по́голос (poholos, ˈpo-ho-los) — rumor, hearsay.

A peer-to-peer mesh chat, carried entirely by Bluetooth Low Energy advertising frames. No connections, no pairing, no GATT: every node scans and advertises simultaneously, and messages flood the mesh hop by hop until their TTL runs out.

Workspace layout

crates/
├── poholos                  # protocol core: packets, wire codec, seen-cache,
│                            # router, airtime rotation - no_std, zero I/O
├── poholos-cli              # tokio console app: chat loop + UDP/BLE transports
├── poholos-morse            # no_std morse-code composer: dot/dash -> text
├── poholos-microbit         # micro:bit v2 mesh-node firmware (Embassy; own
│                            # workspace, validated end-to-end on hardware)
└── poholos-microbit-morse   # micro:bit v2 morse-input node (Embassy; own
                             # workspace, validated end-to-end on hardware)

The core library never touches a socket or a radio. The router is a pure state machine (ingest(bytes) -> RouteAction), which keeps the entire protocol unit-testable and reusable from embedded targets. See crates/poholos/README.md for the core crate's own API overview.

Quick start

Two terminals on one machine (or any LAN), no Bluetooth needed:

cargo run -p poholos-cli -- --name alice --transport udp
cargo run -p poholos-cli -- --name bob   --transport udp

Real BLE radio:

cargo run -p poholos-cli -- --name alice     # BLE is the default (no need for --transport ble)

--name appends a random 4-hex-digit suffix on every start; use --id alice-0001 instead to pin the full identity (and thus the wire id) across restarts — required when something addresses you by a baked-in name, like the micro:bit's buddy telegram.

Type a short message to broadcast (hearsay). @bob-9c01 hi sends a unicast (telegram) — the wire id derives from the target's full display name, no peer directory required. /quit exits.

Received messages print with a local receive timestamp and addressing, so logs from several nodes can be correlated during testing:

2026-06-11 14:32:07 [mb-60c6 → all] SOS - test
2026-06-11 14:32:09 [mb-60c6 → you] I am OK - long status sent over BLE 5 extended advertising

Wire format (version 0, max 22 bytes)

byte 0      : ver(2 bits)=0 | has_dest(1 bit) | ttl(5 bits)
bytes 1–2   : seq, u16 BE (starts random, wraps)
bytes 3–6   : src wire id, u32 BE (fnv64 of node name, truncated)
[bytes 7–10]: dest wire id, u32 BE - present iff has_dest
rest        : payload - ≤ 15 bytes hearsay, ≤ 11 bytes telegram

• DEFAULT_TTL = 16, MAX_TTL = 31. hop() refuses at ttl <= 1, so a TTL of 0 never appears on the wire.
• Dedup key = FNV-1a 64 over (flags, src, seq, dest?, payload) — TTL excluded so the same packet at different hop counts dedups correctly.
• Manufacturer-data company id 0xF10C (above the assigned range; BlueZ silently drops 0xFFFF).
• Messages above the protocol maximum (200-byte payload) are rejected at the prompt, not fragmented; a frame a given transport cannot physically carry fails that send with a platform-specific message.

Wire version 1 (extended advertising)

Frames past the 22-byte legacy budget are tagged wire version 1 and carry up to a 200-byte payload over BLE 5 extended advertising. The header layout is identical — only the permitted length differs — and encode picks the version by size: short messages stay version 0 (heard by every node, legacy included) and only long ones become version 1 (heard by extended-scan-capable nodes). Where the radio supports it, version 1 rides the Coded (long-range, S=8) PHY — the micro:bit always, Windows when the adapter can (verified per adapter at startup; otherwise plain extended advertising) — trading ~16× the airtime for roughly 4× the range. Today Windows and the micro:bit send version 1 — Windows capped at ~156 bytes by the test adapter (the cap is PHY-independent), the micro:bit the full ~200; extended-scan-capable nodes receive it, and the UDP test transport carries it in full. See Platform notes for what's validated where.

Library features

Feature	Default	Effect
std	yes	hashlink seen-cache, Backtrace in errors
serde	no	Serialize/Deserialize on core types
postcard	no	to_postcard_slice/from_postcard (no_std-friendly)

Without std the crate is no_std: the seen-cache becomes a fixed [u64; 512] ring and the wire codec works on borrowed buffers.

