JPH03220749A - Layout design of standard cells - Google Patents

Abstract

PURPOSE:To arrange an external terminal and an internal cell associated with it close to each other to make the wiring between them shorter by giving a special connection strength to the net between the external terminal and the internal cell. CONSTITUTION:In layout design, special connection strength information is given to a net between an external terminal and an internal cell to be connected with the external terminal. This method includes, for example, a step 2 of giving a stronger connection strength to a net between cells in a lower hierarchy than to a net in a higher hierarchy, and another step 3 of giving a special connection strength to a net between an external terminal and an internal cell associated with the terminal. When a hierarchical net list 1 is given, the net is divided to discriminate between one connected with the external terminal and the other. The net connected with the external terminal is given strength information 4 in the step 3, while the other net is given strength information 4 in the step 2. If the information given in the step 3 is maximum, for example, the external terminal and its corresponding cell are preferentially laid close to each other, i.e., they are connected through shorter wiring.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a standard cell placement design method, and particularly to a standard placement method in which cells are placed preferentially in close proximity in descending order of connection strength.

[Conventional technology]

Conventionally, this type of standard cell placement method has been used to provide connection strength, and the netlist placement method has been used to provide connection strength by combining the netlist and logic design information (logical operation,
Connection strength was given based on logical attributes and signal line flow. In addition, the inventor of the present invention has proposed, as a standard cell placement method, that a net between cells in a lower hierarchy is given a stronger connection strength than a net between cells in an upper hierarchy. For example, see Japanese Patent Application No. 63-237001.

FIG. 2 is a flowchart illustrating the standard cell placement method of the prior application. 1 is a hierarchically described netlist, 2
is the process of giving stronger connection strength to the connections between cells in the lower hierarchy than the connections between cells in the upper hierarchy, 4 is the connection strength information obtained in step 2, and 5 is the standard according to netlist 1 and connection strength information 4 This is a method of automatically arranging cells.

According to this method, when providing the connection strength, no logical design information is required, and the connection strength can be provided using only a hierarchically described netlist.

[Problem to be solved by the invention]

The conventional standard cell placement method described above requires logic design information in addition to the netlist when providing connection strength. Requires a program to analyze the information, ■ It takes time to analyze the logical information (CP
U time). In addition, in the inventor's previous application, the net at the highest level is given the weakest strength, so the strength of the net between the external terminal and the internal cell connected to that terminal is the weakest. However, there is a problem in that the external terminal and the internal cell connected to the terminal are not placed close to each other, resulting in a long wiring.

SUMMARY OF THE INVENTION An object of the present invention is to provide a standard cell layout design method that eliminates these drawbacks and allows external terminals and internal cells connected to the terminals to be placed close to each other.

[Means to solve the problem]

The configuration of the present invention is based on a netlist in which connections between cells are described hierarchically, and the nets between cells in a lower hierarchy are
In the standard cell placement design method, which gives stronger connection strength information than the nets between cells in the upper hierarchy and places cells preferentially adjacent to each other in order of the connection strength, external terminals in the netlist and their terminals are The external terminal and the internal cell connected to this external terminal are arranged close to each other by providing special connection strength information to the net with the internal cell to be connected and performing layout design. It is characterized by

In the present invention, the special connection strength information can also be information about the strongest connection.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a flowchart illustrating one embodiment of the present invention. In the figure, 1 is a hierarchically described netlist, 2
3 is the process of giving a stronger connection strength to the net between cells in the lower hierarchy than the net between cells in the upper hierarchy, and 3 is the process of giving special connection strength to the net between the external terminal and the internal cell connected to that terminal. Step 4 shows the connection strength information obtained in step 2.3, and 5 shows the step of automatically arranging standard cells according to the netlist 1 and the connection strength information 4.

First, when netlist 1 is given, this net is separated into nets connected to external terminals and other nets, and for nets connected to external terminals, other nets are Connection strength information 4 is given to the net in step 2. For example, if the strength given in step 3 is made the strongest, the external terminal and the five internal cells connected to that terminal will be placed in close proximity with the highest priority.

〔Effect of the invention〕

As explained above, the present invention provides special connection strength (for example, making it the strongest) to the net between an external terminal and an internal cell connected to that terminal. This has the effect that the internal cells are arranged close to each other and their wiring can be shortened.

[Brief explanation of drawings]

FIG. 1 is a flowchart for explaining one embodiment of the present invention, and FIG. 2 is a flowchart for explaining a conventional standard cell arrangement method. 1...Netlist described hierarchically, 2...Process of providing connection strength in consideration of the hierarchy, 3...Process of providing connection strength regarding external terminals, 4...Connection strength information as a result , 5... Automatic placement method.

Claims (1)

[Claims] 1. Based on a netlist in which connections between cells are described hierarchically, connection strength information is given to nets between cells in lower hierarchies that are stronger than nets between cells in upper hierarchies. , in the standard cell layout design method in which cells are placed preferentially in close proximity in order of connection strength, a special connection is made to a net between an external terminal in the netlist and an internal cell connected to that terminal. 1. A standard cell layout design method, characterized in that the external terminal and the internal cell connected to the external terminal are arranged close to each other by performing the layout design by giving strength information. 2. The standard cell layout design method according to claim 1, wherein the special connection strength information is information indicating the strongest connection.