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DFT: add ORFS hooks and scan utilities
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‎doc-DFT-howto.md‎

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# DFT / Scan — Quickstart (Before vs After)
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This is a short “how to run” guide. For implementation details, limitations, and scan-order benchmarks, see `doc-DFT.md`.
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## Before (Baseline: no DFT)
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Run the flow normally:
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- `make -C flow DESIGN_CONFIG=./designs/nangate45/ibex/config.mk FLOW_VARIANT=baseline_no_dft finish`
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## After (DFT Enabled: scan flops + stitched chain)
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Enable the two DFT hook scripts:
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- `POST_FLOORPLAN_TCL=$(pwd)/flow/scripts/dft_scan_post_floorplan.tcl`
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- runs `scan_replace` (functional flops → scan flops)
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- creates scan ports: `scan_enable_0`, `scan_in_0`, `scan_out_0`
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- sets `set_case_analysis 0 [get_ports scan_enable_0]` (functional-mode timing)
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- `PRE_GLOBAL_ROUTE_TCL=$(pwd)/flow/scripts/dft_scan_pre_global_route.tcl`
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- runs `execute_dft_plan` (stitches the scan chain using placement)
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Example:
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- `make -C flow DESIGN_CONFIG=./designs/nangate45/ibex/config.mk FLOW_VARIANT=with_dft POST_FLOORPLAN_TCL=$(pwd)/flow/scripts/dft_scan_post_floorplan.tcl PRE_GLOBAL_ROUTE_TCL=$(pwd)/flow/scripts/dft_scan_pre_global_route.tcl finish`
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## Sanity Checks
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- Report the plan (from OpenROAD, after `scan_replace`):
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- `report_dft_plan -verbose`
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- Validate chain integrity from a finished netlist:
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- `python3 flow/util/scan_chain_validate.py --verilog flow/results/<platform>/<design>/<variant>/6_final.v`
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- Or validate from an ODB (runs `scan_replace` + `execute_dft_plan` in-memory and writes a temp netlist):
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- `python3 flow/util/scan_chain_validate.py --odb flow/results/<platform>/<design>/<variant>/3_5_place_dp.odb --openroad $OPENROAD_EXE --liberty <lib> --sdc flow/results/<platform>/<design>/<variant>/3_place.sdc --ensure-ports --scan-replace --execute-dft-plan`
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## Compare “Before vs After” QoR
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- Routed wirelength / timing: compare `flow/results/<...>/metrics.json` and the OpenROAD/OpenSTA reports between `baseline_no_dft` and `with_dft`.
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- Scan-chain wire metric on a fixed placement (also runs an NN heuristic for comparison):
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- `python3 flow/util/scan_chain_cost.py --scan-replace --nearest-neighbor --openroad $OPENROAD_EXE --liberty <lib> --odb flow/results/<...>/3_5_place_dp.odb --sdc flow/results/<...>/3_place.sdc`
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‎doc-DFT.md‎

