Synopsys
Timing Constraints and Optimization
User Guide
Version D-2010.03, March 2010
®
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Synopsys Timing Constraints and Optimization User Guide, version D-2010.03
ii
Contents
What’s New in This Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
About This Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Customer Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.
Introduction to Synthesis Timing
Static Timing Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Timing Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input and Output Delays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Delay Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flip-Flop and Latch Timing Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Timing Analysis in the Design Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Synopsys Design Constraint (SDC) Commands . . . . . . . . . . . . . . . . . . . . . . . .
Library Timing Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Design Compiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ideal Clocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wire Load Models and Topographical Technology . . . . . . . . . . . . . . . . . . .
Design Partitioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Path Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Register Retiming Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IC Compiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Design Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Placement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clock Tree Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1-2
1-7
1-11
1-12
1-14
1-16
1-19
1-19
1-24
1-26
1-26
1-27
1-29
1-31
1-33
1-34
1-35
1-35
1-37
1-38
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Synopsys Timing Constraints and Optimization User Guide
Synopsys Timing Constraints and Optimization User Guide
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D-2010.03
Timing Analysis After Routing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Synthesis Design Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.
Clocks
Creating Clocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clock Network Effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clock Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Propagated Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ideal Network Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Source Latency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clock Uncertainty. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ideal Clock Transition Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reporting Clock Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Multiple Clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Synchronous Clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Asynchronous Clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exclusive Clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clock Sense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pulse Clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clock-Gating Signal Timing Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Generated Clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Divide-by-2 Generated Clock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Generated Clock Based on Edges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Divide-by Clock Based on Falling Edges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Shifting the Edges of a Generated Clock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Combinational-Only Source Latency Calculation . . . . . . . . . . . . . . . . . . . . . . .
Generated Clock Based on a Non-Unate Master Clock . . . . . . . . . . . . . . . . . .
Estimated I/O Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Calculating I/O Latency for Input Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Calculating I/O Latency for Output Paths. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Propagated Clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.
Timing Paths
Path Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1-39
1-40
2-2
2-3
2-5
2-5
2-6
2-7
2-8
2-11
2-12
2-12
2-14
2-16
2-16
2-18
2-22
2-24
2-29
2-30
2-30
2-31
2-33
2-34
2-35
2-37
2-39
2-40
2-40
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Synopsys Timing Constraints and Optimization User Guide
Version D-2010.03
User Grouping of Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Weight or Cost Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Critical Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reporting Path Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Path Specification Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Through Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rise/Fall From/To Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Default Path Delay Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Path Delay for Flip-Flops Using a Single Clock . . . . . . . . . . . . . . . . . . . . . . . . .
Path Delay for Flip-Flops Using Different Clocks . . . . . . . . . . . . . . . . . . . . . . . .
Setup Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hold Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Single-Cycle Path Analysis Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Timing Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
False Path Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Maximum and Minimum Path Delay Exceptions . . . . . . . . . . . . . . . . . . . . . . . .
Multicycle Path Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifying Exceptions Efficiently . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exception Order of Precedence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exception Type Priority . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Path Specification Priority. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reporting Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removing Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data-to-Data Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifying Data-to-Data Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Generating Timing Reports for Data Checks . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Checks and Clock Domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Library-Based Data Checks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.
Operating Conditions
Operating Condition Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Setting Operating Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating Condition Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Minimum and Maximum Delay Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Min-Max Cell and Net Delay Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3-2
3-2
3-3
3-3
3-4
3-5
3-6
3-9
3-9
3-11
3-12
3-12
3-13
3-15
3-16
3-17
3-18
3-23
3-25
3-25
3-25
3-27
3-27
3-28
3-29
3-31
3-32
3-32
4-2
4-4
4-5
4-7
4-7
Chapter 1: Contents
Contents
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1-v
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