By name: diagnose-routing-failures description: Root-causes failed routes from a routing run's logs and the board file. Parses the JSON summary, failed-net histories, and blocking reports, correlates failures spatially with board regions and components, classifies the failure mode, and outputs a ready-to-run retry command. Use after route.py/route_diff.py runs report failed nets.
Diagnose Routing Failures
When this skill is invoked with a board file and routing log file(s), root-cause the failures and produce a targeted retry command. Routing runs should always be captured with 2>&1 | tee /tmp/<step>.txt so the logs are available.
Step 1: Parse the Structured Outputs
JSON summary
grep "JSON_SUMMARY" /tmp/route_output.txt | sed 's/.*JSON_SUMMARY: //' | python3 -m json.tool
Key fields:
failed_single: failed single-ended net namesfailed_multipoint: nets with unconnected pads, including pad coordinatesmultipoint_pads_connectedvsmultipoint_pads_total: connection success rate
Failed net histories
grep -A 30 "FAILED NET HISTORIES" /tmp/route_output.txt
Each failed net's history records its route attempts, which nets ripped it up (ripped_by, with escalation level N), and reroute outcomes. A net that was ripped and never successfully rerouted points at the net that ripped it as much as at the failed net itself.
Blocking reports
Look for blocking analysis lines:
grep -B2 -A8 -i "blocked by\|no rippable blockers\|Route stuck" /tmp/route_output.txt
These name the previously-routed nets occupying the failed route's frontier and where the search got stuck (position + layer).
Step 2: Correlate Failures Spatially
Load the board and map failures to regions and components:
from kicad_parser import parse_kicad_pcb
pcb = parse_kicad_pcb('board.kicad_pcb')
# For each failed net: where are its pads, and what is nearby?
for net in pcb.nets.values():
if net.name in failed_names:
for pad in net.pads:
print(net.name, pad.component_ref, pad.global_x, pad.global_y, pad.layers)
Check whether failures cluster:
- Near one component (especially a BGA/PGA — its auto-detected exclusion zone may be walling off paths)
- In one board region (a congested corridor every failed net needs to cross)
- On one layer (layer costs or direction preference starving that layer)
Report the spatial pattern explicitly, e.g. "all 6 failures have an endpoint within 3mm of U9's southeast corner."
Step 3: Classify and Recommend
Work through the failure modes most-targeted-first. Do not jump straight to global parameter increases — they are the last resort, not the first.
| Evidence | Failure mode | Fix |
|---|---|---|
| "no rippable blockers found" near a BGA/PGA | Blocked by the BGA exclusion zone or pre-existing copper | --no-bga-zone <ref> for that component |
| Stuck positions cluster in one corridor; blockers are routed nets that themselves had few alternatives | Corridor congestion | Suggest the user draw a guide corridor: a polyline on User.1 through a less congested region, then re-route the failed nets with --guide-corridor. Describe in words where the corridor should go (e.g. "south of J3, between the mounting hole and C14"). Do not draw the geometry yourself — guide drawing is the user's decision |
| Failed nets have source and target stubs on conflicting layers; rip-up histories show repeated mutual ripping | Same-layer crossing conflicts | --mps-layer-swap, or revisit --layer-costs |
| "Re-route FAILED: no path found" for ripped nets | Retry budget exhausted | Increase --max-iterations (e.g. 1000000) |
| Many multipoint pads failed on the same fine-pitch component | Grid too coarse for the pad geometry | --grid-step 0.05, and check --track-width/--clearance against the pad pitch |
| Failures spread across the board, blockers vary | Genuine capacity problem | Escalate in order: --max-ripup 10 → reduce --clearance/--track-width toward fab minimums → add routing layers |
Step 4: Output the Retry Command
Produce one command that retries only the failed nets with the targeted fixes, and explain each parameter change in one line:
python3 -X utf8 route.py board_routed.kicad_pcb board_retry.kicad_pcb \
--nets "SDA" "Net-(U1-Pad8)" \
--no-bga-zone U9 \
--max-ripup 10 \
2>&1 | tee /tmp/route_retry.txt
Routing only the failed nets preserves the successful routes (already in the input file) and is much faster than a full re-run. After the retry, re-check with check_connected.py, and if nets still fail, repeat the diagnosis on the new log — the failure mode often changes after the first fix.