Tie decoupling and I2C checks to pintable pin names, not mux tables.

Ignore enable straps on a power rail, NC nets, and SPI aliases; treat FB as an inductor and RN as a resistor so pull-ups and beads classify correctly.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/pinscopex/graph.py

@@ -31,8 +31,10 @@ from backend.pinscopex.resolve_passives import SkippedItem, resolve_bom, resolve
 
 _PREFIX_TYPE: dict[str, ComponentType] = {
     "R": ComponentType.RESISTOR,
+    "RN": ComponentType.RESISTOR,
     "C": ComponentType.CAPACITOR,
     "L": ComponentType.INDUCTOR,
+    "FB": ComponentType.INDUCTOR,
     "U": ComponentType.IC,
     "IC": ComponentType.IC,
     "J": ComponentType.CONNECTOR,

backend/pinscopex/passive_rail_check.py

@@ -1,7 +1,8 @@
 """Deterministic supply decoupling and I2C/reset pull-up checks.
 
-These only fire when the graph already shows a power pin, an I2C net, or a
+These only fire when the graph already shows a pintable supply pin, an I2C
-reset pin — they do not guess capacitor values or datasheet µF minima.
+net/pin name, or a reset pin — they do not guess capacitor values, mux
+alt-functions, or datasheet µF minima.
 """
 
 from __future__ import annotations
@@ -22,15 +23,21 @@ _SUPPLY_PIN_RE = re.compile(
     r"VIN|VBAT|VBUS|VCORE)(?:$|[_/\d])",
     re.IGNORECASE,
 )
+_RAIL_PIN_RE = re.compile(r"^(?:\+?\d+V\d*)$", re.IGNORECASE)
 _NOT_SUPPLY_RE = re.compile(
     r"\b(VSS|GND|VEE|VOUT|VREF|SW|LX|FB|BOOT|NC|VPP)\b",
     re.IGNORECASE,
 )
-_I2C_RE = re.compile(r"\b(SDA|SCL)(\d+)?\b", re.IGNORECASE)
+_I2C_RE = re.compile(r"(?:^|[^A-Za-z0-9])(SDA|SCL)(\d+)?(?:$|[^A-Za-z0-9])", re.IGNORECASE)
+_SPI_NAME_RE = re.compile(r"(?i)\b(MISO|MOSI|SCLK|SCK)\b")
 _RESET_RE = re.compile(
     r"\b(N?RST(?:N|B)?|NRST|RESET(?:_?N|_?B)?|NRESET|CHIP_PU)\b",
     re.IGNORECASE,
 )
+_NC_NET_RE = re.compile(
+    r"^(?:n/?c|n\.c\.|nc|unconnected|no[_-]?connect|not[_-]?connected)$",
+    re.IGNORECASE,
+)
 
 
 def check_supply_decoupling(
@@ -47,6 +54,8 @@ def check_supply_decoupling(
         for pin_num, net_name in sorted(comp.pins.items(), key=lambda x: str(x[0])):
             if net_name in seen_nets:
                 continue
+            if _is_nc_net(net_name):
+                continue
             if not _is_ic_supply_pin(graph, cons, pin_num, net_name):
                 continue
             seen_nets.add(net_name)
@@ -93,6 +102,8 @@ def check_i2c_pullups(
         for pin_num, net_name in sorted(comp.pins.items(), key=lambda x: str(x[0])):
             if net_name in seen_nets:
                 continue
+            if _is_nc_net(net_name):
+                continue
             if not _is_i2c_pin(graph, cons, pin_num, net_name):
                 continue
             seen_nets.add(net_name)
@@ -140,6 +151,8 @@ def check_reset_pullups(
         for pin_num, net_name in sorted(comp.pins.items(), key=lambda x: str(x[0])):
             if net_name in seen_nets:
                 continue
+            if _is_nc_net(net_name):
+                continue
             if not _is_reset_pin(graph, cons, pin_num, net_name):
                 continue
             seen_nets.add(net_name)
@@ -183,17 +196,27 @@ def _pin_label(cons: ComponentConstraints | None, pin_num: str, net_name: str) -
     return str(pin_num)
 
 
-def _pin_blob(
+def _is_nc_net(name: str) -> bool:
-    cons: ComponentConstraints | None, pin_num: str, net_name: str,
+    return bool(_NC_NET_RE.match((name or "").strip()))
-) -> str:
+
-    parts = [net_name or ""]
+
-    if cons:
+def _pin_name_tokens(cons: ComponentConstraints | None, pin_num: str) -> list[str]:
+    """Slash-separated pin *name* tokens only — not the mux alt-function table."""
+    if not cons:
+        return []
     pin = cons.pin_by_number(pin_num)
-        if pin:
+    if not pin or not pin.name:
-            parts.append(pin.name or "")
+        return []
-            if pin.functions:
+    return [t.strip() for t in re.split(r"[/,]", pin.name) if t.strip()]
-                parts.extend(pin.functions)
+
-    return " ".join(parts)
+
+def _looks_like_supply(text: str) -> bool:
+    t = (text or "").strip()
+    if not t:
+        return False
+    if _NOT_SUPPLY_RE.search(t) and not _SUPPLY_PIN_RE.search(t):
+        return False
+    return bool(_SUPPLY_PIN_RE.search(t) or _RAIL_PIN_RE.match(t))
 
