to a cell placement improving means (11) ;
Calculating means for calculating a region in which the sum of the wiring lengths is invariable or shorter than before the movement; and cell arrangement improving means (11) for changing the rotation, movement, exchange, etc. of the cells in the region. Characteristic cell placement improvement device. 2. After the initial placement of a cell, for each cell, when the cell is moved to that location, all connected to that cell
Calculating an area in which the sum of the wiring lengths of the wirings is unchanged or shorter than before the movement , and changing the cells in the area.