Quartus® Prime Pro Edition User Guide: Timing Analyzer

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ID 683243
Date 9/30/2024
Public
Document Table of Contents
Document Table of Contents x
Answers to Top FAQs 1. Timing Analysis Introduction 2. Using the Quartus® Prime Timing Analyzer A. Quartus® Prime Pro Edition User Guides
1. Timing Analysis Introduction x
1.1. What's New In This Version 1.2. Timing Analysis Basic Concepts 1.3. Timing Analysis Overview Document Revision History
1.2. Timing Analysis Basic Concepts x
1.2.1. Timing Path and Clock Analysis 1.2.2. Clock Setup Analysis 1.2.3. Clock Hold Analysis 1.2.4. Recovery and Removal Analysis 1.2.5. Multicycle Path Analysis 1.2.6. Metastability Analysis 1.2.7. Timing Pessimism 1.2.8. Clock-As-Data Analysis 1.2.9. Multicorner Timing Analysis 1.2.10. Time Borrowing
1.2.1. Timing Path and Clock Analysis x
1.2.1.1. The Timing Netlist 1.2.1.2. Timing Paths 1.2.1.3. Data and Clock Arrival Times 1.2.1.4. Launch and Latch Edges
1.2.5. Multicycle Path Analysis x
1.2.5.1. Multicycle Clock Hold 1.2.5.2. Multicycle Clock Setup
1.2.10. Time Borrowing x
1.2.10.1. Time Borrowing Limitations 1.2.10.2. Time Borrowing with Latches 1.2.10.3. Enabling Time Borrowing Optimization
2. Using the Quartus® Prime Timing Analyzer x
2.1. Using Timing Constraints throughout the Design Flow 2.2. Timing Analysis Flow 2.3. Applying Timing Constraints 2.4. Timing Constraint Descriptions 2.5. Timing Report Descriptions 2.6. Scripting Timing Analysis 2.7. Using the Quartus® Prime Timing Analyzer Document Revision History 2.8. Quartus® Prime Pro Edition User Guide: Timing Analyzer Archive
2.2. Timing Analysis Flow x
2.2.1. Step 1: Specify General Timing Analyzer Settings 2.2.2. Step 2: Specify Timing Constraints 2.2.3. Step 3: Run the Timing Analyzer 2.2.4. Step 4: Analyze Timing Reports
2.2.2. Step 2: Specify Timing Constraints x
2.2.2.1. Specifying SDC-on-RTL Timing Constraints 2.2.2.2. Specifying Conventional SDC Timing Constraints 2.2.2.3. Specifying Synthesis-Only SDC Timing Constraints
2.2.3. Step 3: Run the Timing Analyzer x
2.2.3.1. Running Post-Synthesis Early Timing Analysis 2.2.3.2. Running Post-Fit Timing Analysis
2.2.3.2. Running Post-Fit Timing Analysis x
2.2.3.2.1. Setting the Operating Conditions for Timing Analysis 2.2.3.2.2. Promoting Critical Warnings to Errors
2.2.4. Step 4: Analyze Timing Reports x
2.2.4.1. Cross-Probing with Design Assistant 2.2.4.2. Launching Design Assistant from Timing Analyzer 2.2.4.3. Locating Timing Paths in Other Tools 2.2.4.4. Correlating Constraints to the Timing Report
2.2.4.1. Cross-Probing with Design Assistant x
2.2.4.1.1. Cross-Probing from Design Assistant to Timing Analyzer
2.3. Applying Timing Constraints x
2.3.1. Recommended Initial Conventional SDC Constraints 2.3.2. Example Circuit and Conventional SDC File 2.3.3. SDC File Precedence 2.3.4. Iteratively Modifying Constraints 2.3.5. Applying Entity-Bound Timing Constraints 2.3.6. Constraining Design Partition Ports 2.3.7. Using Fitter Overconstraints
2.3.1. Recommended Initial Conventional SDC Constraints x
2.3.1.1. Create Clock (create_clock) 2.3.1.2. Derive PLL Clocks (derive_pll_clocks) 2.3.1.3. Derive Clock Uncertainty (derive_clock_uncertainty) 2.3.1.4. Set Clock Groups (set_clock_groups)
2.3.5. Applying Entity-Bound Timing Constraints x
2.3.5.1. Using Entity-Based SDC-on-RTL Constraints 2.3.5.2. Using Entity-Bound SDC Files
2.3.5.1. Using Entity-Based SDC-on-RTL Constraints x
2.3.5.1.1. Targeting Constraints to Module Inputs and Outputs 2.3.5.1.2. Entity Based SDC-on-RTL Constraint Scope 2.3.5.1.3. Automatic Scope Example for SDC-on-RTL 2.3.5.1.4. Manual Scope Example for SDC-on-RTL
2.3.5.2. Using Entity-Bound SDC Files x
2.3.5.2.1. Entity-Bound SDC Constraint Scope 2.3.5.2.2. Automatic Scope Entity-bound Constraint Example 2.3.5.2.3. Manual Scope Entity-bound Constraint Example 2.3.5.2.4. Exporting a Design Partition with Entity-bound Constraints 2.3.5.2.5. Importing a Design Partition with Entity-bound Constraints
2.3.6. Constraining Design Partition Ports x
