PDK / Process Technology Migration

Migrate Virtuoso/Spectre simulation setups to a new process node or PDK version.

Migration target: $ARGUMENTS

If the argument above is non-empty, use it as the source/target context throughout (e.g. tailor corner name examples to the specific foundries). If it is empty, ask the user for the old PDK and the new PDK before proceeding.

The workflow has six phases. Work through them in order — auditing first prevents broken partial migrations.

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Phase 1: Audit — catalog all PDK-specific references

Before changing anything, understand the full scope.

Find model file references in existing Ocean/netlists

Check generated netlists and Ocean setup scripts for model references.

Use the Grep tool on *.scs, *.ocn, *.il files under the project root for:

• include "...\.lib" — model file paths
• modelFile( — Ocean setup calls
• Section names (e.g., section=tt, "ff", "ss")

Record: old model path, old section names, technology name in path.

List active design variables

vcli maestro list-vars --format json
# — or if no Maestro session —
vcli skill exec 'paramList()' --format json

Note all variables that encode process assumptions: L, Lmin, vdd, vth_ref, supply names. These often need updating when nodes change.

Check Maestro session corners

vcli maestro list-sessions --format json
vcli skill exec 'let((sess) sess=axlGetWindowSession(hiGetCurrentWindow()) maeGetSetup(?session sess))' --format json

Open the Maestro GUI and note every corner's model file path and section name — these are stored in the .sdb and won't migrate automatically.

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Phase 2: Corner name mapping

Create a mapping table before changing anything:

Old section  →  New section
────────────────────────────
tt           →  TT  (or "typical")
ff           →  FF
ss           →  SS
fnsp         →  FS
snfp         →  SF

If the new PDK's section names are unknown, read its model file header:

head -80 /path/to/new_pdk/models/corner.lib | grep -E "^\.lib|^section"

Section names appear after .lib keywords in SPICE-format files, or after section in Spectre-format files.

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Phase 3: Update model file paths

Ocean / ADE setup scripts

Replace the old modelFile() call with the new PDK path and updated section names:

vcli skill exec 'modelFile(
  list("/new/pdk/path/models.lib" "TT")
  list("/new/pdk/path/models.lib" "res_TT")
)' --format json

Critical: never include an entry with an empty section name "" for .lib files — Spectre fails with SFE-675. Only .ckt files accept an empty section.

Standalone .scs netlists

Edit include statements directly:

// Old:
include "/smic28hpc/models/corner.lib" section=tt

// New:
include "/tsmc40lp/models/corner.lib" section=TT

Use Grep + Edit to find all occurrences across testbench files.

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Phase 4: Design variable migration

Update process-sensitive variables for the new node. Common differences:

Variable	Example: 28nm → 40nm	Notes
L / Lmin	28e-9 → 40e-9	Confirm with PDK spec
vdd	0.9 V → 1.1 V	Check PDK nominal supply
vth_n / vth_p	node-dependent	Read from model param statement
Bias resistor R	may need rescaling	Keep same bias current, adjust R

Update each variable:

vcli maestro set-var --name Lmin --value 40e-9
vcli maestro set-var --name vdd  --value 1.1

Or via SKILL if no active Maestro session:

vcli skill exec 'desVar("Lmin" 40e-9)' --format json
vcli skill exec 'desVar("vdd" 1.1)' --format json

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Phase 5: Maestro session re-setup

Maestro .sdb stores absolute model paths — these don't transfer across PDK installations. The recommended approach:

1. Open the Maestro/ADE Assembler window in editing mode.
2. Go to Setup → Model Files (or equivalent in your IC version).
3. Delete all old model file entries.
4. Add new entries using the new PDK path and the mapped section names.
5. Save: vcli maestro save --session <sessionName>

For scripted re-entry (large corner sets), use modelFile() in an Ocean batch script and call it before each run — Ocean model state doesn't persist across sessions, so re-applying at run time is safer than trying to patch the .sdb.

Verify corners are applied

Check the next generated netlist (input.scs) for the include lines — these reflect what Spectre actually sees. If an old path appears there, Maestro is still using a cached value: save the session and regenerate the netlist.

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Phase 6: Re-netlist and validate

# Force re-netlist from schematic
vcli sim netlist --lib MYLIB --cell MYCELL

# DC operating point
vcli sim run --analysis dc --param saveOppoint=t --timeout 120

# Spot-check a key node
vcli skill exec 'value(getData("/VOUT" ?result "dcOpInfo"))' --format json

# Check bias current
vcli skill exec 'value(getData("/I_bias:id" ?result "dcOpInfo"))' --format json

Expected shifts after a node migration: Ibias ±20–30% (due to different µCox, Vth), gm/Id curve shifted along x-axis. Larger deviations suggest a wrong model section or missing design variable update.

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Common Pitfalls

Symptom	Likely cause	Fix
SFE-675	Empty "" section in modelFile()	Remove blank-section entry
All corners give identical results	Section name mapping wrong — all resolve to same model	Verify section names in new PDK .lib header
Ibias off by 10×	L not updated — PDK default changed	Update desVar("L" ...) to new Lmin
design() returns nil after migration	Model path includes oa/ symlink that broke	Use direct absolute PDK path
Maestro runs but results unchanged	Old .sdb model paths still active — didn't re-enter corners	Re-enter via Setup → Model Files and save
SFE-30 on ac=1 in vsource	Syntax unchanged but now in native Spectre mode	Change to mag=1 — see /spectre-netlist-gotchas

For netlisting nil / OSSHNL errors after migration, see /ocean-netlist-regen. For SFE-30, oprobe noise, PSF parse errors, see /spectre-netlist-gotchas. For re-running simulations after migration, see /sim-setup and /sim-run.