Power Analysis

rb power runs OpenROAD report_power on a mapped design and reports total, internal, switching, and leakage power. FPGA runs report Vivado power directly; they do not use this command.

Choose the design source

Source	Input	Timing and parasitics	Required upstream runs
netlist-source: synth	synth_netlist.v	User SDC, no wire parasitics or clock tree	rb synth
netlist-source: pnr	<top>.routed.odb	Routed SDC, CTS, and global-routing parasitic estimates	rb synth, then rb pnr

The default synth source is useful for early leakage and activity comparisons but underestimates switching because it has no routed wire capacitance. Use pnr for a more representative post-route estimate.

If the routed ODB is missing, rerun rb pnr.

Install OpenROAD

OpenROAD 25Q1 or newer must be on PATH or configured under cfg-power-tools. Power runs currently support only tool: openroad; unsupported tools report SKIP.

The selected cfg-pnr-platforms entry supplies the PDK and Liberty corner. See Place-and-Route.

Define power runs

rtl-buddy-filetype: power_config

runs:
  - name: demo_power_static
    desc: Static post-synthesis power
    tool: openroad
    mode: static
    synth: demo_synth_nangate45
    synth-path: ../../synth/demo/synth.yaml
    constraints: ../../synth/demo/constraints.sdc
    platform: nangate45_typ
    reglvl: 1000

  - name: demo_power_saif
    desc: Simulation-driven post-route power
    tool: openroad
    mode: dynamic
    netlist-source: pnr
    pnr: demo_pnr_nangate45
    pnr-path: ../../pnr/demo/pnr.yaml
    platform: nangate45_typ
    activity:
      saif: ../../verif/demo/artefacts/csr_smoke/dump.saif
      scope: tb_top/u_dut
    reglvl: 1000

Paths resolve from power.yaml. A synth-source run requires synth, synth-path, and constraints. A P&R-source run requires pnr and pnr-path; it uses the routed SDC unless constraints overrides it.

See YAML Formats: power.yaml for all fields.

Select activity

Mode and fields	Applied activity
mode: static	No activity command
mode: dynamic with activity.saif	Per-signal SAIF activity
mode: dynamic with activity.vcd	Per-signal VCD activity
mode: dynamic with no trace	Global synthetic toggle rate and static probability

activity.saif and activity.vcd are mutually exclusive. Set activity.scope only with a trace; use the hierarchy containing the design, such as tb_top/u_dut.

Synthetic defaults are a 0.1 toggle rate and 0.5 static probability. Override them with activity.default-toggle-rate and activity.default-static-prob.

Capture SAIF activity

Convert a debug waveform with the built-in rb saif command:

rb -M debug test csr_smoke
rb saif verif/demo/artefacts/csr_smoke/dump.fst \
  verif/demo/artefacts/csr_smoke/dump.saif
rb power demo_power_saif -c power/demo/power.yaml -l 1000

The converter accepts FST or VCD and writes SAIF v2.0. If the trace starts at the testbench, configure activity.scope so OpenROAD can map the design top.

Run power analysis

rb power --list -c power/demo/power.yaml
rb power demo_power_saif -c power/demo/power.yaml
rb power -c power/demo/power.yaml -l 1000
rb power-regression -c power_regression.yaml -l 1000

A regression manifest lists power configs relative to itself:

rtl-buddy-filetype: power_reg_config
power-configs:
  - power/block_a/power.yaml
  - power/block_b/power.yaml

Interpret results

The summary identifies the selected design source and resolved activity source, then reports total, internal, switching, and leakage power with readable SI scaling.

A run passes when OpenROAD exits 0, emits no [ERROR ...] line, and produces a parseable Total row in power.rpt. It skips when filtered by reglvl or when its tool has no registered backend.

Inspect artefacts

Outputs land under <power-dir>/artefacts/<run>/:

File	Purpose
power.tcl	Generated OpenROAD script
power.log	OpenROAD output
power.rpt	Raw report_power report

An FPGA run and a power run must not share a name within one suite: both own artefacts/<name>/power.rpt and the second to run overwrites the first. Ownership cannot be told apart by filename, so rtl_buddy does not try — give them distinct names.

On failure, inspect power.log for tool and input errors, then power.rpt for missing or malformed totals. power.rpt is deleted before each run and again if the run fails after writing it, so a run that never got as far as report_power — or that reached it and then failed — leaves none — read power.log in that case rather than an earlier run's numbers. A run that cannot find its backend tool is the exception: it deletes nothing, because a machine without the tool never ran it and has no business removing what a machine that has it produced.