 
 def _is_ic_supply_pin(
@@ -202,10 +225,11 @@ def _is_ic_supply_pin(
     pin_num: str,
     net_name: str,
 ) -> bool:
-    blob = _pin_blob(cons, pin_num, net_name)
+    tokens = _pin_name_tokens(cons, pin_num)
-    if _NOT_SUPPLY_RE.search(blob) and not _SUPPLY_PIN_RE.search(blob):
+    if tokens:
-        return False
+        return any(_looks_like_supply(t) for t in tokens)
-    if _SUPPLY_PIN_RE.search(blob):
+    # No pintable row: fall back to net name / POWER type.
+    if _looks_like_supply(net_name or ""):
         return True
     net = graph.nets.get(net_name)
     return bool(net and net.net_type == NetType.POWER)
@@ -222,18 +246,12 @@ def _is_i2c_pin(
         r"(?i)\bSPI[_-]?(CLK|SCK|MOSI|MISO|CS|SS)\b", net,
     ):
         return False
-    primary = ""
+    tokens = _pin_name_tokens(cons, pin_num)
-    if cons:
+    if any(_SPI_NAME_RE.search(t) for t in tokens):
-        pin = cons.pin_by_number(pin_num)
-        if pin and pin.name:
-            primary = pin.name.split("/")[0].strip()
-    if re.search(r"(?i)\b(MISO|MOSI|SCLK|SCK)\b", primary):
         return False
     if _I2C_RE.search(net):
         return True
-    if _I2C_RE.search(primary):
+    return any(_I2C_RE.search(t) for t in tokens)
-        return True
-    return False
 
 
 def _is_reset_pin(
@@ -242,7 +260,9 @@ def _is_reset_pin(
     pin_num: str,
     net_name: str,
 ) -> bool:
-    return bool(_RESET_RE.search(_pin_blob(cons, pin_num, net_name)))
+    if _RESET_RE.search(net_name or ""):
+        return True
+    return any(_RESET_RE.search(t) for t in _pin_name_tokens(cons, pin_num))
 
 
 def _is_ground_net(graph: DesignGraph, name: str) -> bool:

frontend/src/lib/types.ts

@@ -13,7 +13,7 @@ export interface Finding {
   status: FindingStatus;
   recommendation?: string;
   reference: string;
-  source?: string | null; // "pin_mux_check"/"led_current_check" = deterministic; null/"review" = LLM
+  source?: string | null; // pin_mux_check / led_current_check / supply_decoupling_check / i2c_pullup_check / reset_pullup_check = deterministic; null/"review" = LLM
 }
 
 export interface FindingComment {

tests/test_passive_rail_check.py

@@ -199,3 +199,58 @@ def test_reset_floating_is_warning():
     assert len(findings) == 1
     assert findings[0].source == "reset_pullup_check"
     assert findings[0].status == "WARNING"
+
+
+def test_enable_strapped_to_rail_is_not_decoupling():
+    cons = {
+        "UTEST": ComponentConstraints(
+            mpn="UTEST",
+            pintable=[
+                Pin(number=1, name="EN"),
+                Pin(number=2, name="GND"),
+            ],
+            absolute_maximum_ratings=[], rules=[],
+        )
+    }
+    g = _graph(
+        {"U1": _ic("U1", {"1": "3V3", "2": "GND"})},
+        {
+            "3V3": (NetType.POWER, [("U1", "1")]),
+            "GND": (NetType.GROUND, [("U1", "2")]),
+        },
+    )
+    assert check_supply_decoupling(g, cons) == []
+
+
+def test_i2c_from_slash_alias_in_pin_name():
+    cons = {
+        "UTEST": ComponentConstraints(
+            mpn="UTEST",
+            pintable=[Pin(number=12, name="GPIO12/I2C1_SDA")],
+            absolute_maximum_ratings=[], rules=[],
+        )
+    }
+    g = _graph(
+        {"U1": _ic("U1", {"12": "NET-U1-12"})},
+        {"NET-U1-12": (NetType.SIGNAL, [("U1", "12")])},
+    )
+    findings = check_i2c_pullups(g, cons)
+    assert len(findings) == 1
+    assert findings[0].source == "i2c_pullup_check"
+
+
+def test_nc_supply_net_is_skipped():
+    g = _graph(
+        {"U1": _ic("U1", {"1": "NC"})},
+        {"NC": (NetType.POWER, [("U1", "1")])},
+    )
+    assert check_supply_decoupling(g, _cmap_vdd()) == []
+
+
+def test_fb_and_rn_prefixes():
+    from backend.pinscopex.graph import _classify_component
+    from backend.pinscopex.models import ComponentType
+
+    assert _classify_component("FB1", "") == ComponentType.INDUCTOR
+    assert _classify_component("RN4", "") == ComponentType.RESISTOR
+    assert _classify_component("F1", "") == ComponentType.FUSE