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# DFT / Scan in ORFS (OpenROAD-flow-scripts)
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Quickstart: `doc-DFT-howto.md`
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This repo wires OpenROAD’s DFT scan insertion into the ORFS flow via **opt-in** hook scripts, plus utilities to measure scan-chain wirelength and validate scan stitching.
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## Required OpenROAD
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This branch pins the `tools/OpenROAD` submodule to **OpenROAD-clean-DFT**:
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- Base: `7bc521f36a`
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- +1 commit (DFT fixes): `661abebbc3c70c59b4a3991acd176a5cc785f0d4`
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The key point: it works with **vanilla OpenSTA** (no OpenSTA parser patch required).
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## ORFS Flow Integration (Where DFT Happens)
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Two hook scripts are provided:
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- `flow/scripts/dft_scan_post_floorplan.tcl`
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- Intended use: `POST_FLOORPLAN_TCL=$(pwd)/flow/scripts/dft_scan_post_floorplan.tcl`
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- Runs after floorplan, before saving `2_1_floorplan.odb`:
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- `set_dft_config -max_chains 1 -clock_mixing clock_mix`
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- `scan_replace` (functional flops → scan flops)
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- creates scan ports: `scan_enable_0`, `scan_in_0`, `scan_out_0`
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- `set_case_analysis 0 [get_ports scan_enable_0]` (functional-mode timing)
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- `flow/scripts/dft_scan_pre_global_route.tcl`
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- Intended use: `PRE_GLOBAL_ROUTE_TCL=$(pwd)/flow/scripts/dft_scan_pre_global_route.tcl`
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- Runs after CTS, before global routing:
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- `set_dft_config ...` (must match the post-floorplan config)
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- `set_case_analysis 0 [get_ports scan_enable_0]`
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- `execute_dft_plan` (stitches the scan chain using placement)
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Notes:
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- The scripts currently hardcode `-max_chains 1` to keep scan I/O stable for comparisons.
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- `set_case_analysis 0` ensures STA uses functional-mode arcs for scan flops.
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## OpenROAD-side Fixes (Summary)
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The OpenROAD-clean-DFT commit includes the minimum required fixes to make DFT “alive” on top of `7bc521f36a`:
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- Scan pin identification works in vanilla STA (`src/dbSta/src/dbSta.cc`):
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- removes an overly-strict `extPort()` guard
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- adds/uses fallback scan pin inference by common names (`SI/SE/SO`, etc.)
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- DFT correctness fixes and functionality (DFT subsystem):
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- scan stitching fixes (no dropped links)
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- avoids reliance on `sta::TestCell`
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- scan-out fallback behavior
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- includes a small DFT regression (`scan_architect_no_mix_nangate45`)
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## Scan-Ordering Benchmark (OpenROAD vs Nearest-Neighbor)
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`flow/util/scan_chain_cost.py` runs OpenROAD’s `report_dft_plan -verbose`, computes total Manhattan scan-chain length, and can also compute a simple nearest-neighbor (NN) heuristic for comparison.
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Opt/NN results (lower is better; `openroad_over_nn < 1` means OpenROAD is shorter than NN):
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| platform | design | flops | openroad_um | nn_um | openroad_over_nn |
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|---|---|---:|---:|---:|---:|
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| nangate45 | aes | 562 | 3571.680 | 4178.080 | 0.855 |
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| nangate45 | ibex | 1931 | 9197.880 | 10545.640 | 0.872 |
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| nangate45 | jpeg | 4390 | 17903.670 | 20815.750 | 0.860 |
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| asap7 | aes | 562 | 1053.810 | 1222.344 | 0.862 |
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| asap7 | ibex | 273 | 428.652 | 514.404 | 0.833 |
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| asap7 | jpeg | 4325 | 5045.058 | 5709.204 | 0.884 |
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| sky130hd | aes | 562 | 11050.640 | 13137.940 | 0.841 |
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| sky130hd | ibex | 1931 | 21754.680 | 24411.360 | 0.891 |
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| sky130hd | jpeg | 4390 | 50973.380 | 57692.340 | 0.884 |
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Avg `opt/NN` = `0.865` (~`13.5%` shorter than NN).
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Reproduce (single design):
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- `python3 flow/util/scan_chain_cost.py --scan-replace --nearest-neighbor --openroad tools/install/OpenROAD/bin/openroad --liberty flow/platforms/nangate45/lib/NangateOpenCellLibrary_typical.lib --odb flow/results/nangate45/ibex/cmp9_or0db856_rp100_20251229_022425/3_5_place_dp.odb --sdc flow/results/nangate45/ibex/cmp9_or0db856_rp100_20251229_022425/3_place.sdc`
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Notes:
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- ASAP7 needs multiple libs; pass them all, e.g. `--liberty flow/platforms/asap7/lib/NLDM/*_TT_*`.
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## Scan-Chain Integrity Validation (Does It Actually Shift?)
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QoR deltas and plan reports are necessary but not sufficient; we also want a basic structural check that the scan path is one continuous chain from `scan_in_0` to `scan_out_0`.
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- `flow/util/scan_chain_validate.py` validates scan stitching from a gate-level netlist (or from an ODB by writing a temporary netlist via OpenROAD).
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- It treats `assign` + inserted `BUF*/CLKBUF*` as transparent, so post-P&R buffering doesn’t cause false failures.
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Example usage:
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- Validate a finished netlist:
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- `python3 flow/util/scan_chain_validate.py --verilog flow/results/nangate45/ibex/with_dft/6_final.v`
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- Validate from an ODB (writes a temp netlist first):
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- `python3 flow/util/scan_chain_validate.py --odb flow/results/nangate45/ibex/with_dft/6_final.odb --openroad tools/install/OpenROAD/bin/openroad --liberty flow/platforms/nangate45/lib/NangateOpenCellLibrary_typical.lib --sdc flow/results/nangate45/ibex/with_dft/6_final.sdc --ensure-ports`
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‎flow/scripts/dft_scan_post_floorplan.tcl‎

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# DFT scan insertion hook for ORFS.
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#
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# Intended use: set `POST_FLOORPLAN_TCL` to this file.
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#
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# This runs after floorplan, before saving `2_1_floorplan.odb`, so subsequent
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# stages (place/cts/route) see scan flops and scan ports.
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puts "DFT: scan_replace + create scan ports"
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# Keep the number of scan ports stable for QoR comparisons.
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# With clock mixing enabled, all scan cells share one hash domain, so -max_chains
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# applies globally.
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set_dft_config -max_chains 1 -clock_mixing clock_mix
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# Replace functional flops with scan-capable flops.
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scan_replace
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proc dft_ensure_scan_port {port_name io_type} {
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set block [ord::get_db_block]
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set bterm [$block findBTerm $port_name]
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if { $bterm != "NULL" } {
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return
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}
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set net [$block findNet $port_name]
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if { $net == "NULL" } {
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set net [odb::dbNet_create $block $port_name]
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$net setSigType SCAN
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}
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set bterm [odb::dbBTerm_create $net $port_name]
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$bterm setSigType SCAN
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$bterm setIoType $io_type
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}
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# One-chain scan I/O + shared enable.
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dft_ensure_scan_port "scan_enable_0" INPUT
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dft_ensure_scan_port "scan_in_0" INPUT
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dft_ensure_scan_port "scan_out_0" OUTPUT
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# Functional-mode assumption for STA/power (disable scan path).
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set_case_analysis 0 [get_ports scan_enable_0]
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‎flow/scripts/dft_scan_pre_global_route.tcl‎

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# DFT scan insertion hook for ORFS.
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#
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# Intended use: set `PRE_GLOBAL_ROUTE_TCL` to this file.
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#
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# This runs after CTS, before global routing, so scan-chain connections are
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# included in routing.
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puts "DFT: execute_dft_plan (stitch scan chains)"
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# Must match `flow/scripts/dft_scan_post_floorplan.tcl`.
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set_dft_config -max_chains 1 -clock_mixing clock_mix
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# Ensure functional-mode STA/power assumptions in this stage too.
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set_case_analysis 0 [get_ports scan_enable_0]
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execute_dft_plan
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