CM5 Carrier Port — Status & Handoff

Handoff doc for whoever (human or LLM) continues this work. Read this first, then .claude/skills/kicad-port/SKILL.md (the mandatory workflow/verify-loop), then CM5_Carrier_Design.md (frozen rev-A spec).

What this repo is

Two intertwined goals:

Improve Claude's EDA tooling — the kicad-happy skill suite (kicad, datasheets, spice, …), wired in as Claude Code skills via ~/.claude/skills/{kicad,datasheets,spice} -> kicad-happy/skills/* symlinks. The toolkit clones (kicad-happy/, kicad-claude-toolkit/, MCP-KiCad/) are gitignored — re-clone if missing.
Port the Raspberry Pi CM5IO reference into a custom CM5 carrier board — the real test bed (PTP/timing instrumentation node: 15V→5V front end, GbE magjack, M.2 E-key Wi-Fi (AW7915/MT7915), 2×USB-A, USB-C programming, RTC, GPS-PPS distribution).

Method is diff-from-reference: refs/ holds the untouched CM5IO reference; carrier/ is the working copy. Every edit is verified against analysis/baseline/cm5io.json.

Environment / tooling state (macOS, Homebrew)

kicad-cli ✅ (/opt/homebrew/bin/kicad-cli) — ERC + netlist export
poppler ✅ (pdftotext) — datasheet page selection
ngspice ✅ — spice skill; full verify loop validated on the reference (8 subcircuits pass)
Python ≥3.10 (Homebrew 3.14)

The verify loop (run after EVERY schematic edit)

SCH=carrier/CM5IO.kicad_sch ; KSCR=~/.claude/skills/kicad/scripts
kicad-cli sch erc --exit-code-violations --format json -o /tmp/erc.json "$SCH"   # hard gate
python3 $KSCR/analyze_schematic.py "$SCH" -o /tmp/head.json                       # structural
python3 $KSCR/diff_analysis.py analysis/baseline/cm5io.json /tmp/head.json --text # vs baseline

Track the ERC DELTA, not the absolute — the reference already has 182 pre-existing violations (mostly unconnected_wire_endpoint). A good edit introduces zero new types.
The analyzer diff is the semantic gate (names broken design intent); ERC is the hygiene gate.
For kept-block integrity, also diff kicad-cli sch export netlist before/after — it caught a mis-inventoried part (see R8 below).

Datasheet extraction (done)

CM5 module extracted to datasheets/extracted/SC1466_43a9ec.json (200 pins, score 8.7/10, queryable via ~/.claude/skills/datasheets/scripts/datasheet_features.py). Drove the NC pin lists for every strip (e.g. HDMI Module1 pins = all pins whose datasheet name starts HDMI).

The strip tool: `tools/retire_block.py`

General block-retirement for these s-expr sheets. Capabilities:

excise symbols by Reference; retire nets by name-glob (all label types: local / hierarchical / global)
anchor-aware wire removal (union-find): removes a wire only if its connected component reaches no kept anchor (kept non-power pin or kept label) AND is seeded by this edit — so shared nets survive and pre-existing dangles are untouched
place (no_connect) on exposed Module1 pins (pin coords via a validated transform abs=(px+rot(lx,ly).x, py-rot(lx,ly).y), rot0/no-mirror; refuses other orientations)
clean orphaned power flags, dangling NCs, orphaned labels
--sheet-ports NAME,... removes root-sheet hierarchical pins + connecting wires

Usage: python3 tools/retire_block.py <sheet> --symbols J7,U18 --nets 'SD_*' --nc-pins 57,61 [--sheet-ports ...] [--apply] (dry-run without --apply).

Known gap (next improvement): does NOT auto-prune orphaned power-label/wire stubs left after a connector is removed (e.g. leftover +3.3v/HDMI_5v labels). Those were cleaned manually — see git history.

Strip phase — DONE (microSD + HDMI + MIPI), ERC 182 → 136, 0 new violations, 0 regressions

Block	Sheet(s)	Command(s) (run with `--apply`)
microSD	CM5_GPIO	`--symbols J7,U18,C5 --nets 'SD_*' --nc-pins 57,61,62,63,67,69,75`
HDMI	CM5_HighSpeed	`--symbols J22,J10 --nets 'HDMI0_,HDMI1_,HDMI_5v' --nc-pins 143,145,146,147,148,149,151,152,153,154,158,160,164,166,170,172,176,178,182,184,188,190,199,200`
MIPI/camera	CM5_HighSpeed, CM5_GPIO, CM5IO(root)	(1) HighSpeed `--symbols J5,J16 --nets 'DPHY0_,DPHY1_,SCL1,SDA1' --nc-pins 115,117,121,123,127,129,133,135,139,141,175,177,181,183,187,189,193,194,195,196` (2) GPIO `--nc-pins 80,82,97,100` (3) root `--sheet-ports SCL0,SDA0,CAM_GPIO0,CAM_GPIO1` (4) HighSpeed `--symbols R8 --nets 'SCL0,SDA0'` (5) manual: remove 3 orphaned +3.3v labels + 2 wire stubs

Notes that bit us (don't re-learn the hard way):

MIPI lanes are labeled DPHY0_*/DPHY1_*, NOT MIPI*. The connectors J5/J16 are camera FFCs bundling DPHY + cross-sheet I2C0 (SCL0/SDA0) + CAM_GPIO0/1 — a 3-sheet hierarchical block.
R8 is a camera pull-up, not USB (the Explore-agent inventory was wrong). Confirmed via kicad-cli sch export netlist (R8.2 → J16.17). Always verify inventory against the netlist.
SCL0/SDA0 (I2C0) are camera-only 2-node nets (netlist-proven). NC'd to reserve I2C0 for a future external I2C RTC (CM5's own RTC is on-module via VBAT). If you add an external RTC, wire it here.

Next steps

Drop the PCIe-M2 sheet entirely (NVMe M-key — not used; the M.2 E-key Wi-Fi will be a FRESH sheet in the add phase, per design decision). Use --sheet-ports for its root hierarchical pins.
Re-baseline: capture a new analyzer baseline of carrier/ so the add phase diffs against the stripped design, not the original reference.
Add phase: 15V→5V buck front-end (reverse-protection + TVS), M.2 E-key (PCIe Gen2 ×1 + CLKREQ/PERST/RF_KILL + 3.3V), GPS connector, PPS distribution (GPS PPS → TVS → Schmitt buffer → fan-out: CM5 Ethernet_SYNC_OUT + 2 header taps). SPICE-validate the buck divider + PPS network.

Out-of-repo notes

Richer running notes live in this machine's Claude memory: ~/.claude/projects/-Users-noise-Documents-obsidian-rpiboard/memory/ (project-cm5-eda, port-progress, eda-tooling-gaps, tooling-installs-cm5). This doc is the portable subset.

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