Place-and-Route

Integration type: Integrated tool. rb pnr is built around OpenROAD today.

External binary required: openroad ≥ 25Q1 — see Installing OpenROAD.

Optional: klayout for --gds / --png streamout and rendering — see Installing KLayout.

See also: Installation — External tools by feature.

rb pnr drives OpenROAD through a templated Tcl flow that consumes the tech-mapped netlist from an upstream rb synth run. It produces routed DEF, a post-route netlist + SDC, a timing report, and a DRC report under pnr/<run>/artefacts/.

The flow is intentionally compact and config-driven — block-level knobs live in pnr.yaml, technology-level knobs live in cfg-pdks + cfg-pnr-platforms in root_config.yaml.

Supported backend

Today only openroad is wired up. The tool: field in pnr.yaml selects it; the runner skips any other value with a clear message.

Installing OpenROAD

openroad must be on PATH, or its absolute path must be configured via a cfg-pnr-tools entry in root_config.yaml (see yaml.md). Build from source (no official macOS binaries):

ln -s /path/to/OpenROAD/build/bin/openroad /usr/local/bin/openroad

See tools/openroad/BUILD_OSX.md in the project template for the macOS recipe.

Version expectations

rb pnr probes openroad -version and compares it against an internal MIN_OPENROAD_VERSION (currently 25Q1). Older builds may still work for the basic flow but are unvalidated — a pnr.openroad_version_below_min warning is emitted and the run continues. The version is also logged at INFO as pnr.openroad_version so it shows up in rtl_buddy.log.

Installing KLayout (optional)

KLayout is only required when streaming out GDS with --gds or rendering PNGs with --png. The basic P&R flow works without it.

brew install --cask klayout            # macOS
# or download from https://klayout.de

rb pnr resolves klayout from PATH. If KLayout is not present, --gds/--png logs pnr.no_klayout and skips streamout/render without failing the run.

P&R config: `pnr.yaml`

pnr.yaml declares one or more P&R runs. Each entry references an upstream rb synth entry by path + name, an SDC, and a cfg-pnr-platforms name from root_config.yaml:

rtl-buddy-filetype: pnr_config

runs:
  - name: "demo_pnr_nangate45"
    desc: "OpenROAD P&R on Nangate45 typ corner"
    tool: "openroad"
    synth: "demo_synth_nangate45"
    synth-path: "../../synth/demo/synth.yaml"
    constraints: "../../synth/demo/constraints.sdc"
    platform: "nangate45_typ"
    floorplan:
      utilization: 0.55
      aspect: 1.0
      core-margin: 2.0
    reglvl: 1000

Fields

Field	Description
`name`	Run identifier used on the command line and in `artefacts/<name>/`
`desc`	Human-readable description
`tool`	Backend tool name — only `"openroad"` is supported today
`synth`	Name of the upstream `rb synth` entry to consume
`synth-path`	Path to the `synth.yaml` containing `synth`, resolved relative to `pnr.yaml`
`constraints`	SDC path (required), resolved relative to `pnr.yaml`
`platform`	`cfg-pnr-platforms` entry name
`floorplan.utilization`	Core utilization (0–1); 55% is a reasonable default
`floorplan.aspect`	Die aspect ratio; 1.0 = square
`floorplan.core-margin`	Margin in microns between core area and die edge
`reglvl`	Regression level for filtering (same semantics as `rb synth`)

Where inputs come from

The runner reads the upstream synth.yaml to find the tech-mapped netlist at <synth_dir>/artefacts/<synth_name>/synth_netlist.v. The top module is taken from the synth entry's model: field. The SDC and the PDK Liberty/LEF come from constraints: and the selected cfg-pnr-platforms entry respectively — no path duplication.

Root config: `cfg-pdks` and `cfg-pnr-platforms`

PDK assets live in cfg-pdks (per-process, corners as sub-fields — see the synthesis page). cfg-pnr-platforms is the P&R-side selector:

cfg-pnr-platforms:
  - name: "nangate45_typ"
    pdk: "nangate45"
    corner: "typ"
    cts-buffer: "BUF_X4"
    routing-layers:
      signal: "metal2-metal8"
      clock:  "metal4-metal8"

