Method of target generation for multilevel hierarchical circuit designs

• US 5,475,607 A
• Filed: 04/12/1994
• Issued: 12/12/1995
• Est. Priority Date: 04/12/1994
• Status: Expired due to Term

• Current Assignee: GlobalFoundries, Inc.
• Original Assignee: International Business Machines Corporation
• Inventors: Gupta, Rajesh, Apte, Jitendra
• Primary Examiner(s): Trans, Vincent N.
• Application Number:
  US08/226,603
• Time in Patent Office: 609 Days
• Field of Search: 364/488, 364/489, 364/490, 364/491, 364/578
• US Class Current: 716/113
• CPC Class Codes: G06F 30/30 Circuit design
• CPC Class Codes: G06F 30/392 Floor-planning or layout, e.g. partitioning or placement

Abstract

Generating delay targets for creating a multilevel hierarchical circuit design by providing a hierarchical design description and delay constraints of the circuit design; generating a net measure for each net and macro cell of the circuit design, and generating an abstract delay model for each macro cell of the circuit design based on the design description, wherein net measure is the estimated resistive-capacitive delay of a net derived from the estimated length of the net based on area-driven design, and an abstract delay model is a description of delays through a macro cell; generating delay targets for the nets and macro cells based on the net measures, the abstract delay models and the delay constraints; and creating the circuit design based on the delay targets.

Claims

1. A method of generating delay targets for creating a multilevel hierarchical circuit design, comprising the steps of:

(a) providing a hierarchical design description and delay constraints of the multilevel hierarchical circuit design, wherein the hierarchical design description describes the interrelationship between cells, including macro cells, input/output ports, and nets in the mutilevel hierarchical design;

(b) generating a net measure for each net and macro cell of the multilevel hierarchical circuit design and generating an abstract delay model for each macro cell of the multilevel hierarchical circuit design based on the hierarchical design description, wherein net measure is the estimated resistive-capacitive delay of a net derived from the estimated length of the net based on area-driven design, and an abstract delay model is a description of delays through a macro cell;

(c) generating delay targets for the nets and macro cells based on net measures, the abstract delay models and the delay constraints; and

(d) creating the multilevel hierarchical circuit design based on said delay targets.

2. A method according to claim 1, wherein step (b) comprises the steps of:

(e) determining the net measure of each net in the multilevel hierarchical circuit design;

(f) determining delay of the longest delay path, if any, from the input port to the output port for each paired input/output port of each macro cell in the multilevel hierarchical circuit design;

(g) determining the net measure of each said longest delay path; and

(h) determining delay and net measure for each input and output port of each macro cell;

wherein the abstract delay model for each macro cell comprises the delays determined for the macro cell in steps (f) and (h).

3. A method according to claim 2, wherein, if a net has a known path, then step (e) comprises using estimated resistive-capacitive delay for said known path for determining net measure of the net.

4. A method according to claim 2, wherein, if a net does not have a known path, but the net has end-points that are fixed, then step (e) comprises using estimated resistive-capacitive delay based on a Steiner tree topology for said known path for determining net measure of the net.

5. A method according to claim 2, wherein, if a net does not have a known path, and the net has end-points that are not fixed, but the net has a specified net measure, then step (e) comprises accessing the specified net measure for the net and using the specified net measure.

6. A method according to claim 2, wherein, if a net does not have a known path, and the net has end-points that are not fixed in location, and the net does not have a specified net measure, then step (e) comprises determining an estimated average connection length for the net and determining net measure for each source/sink pair of the net using estimated resistive-capacitance delay for said estimated average connection length for determining net measure of the net.

7. A method according to claim 2, wherein step (h) comprises the steps of:

determining delay of the longest delay path, if any, from each input port to a latch within the macro cell, and delay of the longest delay path to each output port from a latch within the macro cell; and

determining net measure of each said longest path delay.

8. A method according to claim 1, wherein step (c) comprises the steps of:

(i) setting an arrival time and a required arrival time for each port of each latch cell child and each port of each macro cell child of each macro cell that has a path to or from a latch within the macro cell;

(j) determining path slack and path weight for each port and each child cell of each macro cell that has a required arrival time specified therefor;

(k) determining path slack and path weight for each net and each child cell of each macro cell;

(l) determining a delay target for each net and each macro cell child of each macro cell; and

(m) determining timing constraints for each macro cell child of each macro cell.

9. A method according to claim 8, wherein step (i) comprises setting an arrival time and a required arrival time for each macro cell child based on clocking scheme and delay constraints of the multilevel hierarchical circuit design.

10. A method according to claim 8, wherein step (j) comprises the steps of:

(n) setting arrival times and path weights for each net and each child cell of each macro cell based on arrival time and path weight of the nets feeding each child cell and the child cells feeding each net, wherein the path weight of a net or child cell is the sum of its net measure and the maximum path weight among the child cells or nets feeding it; and

(o) determining path slack of each net that has a required arrival time specified therefor as the difference between its required arrival time and arrival time.

11. A method according to claim 8, wherein step (k) comprises determining path slack and path weight for each net and child cell based on the path slack and path weight of the child cells and nets fed by the net, wherein the path slack of a net is the minimum path slack among the child cells fed by the net, and wherein the path weight of a net is the maximum path weight among the child cells fed by the net, and wherein the path slack of a child cell is the minimum path slack among the nets fed by the child cell, and wherein the path weight of a child cell is the maximum path weight among the nets fed by the child cell.

12. A method according to claim 8, wherein the timing constraints at step (m) comprise arrival times and required arrival times for the macro cells generated based on static timing analysis.