2.3.6.1. Timing Analysis of Imported Compilation Results
2.4. Timing Constraint Descriptions x
2.4.1. Clock Constraints 2.4.2. I/O Constraints 2.4.3. Delay and Skew Constraints 2.4.4. Timing Exception Constraints 2.4.5. Delay Annotation
2.4.1. Clock Constraints x
2.4.1.1. Creating Base Clocks 2.4.1.2. Creating Virtual Clocks 2.4.1.3. Creating Generated Clocks (create_generated_clock) 2.4.1.4. Deriving PLL Clocks 2.4.1.5. Creating Clock Groups (set_clock_groups) 2.4.1.6. Accounting for Clock Effect Characteristics 2.4.1.7. Constraining CDC Paths
2.4.1.1. Creating Base Clocks x
2.4.1.1.1. Automatic Clock Detection and Constraint Creation
2.4.1.2. Creating Virtual Clocks x
2.4.1.2.1. Specifying I/O Interface Uncertainty 2.4.1.2.2. I/O Interface Clock Uncertainty Example
2.4.1.3. Creating Generated Clocks (create_generated_clock) x
2.4.1.3.1. Clock Divider Example (-divide_by) 2.4.1.3.2. Clock Multiplexer Example
2.4.1.5. Creating Clock Groups (set_clock_groups) x
2.4.1.5.1. Exclusive Clock Groups (-logically_exclusive or -physically_exclusive) 2.4.1.5.2. Asynchronous Clock Groups (-asynchronous) 2.4.1.5.3. set_clock_groups Constraint Tips
2.4.1.6. Accounting for Clock Effect Characteristics x
2.4.1.6.1. Set Clock Latency (set_clock_latency) 2.4.1.6.2. Clock Uncertainty
2.4.2. I/O Constraints x
2.4.2.1. Deprecation of the blackbox Argument 2.4.2.2. Input Constraints (set_input_delay) 2.4.2.3. Output Constraints (set_output_delay)
2.4.3. Delay and Skew Constraints x
2.4.3.1. Advanced I/O Timing and Board Trace Model Delay 2.4.3.2. Maximum Skew (set_max_skew) 2.4.3.3. Net Delay (set_net_delay) 2.4.3.4. Data Delay (set_data_delay)
2.4.4. Timing Exception Constraints x
2.4.4.1. Timing Exception Precedence 2.4.4.2. False Paths (set_false_path) 2.4.4.3. Minimum and Maximum Delays 2.4.4.4. Multicycle Paths 2.4.4.5. Multicycle Exception Examples 2.4.4.6. Creating Efficient Timing Exceptions
2.4.4.4. Multicycle Paths x
2.4.4.4.1. Common Multicycle Applications 2.4.4.4.2. Relaxing Setup with Multicycle (set_multicyle_path) 2.4.4.4.3. Accounting for a Phase Shift (-phase)
2.4.4.5. Multicycle Exception Examples x
2.4.4.5.1. Default Multicycle Analysis 2.4.4.5.2. End Multicycle Setup = 2 and End Multicycle Hold = 0 2.4.4.5.3. End Multicycle Setup = 2 and End Multicycle Hold = 1 2.4.4.5.4. Same Frequency Clocks with Destination Clock Offset 2.4.4.5.5. Destination Clock Frequency is a Multiple of the Source Clock Frequency 2.4.4.5.6. Destination Clock Frequency is a Multiple of the Source Clock Frequency with an Offset 2.4.4.5.7. Source Clock Frequency is a Multiple of the Destination Clock Frequency 2.4.4.5.8. Source Clock Frequency is a Multiple of the Destination Clock Frequency with an Offset
2.5. Timing Report Descriptions x
2.5.1. Report Fmax Summary 2.5.2. Report Timing 2.5.3. Report Timing By Source Files 2.5.4. Report Data Delay 2.5.5. Report Net Delay 2.5.6. Report Clocks and Clock Network 2.5.7. Report Clock Transfers 2.5.8. Report Metastability 2.5.9. Report CDC Viewer 2.5.10. Report Asynchronous CDC 2.5.11. Report Logic Depth 2.5.12. Report Neighbor Paths 2.5.13. Report Register Spread 2.5.14. Report Route Net of Interest 2.5.15. Report Retiming Restrictions 2.5.16. Report Register Statistics 2.5.17. Report Pipelining Information 2.5.18. Report Time Borrowing Data 2.5.19. Report Exceptions and Exceptions Reachability 2.5.20. Report Bottlenecks 2.5.21. Check Timing 2.5.22. Report SDC
2.5.13. Report Register Spread x
2.5.13.1. Registers with High Timing Path Endpoint Tension 2.5.13.2. Registers with High Immediate Fan-Out Tension
2.5.20. Report Bottlenecks x
2.5.20.1. Specifying Custom Bottleneck Criteria
2.6. Scripting Timing Analysis x
2.6.1. The quartus_sta Executable 2.6.2. The quartus_staw Executable 2.6.3. Collection Commands
2.6.3. Collection Commands x
2.6.3.1. Wildcard Characters 2.6.3.2. Adding and Removing Collection Items 2.6.3.3. Query of Collections 2.6.3.4. Using the get_pins Command
Answers to Top FAQs
1. Timing Analysis Introduction
2. Using the Quartus® Prime Timing Analyzer
A. Quartus® Prime Pro Edition User Guides

