Port: PNut-Term-TS P81svj44 only.
Pin constants: pin-map.md, src/usb_pins.spin2.

One-time physical setup so software can run dogfood (on-chip host↔device) and later Serial Host (real MSC) without rewiring data lines.

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Safety

1. Common GND between all P2 USB pairs under test and any external hub/SSD.
2. VBUS: only Serial Host EN pins (33/37) drive port power. Never back-drive 5 V into a pair that is only D±.
3. Dogfood proto gang has no VBUS — pure D± loop for emulators.
4. Do not short Serial Host D± (34/35 or 38/39) to proto 40/41/48/49 unless you intend one electrical bus.
5. Leave PropPlug / debug pins alone.

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Topology A — Dogfood (default bring-up)

Used by harness/top_selftest.spin2 and ticket 3005.

Role	Pair (DM/DP)	EN
Host	40 / 41	none
Device min	48 / 49	none

Jumpers (required):

Wire	From	To
D−	40	48
D+	41	49

   P2
 40 ──D−── 48     host cog = 40/41
 41 ──D+── 49     device cog = 48/49

Software: dev.start(48) then app.open(40, -1).

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Topology B — Serial Host real media (MSC later)

Priority	Logical	DM/DP	VBUS EN
1st	Ch1 (prefer top USB-A)	34/35	33 high
2nd	Ch2 fallback	38/39	37 high

• Plug Serial Host addon on base 32.
• Supply 5 V to the addon (Eval ACC/5V shunt as needed).
• USB SSD/thumb in top socket first; software may fall back to ch2.
• No requirement to gang proto pairs for MSC path.

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Topology C — Hub (multi-device, later)

1. Host pair = Serial Host ch1 (34/35) + EN 33.
2. Hub upstream → that USB-A; hub powered externally.
3. Downstream: real SSD and/or future emulator ports (only if you jumper extra pairs to hub-facing connectors — not the default proto gang).
4. Software: same host object; addresses from enum (ticket 1090/1100).

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Pin picture

Serial Host (base 32)                 Proto dogfood gang
┌──────────────────────┐              40 ── D− ── 48
│ 32 LED1              │              41 ── D+ ── 49
│ 33 EN1 → VBUS ch1    │
│ 34 D−  → USB ch1     │              independent of Serial Host
│ 35 D+  → USB ch1     │
│ 36 LED2              │
│ 37 EN2 → VBUS ch2    │
│ 38 D−  → USB ch2     │
│ 39 D+  → USB ch2     │
└──────────────────────┘
         ▲
    real SSD / stick

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SE0 / float notes (multi pair)

• Only one host driver on a bus. Device pairs idle Y=0 (float) with device-mode pull-up.
• Dual smart-pin pairs on one gang both receive; host drives, device listens then drives handshakes.
• Long SE0 is host bus reset (≥10 ms). Devices must not treat EOP SE0 as reset (use multi-ms hold).

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Acceptance (0110)

• [x] Human can wire dogfood from this doc alone
  
• [x] Serial Host map + VBUS rules
  
• [x] Hub sketch for later
  
• Harness references this path for non-MSC tests