KiCadRoutingTools: Skill for Claude Code

Identify Differential Pairs

When this skill is invoked with a KiCad PCB file, find all differential pairs — including ones name-based detection misses — and recommend routing parameters per interface.

Step 1: Baseline Name-Based Detection

python3 py_router/list_nets.py path/to/file.kicad_pcb --diff-pairs

This catches pairs following P/N naming conventions. Record the result as the baseline.

route_diff.py finds pairs with the same name matcher (net_queries.extract_diff_pair_base: _P/_N, P/N, _P0/_N0, +/-, DP/DM/DN, DPLUS/DMINUS, DDR _t/_c) and selects pairs only through it, so this baseline is the set it can route (list_nets also drops a P/N-named pair on a two-terminal crystal, #145). Naming the two nets of a pair whose names fit none of these conventions routes nothing as a pair ("No differential pairs found matching the patterns").

Step 2: Datasheet-Based Detection by Pin Function

For each IC likely to have differential interfaces (footprint/value keywords: FPGA, PHY, SERDES, USB, ETH, HDMI, LVDS, MIPI, SATA, PCIE, DDR, transceiver, redriver):

1. Check pad metadata first — KiCad symbols often carry it:

import sys
sys.path.insert(0, "py_router")
from kicad_parser import parse_kicad_pcb
pcb = parse_kicad_pcb('path/to/file.kicad_pcb')
fp = pcb.footprints['U3']
for pad in fp.pads:
    print(pad.pad_number, pad.pinfunction, pad.net_name)

Differential pin functions usually pair as ..._P/..._N, TX+/TX-, D+/D-.

1. Where pinfunction is missing or generic, WebSearch the part's datasheet pinout and map differential pin pairs to pad numbers, then to nets via the pads.

2. Trace through series passives: if a differential pin connects to a 2-pad R/C/L, follow to the net on the component's other pad — the pair often gets its "real" net name on the far side of AC coupling caps or series resistors.

A pair is confirmed when both nets trace back to a documented differential pin pair. Nets that look paired only by name or topology are suspected — list them separately for the user to confirm.