1.2.10.2. Time Borrowing with Latches

The Quartus® Prime Timing Analyzer treats level-sensitive latches similar to registers. The Timing Analyzer treats the latch enable pin as a clock pin, while modifying the clock relationship appropriately.

You can run Reports > Constraint Diagnostics > Check Timing in the Timing Analyzer Tasks pane to view a list of the level-sensitive latches in your design.

Implementation of latch time borrowing requires that you enable Dynamic borrowing mode (update_timing_netlist -dynamic_borrow). Otherwise, the Timing Analyzer calculates zero time borrowing for latches. In Dynamic mode, the Timing Analyzer simply reports the amount of time borrowing that would physically happen in the circuit, given the clock frequencies you specify in SDC constraints, and does not actually optimize borrowing in any way.

For latches, the setup relationship is to the opening edge of the latch, which allows time borrowing. The hold relationship is to the closing edge of the latch. For example, a path from a positive register to another positive register has a default setup clock relationship of one clock period. A path from a positive register to a positive (open-high), level-sensitive latch has a default setup clock relationship of zero clock periods, plus any time borrow value.

The Timing Analyzer treats paths to and from a latch as two separate paths. For example, in a positive register--> positive latch--> negative register transfer, the Timing Analyzer does not analyze the overall register-->register transfer, even though you expect the latch to be transparent for the entire duration of the transfer. The Timing Analyzer analyzes and reports the paths to and from the latch separately.

The Timing Analyzer automatically computes the maximum amount of time borrowing available for each latch. Typically, the maximum amount of time borrowing available is roughly equivalent to half the clock period. The exact amount of time borrowing available is based on:

  • The timing of opening and closing latch edges
  • Physical latch implementation (closing-edge µtSU of the latch)
  • Clock uncertainty and other effects

The time borrowing never exceeds the maximum borrow value. However, you can specify a smaller maximum borrow time with the set_max_time_borrow SDC constraint. For example: 

#Borrow at most 3ns at all "lat*" latches: 
set_max_time_borrow 3 [get_registers lat*]

Specifying a clock with a negative borrow window can result in negative maximum borrowable time, which is equivalent to a minimum pulse width violation. For example, this condition can occur if half the clock period is smaller than the closing-edge µtSU of the latch. If such a violation occurs, a warning indicates that the design cannot pass timing.

Note: Whether you use time borrowing or not, do not rely on the timing analysis Fmax Summary report for any clock domains with latches. The Fmax Summary values for such clock domains include no borrowing, and are therefore significantly pessimistic.
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