Constraints
Constraints describe the timing environment the implementation must satisfy.
A missing or incorrect constraint can create a clean-looking report for the wrong problem.
set_input_delay models delay outside the chip from the launch device to the input port; it is not internal cell delay.
Logic Synthesis flow
Follow each stage in sequence. Every stage produces information needed by the next.
Constraints—visualized
This technical view uses the actual structures and relationships associated with this stage, followed by its key terms.
Understand every concept
Clock definitions
What it is: Clock definitions is a core concept within Constraints. It describes the information, structure, or analysis engineers use at this stage of the Logic Synthesis flow.
Why it matters: Understanding it helps you interpret the stage correctly, avoid incorrect assumptions, and connect the result to the next implementation or signoff step.
Where it fits: This topic belongs to module 2, Constraints, and its output supports the stages that follow.
Practical example: Engineer workflow: Create primary and generated clocks. set_input_delay models delay outside the chip from the launch device to the input port; it is not internal cell delay.
Input and output delays
What it is: Input and output delays is a core concept within Constraints. It describes the information, structure, or analysis engineers use at this stage of the Logic Synthesis flow.
Why it matters: Understanding it helps you interpret the stage correctly, avoid incorrect assumptions, and connect the result to the next implementation or signoff step.
Where it fits: This topic belongs to module 2, Constraints, and its output supports the stages that follow.
Practical example: Engineer workflow: Model input arrival and output requirements. set_input_delay models delay outside the chip from the launch device to the input port; it is not internal cell delay.
Timing exceptions
What it is: Timing exceptions is a core concept within Constraints. It describes the information, structure, or analysis engineers use at this stage of the Logic Synthesis flow.
Why it matters: Understanding it helps you interpret the stage correctly, avoid incorrect assumptions, and connect the result to the next implementation or signoff step.
Where it fits: This topic belongs to module 2, Constraints, and its output supports the stages that follow.
Practical example: Engineer workflow: Describe clock relationships and uncertainty. set_input_delay models delay outside the chip from the launch device to the input port; it is not internal cell delay.
Work through it step by step
- 1
Clock definitions
Create primary and generated clocks.
- 2
Input and output delays
Model input arrival and output requirements.
- 3
Timing exceptions
Describe clock relationships and uncertainty.
- 4
Clock definitions
Add only functionally valid timing exceptions.
Explore each topic
01Clock definitions
Understand the concept, connect it to the ASIC flow, study the report or behavior it produces, and apply it in a guided exercise. Check the result against the module goal before moving forward.
02Input and output delays
Understand the concept, connect it to the ASIC flow, study the report or behavior it produces, and apply it in a guided exercise. Check the result against the module goal before moving forward.
03Timing exceptions
Understand the concept, connect it to the ASIC flow, study the report or behavior it produces, and apply it in a guided exercise. Check the result against the module goal before moving forward.
Completion checklist
- ✓ All sequential endpoints see a clock
- ✓ I/O delays use the correct reference clock
- ✓ Exceptions have functional justification
- ✓ Unconstrained paths are investigated
Practise with open-source tools
These are official third-party GitHub projects selected for this learning path.