Field	Description
`name`	Referenced by `platform:` in `pnr.yaml`
`pdk`	`cfg-pdks` entry name
`corner`	Corner from the PDK used for STA; defaults to the first declared corner
`cts-buffer`	Standard cell name passed to `clock_tree_synthesis -root_buf` / `-buf_list`
`routing-layers.signal`	Layer range for signal routing (e.g. `metal2-metal8`)
`routing-layers.clock`	Layer range for clock routing (typically higher metals)

Running P&R

# All runs in the default ./pnr.yaml
rb pnr

# A single run from a specific config
rb pnr demo_pnr_nangate45 -c pnr/demo/pnr.yaml

# Reglvl-gated runs (set reglvl: 1000 in pnr.yaml to gate a run behind -l 1000;
# an unset reglvl defaults to 0, so by default a run executes at -l 0)
rb pnr demo_pnr_nangate45 -c pnr/demo/pnr.yaml -l 1000

# List runs without executing
rb pnr -c pnr/demo/pnr.yaml --list

# Stream out a routed GDS via KLayout after the run
rb pnr demo_pnr_nangate45 -c pnr/demo/pnr.yaml --gds

# Render a PNG of the GDS (implies --gds)
rb pnr demo_pnr_nangate45 -c pnr/demo/pnr.yaml --png

`--gds` and `--png`

When --gds is requested, rb pnr invokes KLayout headlessly after a successful OpenROAD run, merging the routed DEF with the PDK's standard cell GDS to produce artefacts/<run>/<design>.gds. --png additionally renders a 2048×2048 PNG via the bundled gds2png.py helper. Both helpers ship inside the wheel under rtl_buddy/pnr/klayout/ and are copied into the artefact dir at run time. KLayout failures emit pnr.gds_failed / pnr.png_failed warnings but do not fail the P&R run — timing/DRC metrics remain authoritative.

Results table

A summary table prints after each run:

                              P&R Results Summary
┏━━━━━━━━━━┳━━━━━━━━┳━━━━━━━━━━┳━━━━━━━┳━━━━━━━━━┳━━━━━━━━━━┳━━━━━━━━━━┳━━━━━━┓
┃ P&R Run  ┃ Result ┃ Desc     ┃ Cells ┃ Area    ┃ WNS Setup┃ WNS Hold ┃ DRCs ┃
┡━━━━━━━━━━╇━━━━━━━━╇━━━━━━━━━━╇━━━━━━━╇━━━━━━━━━╇━━━━━━━━━━╇━━━━━━━━━━╇━━━━━━┩
│ demo_…   │ PASS   │ P&R …    │ 1392  │ 3213 µm²│ +4.350 ns│ +0.080 ns│ 0    │
└──────────┴────────┴──────────┴───────┴─────────┴──────────┴──────────┴──────┘

Cells — Number of instances from OpenROAD's floorplan log.
Area — Design area … um^2 from report_design_area.
WNS Setup / WNS Hold — report_worst_slack -max / -min.
DRCs — non-empty line count of route.drc.rpt. Zero == clean route.

Artefacts

Per-run outputs land under pnr/<run>/artefacts/:

File	Contents
`pnr.log`	Full OpenROAD log
`pnr.tcl`	Templated Tcl handed to OpenROAD
`<design>.def`	Routed DEF
`<design>.routed.v`	Post-route gate-level netlist
`<design>.routed.sdc`	Post-route SDC
`timing.rpt`	Worst-path timing report (full clock expanded)
`route.drc.rpt`	DRC violations (empty file = clean)
`route.maze.log`	Detail-route maze log
`<design>.gds`	Routed GDS — only when `--gds`/`--png` is set
`<design>.png`	Layout render — only when `--png` is set
`klayout.def2stream.log`	KLayout output for the DEF→GDS step (when used)
`klayout.gds2png.log`	KLayout output for the GDS→PNG render (when used)

Pass/fail detection

A run is PASS when:

openroad exits with code 0.
The log has no [ERROR ...] lines.

Otherwise FAIL is returned with the exit code or error count in the description. SKIP is returned when the run's reglvl is above the -l filter or when tool: is not openroad.

Out of scope (today)

Multi-corner signoff.
Tape-out-grade PPA tuning. The defaults are calibrated for teaching demos and quick PPA sanity checks.

Supported backend​

Installing OpenROAD​

Version expectations​

Installing KLayout (optional)​

P&R config: pnr.yaml​

Fields​

Where inputs come from​

Root config: cfg-pdks and cfg-pnr-platforms​

Running P&R​

--gds and --png​

Results table​

Artefacts​

Pass/fail detection​

Out of scope (today)​