Method of estimating path delays in an IC

• US 7,082,587 B2
• Filed: 12/18/2002
• Issued: 07/25/2006
• Est. Priority Date: 12/18/2001
• Status: Expired due to Fees

• Current Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Original Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Inventors: Chen, Pinhong, Teng, Chin-Chi
• Primary Examiner(s): THOMPSON, ANNETTE M
• Application Number:
  US10/323,399
• Publication Number:
  US 20030140325A1
• Time in Patent Office: 1,315 Days
• Field of Search: 716/6, 716/4
• US Class Current: 716/113
• CPC Class Codes: G06F 30/33 Design verification, e.g. functional simulation or model checking
• CPC Class Codes: G06F 30/367 Design verification, e.g. using simulation, simulation program with integrated circuit emphasis [SPICE], direct methods or relaxation methods

Abstract

To estimate path delays within an IC, a serial database is first created to hold and read out RC extraction data for nets within the IC in an order in which the RC extraction data will be needed when estimating path delays. Thereafter, as the RC extraction data is sequentially read out of the database for each net, the path delay though each section of the net is computed and added to the estimated path delay for each signal path including that net section. The RC extraction data for each net is accessed and accessed only once, thereby minimizing the processing time needed to perform timing analysis by minimizing hard disk read accesses when the RC extraction database resides on a hard disk.

Claims

1. A method for generating path delay data representing an estimated signal path delay through each of a plurality of signal paths within an integrated circuit (IC), wherein the IC includes a plurality of cells and a plurality of nets for conveying signals between the cells, the method comprising the steps of:

a. selecting one of the nets;

b. reading RC extraction data indicating an estimated impedance of each section of the net selected at step a from a database storing RC extraction data indicating an estimated impedance of each section of each of the plurality of nets, and computing as a function of the read RC extraction data, an estimated path delay through each section of the net selected at step a that is included in at least one of the plurality of signal paths; and

c. adjusting the path delay data for each one of the plurality of signal paths that includes a section of the net selected at step a by incrementing an estimated signal path delay that the path delay data represents by an amount of the estimated path delay through that section of the net computed at step b.

2. The method in accordance with claim 1 further comprising the step of:

d. repeating steps a through c in succession a plurality of times with a separate one of the plurality of nets being selected at step a during each repetition of steps a through c.

3. The method in accordance with claim 2 wherein at least one of the plurality of signal paths also includes at least one of the plurality of cells, and wherein the method further comprises the steps of:

e. determining an estimated path delay through each of the plurality of cells included in at least one of the signal paths of interest, and

f. for each one of the signal paths, adjusting the path delay data representing the path delay in that signal path to increment the path delay it represents by an amount equal to an estimated path delay determined at step d of each one of the plurality of cells included in that signal path.

4. The method in accordance with claim 1 further comprising the step of:

d. repeating steps a through c in succession once for each of the plurality of nets with a separate one of the plurality of nets being selected at step a during each repetition of steps a through c.

5. The method in accordance with claim 4 further comprising the step of

e. prior to step a, generating the database, wherein the database is a serial database that stores RC extraction data as a data sequence and reads out the RC extraction data only in an order in which it appears in the stored data sequence.

6. The method in accordance with claim 5 wherein the RC extraction database resides on a hard disk during each repetition of step a.

7. The method in accordance with claim 4 wherein each net conveys a separate signal, and wherein each cell receives at least one input signal conveyed on at least one of the nets and generates at least one output signal of a state affected by the cell'"'"'s at least one input signal, the output signal being conveyed on at least one other of the nets, and

wherein nets are selected during successive repetitions of step a in an order such that each particular net is selected only after all other nets conveying signals affecting states of the signal conveyed by the particular net have been selected.

8. The method in accordance with claim 7 further comprising the step of:

e. prior to step a, generating the database, wherein the database is a serial database that stores RC extraction data as a data sequence and reads out the RC extraction data only in an order in which it appears in the stored data sequence.

9. Computer readable media storing software which when read and executed by a computer, causes the computer to carry out a method for generating path delay data representing an estimated signal path delay through each of a plurality of signal paths within an integrated circuit (IC), wherein the IC includes a plurality of cells and a plurality of nets for conveying signals between the cells, wherein the method comprises the steps of:

a. selecting one of the nets,

b. reading RC extraction data indicating an estimated impedance of each section of the net selected at step a from a database storing RC extraction data indicating an estimating impedance of each section of each of the plurality of nets, and computing as a function of the read RC extraction data, an estimated path delay through each section of the net selected at step a that is included in at least one of the plurality of signal paths; and

c. adjusting the path delay data for each one of the plurality of signal paths that includes a section of the net selected at step a by incrementing an estimated signal path delay that the path delay data represents by an amount of the estimated path delay through that section of the net computed at step b.

10. The computer readable media in accordance with claim 9 where the method further comprises the step of:

d. repeating steps a through c in succession a plurality of times with a separate one of the plurality of nets being selected at step a during each repetition of steps a through c.

11. The computer readable media in accordance with claim 10 wherein the method further comprises the step of:

d. repeating steps a through c in succession once for each of the plurality of nets with a separate one of the plurality of nets being selected at step a during each repetition of steps a through c.

12. The computer readable media in accordance with claim 11 wherein the method further comprises the step of:

e. prior to step a, generating the database, wherein the database is a serial database that stores RC extraction data as a data sequence and reads out the RC extraction data only in an order in which it appears in the stored data sequence.

13. The computer readable media in accordance with claim 12 wherein the RC extraction database resides on a hard disk accessed by the computer during each repetition of step a.

14. The computer readable media in accordance with claim 11

wherein each net conveys a separate signal, and

wherein each cell receives at least one input signal conveyed on at least one of the nets and generates at least one output signal of a state affected by the cell'"'"'s at least one input signal, the output signal being conveyed on at least one other of the nets,

wherein nets are selected during successive repetitions of step a in an order such that each particular net is selected only after all other nets conveying signals affecting states of the signal conveyed by the particular net have been selected.

15. The computer readable media in accordance with claim 14 wherein the method further comprises the step of:

e. prior to step a, generating the database, wherein the database is a serial database that store RC extraction data as a data sequence and reads out the RC extraction data only in an order in which it appears in the stored data sequence.

16. The computer readable media in accordance with claim 10 wherein at least one of the plurality of signal paths also includes at least one of the plurality of cells, and wherein the method further comprises the steps of:

e. determining an estimated path delay through each of the plurality of cells included in at least one of the signal paths of interest, and

f. for each one of the signal paths, adjusting the path delay data representing the path delay in that signal path by incrementing the path delay it represents by an amount equal to an estimated path delay determined at step d of each one of the plurality of cells included in that signal path.