PD Tool Knowledge
The place-and-route tools: what a PnR tool runs, Cadence Innovus and Synopsys ICC2/Fusion command flows, OpenROAD/OpenLane, and how to compare them.
Physical design is run inside a place-and-route (PnR) tool: you hand it the synthesized gate-level netlist, the timing constraints (SDC) and the physical libraries (.lef), and it drives every stage from floorplan to a tape-out-ready GDSII. Two commercial flows dominate the industry, Cadence and Synopsys, alongside a capable open-source flow. Knowing which tool does what, and the shape of its commands, is part of being fluent in physical design.
What a PD tool actually runs
Whatever the vendor, a PnR tool runs the same backbone of stages: read the netlist and libraries, build the floorplan and power grid, place the standard cells, synthesize the clock tree, route the nets, and optimise timing, power and area continuously across all of it before signoff. The commands differ; the flow does not.
Cadence Innovus
Innovus is Cadence's implementation system, paired upstream with the Genus synthesis engine. The two share a common command interface (the Stylus UI), so constraints and scripts carry cleanly from synthesis into place-and-route. Innovus is known for strong early global routing and congestion handling, and its concurrent clock-and-data optimisation during CTS.
| Innovus command | Stage |
|---|---|
| read_netlist / read_mmmc / read_physical | Read netlist, constraints and libraries |
| create_floorplan / addRing / addStripe | Floorplan and power grid |
| place_opt_design | Placement with optimisation |
| ccopt_design | Clock tree synthesis (concurrent clock + data) |
| routeDesign / earlyGlobalRoute | Global and detailed routing |
| optDesign | Post-route timing / power optimisation |
| streamOut | Write the final GDSII |
Synopsys ICC2 / Fusion Compiler
IC Compiler II (ICC2) is Synopsys's implementation tool, paired with Design Compiler for synthesis. Fusion Compiler is the newer single-tool RTL-to-GDS flow that folds synthesis and PnR into one engine sharing a common data model, reducing the correlation gap between synthesis estimates and the real layout. Both share Synopsys's Tcl command style and the PrimeTime signoff engine.
| ICC2 command | Stage |
|---|---|
| read_verilog / read_parasitic_tech / link_block | Read netlist and set up libraries |
| initialize_floorplan / create_power_straps | Floorplan and power grid |
| place_opt | Placement with optimisation |
| clock_opt | Clock tree synthesis and optimisation |
| route_auto / route_opt | Routing and post-route optimisation |
| report_timing / report_power | Analysis |
| write_gds | Write the final GDSII |
Open source: OpenROAD / OpenLane
OpenROAD is a fully open-source RTL-to-GDS engine, wrapped by OpenLane into a push-button flow on the free Sky130 and other open PDKs. It uses Yosys for synthesis, OpenROAD for placement, CTS (TritonCTS) and routing (TritonRoute), and Magic/KLayout plus Netgen for DRC/LVS. It is how most people learn the full flow hands-on without a commercial licence, and it is the flow behind our OpenLane course.
Choosing and comparing
In practice the tool is dictated by the flow your team already uses, Cadence shops run Genus + Innovus, Synopsys shops run DC/Fusion + ICC2, and both are capable of leading-edge tape-outs. The skills transfer: floorplanning, timing closure, congestion and IR-drop thinking are the same everywhere; only the command names change.
| Cadence Innovus | Synopsys ICC2 / Fusion | |
|---|---|---|
| Synthesis partner | Genus | Design Compiler / Fusion Compiler |
| Signoff STA | Tempus | PrimeTime |
| Signoff extraction | Quantus | StarRC |
| Command style | Common UI (Stylus), Tcl | Tcl |
| Noted strength | Global route / congestion, ccopt | RTL-to-GDS data model (Fusion), PT signoff |
Recap: a PnR tool takes the netlist, SDC and physical libraries and runs the whole backend: floorplan, power, place, CTS, route, optimise, signoff. Cadence (Genus -> Innovus, Tempus/Quantus) and Synopsys (DC/Fusion -> ICC2, PrimeTime/StarRC) are the two commercial flows; OpenROAD/OpenLane is the open-source route. The commands change, the flow and the skills do not.