OpenPuck RF Sniffer

A passive 2.4 GHz sniffer for the link between a real Valve SC2 puck and its controller. It never transmits, so it cannot disturb the pairing — it only listens, and streams every frame to a browser app in real time with Start Cap / End Cap.

Use it to capture the actual puck↔controller traffic for any function (shutdown, LED, battery, …), isolate the relevant frames, and export them.

What you need

A second nRF52840 board (e.g. the same Pro Micro / Feather you flash OpenPuck onto) — not the puck.
The real Valve puck + controller, paired and working.
Chrome or Edge (WebUSB).

1. Flash the sniffer firmware

arduino-cli compile -b adafruit:nrf52:feather52840 \
  --build-property "build.extra_flags=-DNRF52840_XXAA {build.flags.usb}" \
  --upload -p <PORT> puck_sniffer

(Same manual-DFU/double-tap-reset dance as OpenPuck if the port won't auto-reset.) It enumerates as 28DE:534E "OpenPuck Sniffer".

2. Open the app

WebUSB needs a secure context, so not a file:// path. Either:

Hosted: https://safijari.github.io/OpenPuck/sniffer.html (once docs/ is pushed to gh-pages), or
Local: cd docs && python3 -m http.server → open http://localhost:8000/sniffer.html

Click Connect sniffer, pick OpenPuck Sniffer.

3. Capture

The link is Nordic Gazell: the on-air address is a System Address random per session (not derived from the bond), and the active E3-poll / F1-reply exchange rides a small channel set {primary, 2, 80} derived from that address. The puck's ~5 Hz E1/E2 keepalive trickles in even when the controller isn't being actively polled — so seeing only E2 and C→P: 0 means the controller isn't in an active session yet.

Recipe (mirrors ~/nrf-sniffer/capture_puck_session.py):

Status shows ACQUIRE → it catches the puck's E1 on ch2 and locks the session address.
It then hunts the channel set for the controller's 0xF_ replies. Make the session active: with the controller connected, do heavy trackpad / move sticks so the puck polls fast. Watch C→P climb — that means it parked on the live channel. (Bonded reconnect uses a fresh address → if it won't lock, power-cycle the controller during ACQUIRE so the new E1 is heard.)
With C→P climbing, ● Start Cap, trigger the action in Steam (turn off / LED / let battery move), ■ End Cap, Download. Send me the file.

Direction: P→C (opcode 0xE_, puck→controller — LED/shutoff commands ride here) vs C→P (0xF_, controller→puck — battery/telemetry rides here). The filter box matches payload hex (e.g. 9f).

Bond info (which controller/slot, its serial + uuids) is read over USB, not the air — scmd/pairtui.py in ~/nrf-sniffer. Useful for labelling a capture; it does not give the on-air address (random per session).

How it works

After RX the radio buffer is [LENGTH][S1][payload…]; payload[0] is the opcode. The puck advertises its per-session base/prefix/channel inside the E1 host frame on the shared ibex/ch2 rendezvous, so the sniffer reads those, retunes to the session, and receives both directions (same ESB base — and it now listens on all 8 ESB pipes of that base, so a controller reply on a different prefix is still caught; the pipe column / status last pipe shows which RXMATCH each frame hit). A QoS channel-hop is followed via the E1 keepalive. When the session goes silent it sweeps clean candidate channels keeping the learned address (rather than abandoning to ch2) and only falls back to a full discovery scan after two dry sweeps. Radio parameters are OpenPuck's CRC-validated config (radio.cpp).

If you only see `E2`/`E1` on ch2 and never the controller's `0xF_` replies

That means it never camps on the session. Read a real E1 row in the table (a P→C, op e1 frame): its payload bytes are e1 [proteus:4] [ibex:4] [CH] 00 00 00 [BASE:4] [PFX] — i.e. byte 9 = session channel, bytes 13–16 = session base, byte 17 = prefix (the "E1 advertises" stat shows the sniffer's own read of these). Cross-check that against where traffic actually is, then type the six values into pin session (b0 b1 b2 b3 pfx ch, address bytes hex) and click Pin to force the sniffer onto that exact session — this bypasses auto-acquire entirely, which is the reliable path if the real puck's E1 offsets differ from ours.

Stream protocol (WebUSB bulk)

packet: C0 DE [N] [t_us:4 LE] [ch] [flags] [rssi] [match] [N raw bytes] (flags bit0 = CRC ok; match = RXMATCH pipe; raw = [LEN][S1][payload])
status: C1 DE [state] [curCh] [base:4] [prefix] [cap] [hb:2] [advCh] [advBase:4] [advPfx] [lastMatch] (19 B; adv* = session parsed from the last E1)
commands (bulk OUT): 01 start · 02 stop · 03 re-acquire · 04 <ch> pin channel · 05 <b0 b1 b2 b3 pfx ch> pin full session

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