Physical design can only use what the handoff carries. A missing piece is rebuilt by guesswork, and guesswork reopens closed timing.
Item | Contents | Consumer |
|---|---|---|
Gate-level netlist | Mapped cells and wires, no behavioural constructs | Placement and routing |
Timing constraints | Clocks, IO delays, exceptions in SDC style | Placement, clock tree, signoff |
Library views | Timing, area, and physical views of every cell used | Every downstream tool |
Scan definition | Chains, order, clocking, and test modes | Scan stitching and test |
Reports | Area, timing, and quality snapshots with the run script | Review and debug |
The sketch below is illustrative only, not tool syntax. It shows the intent each constraint carries into physical design.
illustrative sketch, not tool syntax:
create_clock -period 2.0 on the clock port
set_input_delay 0.4 relative to that clock on all inputs
set_output_delay 0.4 relative to that clock on all outputs
false paths on reset and test-mode selectsEvery handoff answers each row before the netlist leaves. An unchecked row is a named owner and a date, never a shrug.
Check | Done means | If missing |
|---|---|---|
Netlist matches constraints version | Same revision on both, recorded | IO timed against the wrong logic |
Every clock constrained | Each clock created with period and source | Untimed paths found at signoff |
Every IO delayed or excepted | Input and output delay, or a false or multicycle path | Route optimises the wrong paths |
Scan chains defined | Order, clocks, and modes written down | Stitching reorders or breaks timing |
Library views match cells | No cell without timing and physical views | Tool substitutes or stops |
Reports archived | Area, timing, runs reproducible from the script | Debug starts from rumour |
The classic failure is a stale constraint file beside a fresh netlist. Names drift, new ports arrive unconstrained, and the router polishes paths nobody cares about.
An input or output delay on it, or a documented exception. Unconstrained means untimed.
Stitching order and test-mode timing get invented downstream. Scan definition belongs in the handoff.