Platform notes

These three platforms were validated on real radio.

OS	Scan	Advertise	Send budget
Linux	btleplug	BlueZ manufacturer data (bluer, Type::Peripheral)	22 bytes
Windows 11	btleplug	BluetoothLEAdvertisementPublisher manufacturer data	22 legacy / ~156 extended
macOS	btleplug	CoreBluetooth 128-bit service UUID (1-byte tag+len)	15 bytes

Windows cannot act as a GATT peripheral (HRESULT failure) — irrelevant here, since poholos only broadcasts. macOS can hear full 22-byte frames but can only send what fits a single 128-bit service UUID: 15 raw bytes (one byte tags and lengths the frame), so hearsay typed on a Mac is capped at 8 payload bytes and telegrams at 4.

Windows and the micro:bit are dual-stack: each sends wire version 0 as a legacy advertisement (heard by every node) and oversized wire version 1 via BLE 5 extended advertising on the Coded (long-range) PHY, and each scans with extended scanning across both primary channel sets (1M and Coded), which receives everything. Windows TX is capped ~156 bytes by the test adapter (identical cap measured on 2M and Coded); the micro:bit carries the full ~200. Linux (my test box is BLE 4.2-only) and macOS remain version-0 senders. Short messages stay version 0, so the mesh stays fully connected regardless of who speaks version 1.

Coded-PHY reception on Windows needs one line btleplug 0.12 lacked (UseCodedPhy on the WinRT watcher); the fix was upstreamed (deviceplug/btleplug#463) and ships in btleplug 0.13, which the workspace now uses.

Verifying a fresh checkout

cargo fmt --all --check
cargo clippy --workspace --all-targets
cargo test  --workspace
cargo test  -p poholos --no-default-features   # no_std ring backend

# Embedded core (rustup target add thumbv7em-none-eabihf):
cargo build -p poholos --no-default-features --target thumbv7em-none-eabihf

# micro:bit v2 firmware (own workspaces; build from inside each crate so
# its .cargo/config.toml target settings apply):
(cd crates/poholos-microbit && cargo build --release)
(cd crates/poholos-microbit-morse && cargo build --release)

The Linux, Windows, and macOS advertisers, the btleplug scanner (both frame shapes), and both micro:bit firmwares (canned and morse-input) are all validated on real radio, including a two-hop Mac → Windows → micro:bit telegram relay across encodings.

micro:bit v2 firmware

crates/poholos-microbit is an Embassy-based full mesh node for the BBC micro:bit v2 (nRF52833, thumbv7em-none-eabihf), radio via the Nordic SoftDevice Controller + trouble (linked into the image — no separate SoftDevice flash), validated end-to-end against Windows and macOS desktop nodes, including a two-hop Mac → Windows → micro:bit relay. It scans continuously with extended scanning on both the 1M and Coded primary channels (so it hears legacy, extended, and long-range coded advertisements alike), relays with the same flood/TTL/dedup semantics and rotation airtime policy as the desktops, and is dual-stack: short frames go out as legacy advertisements, oversized (wire version 1) frames via extended advertising on the Coded (long-range, S=8) PHY. Delivered messages scroll on the 5×5 LED matrix, each with a leading glyph for its kind — * for a broadcast, @ (plus a chime on the onboard speaker) for a telegram addressed to it. It originates two canned messages:

• Button A — a long "I am OK" status telegram to the preconfigured buddy node, sized to ride wire version 1 / extended advertising.
• Button B — "SOS - test" broadcast.

Known gap: the board only parses manufacturer-data advertisements, so it cannot hear macOS nodes (which advertise a service UUID) directly yet — they reach it relayed through a Linux or Windows node.

Identity is mb-xxxx, derived from the factory device id; the board scrolls its own name at boot so you can @mb-xxxx hello it. The buddy is baked in at compile time via POHOLOS_BUDDY (default alice-0001) and pairs with a desktop holding a stable identity:

cargo install probe-rs-tools         # once; flashes via the onboard probe
# once: LLVM is needed at build time (bindgen for the Nordic SDC blob);
# on Windows: winget install LLVM.LLVM, then set LIBCLANG_PATH to its bin
cd crates/poholos-microbit
cargo run --release                  # flash + stream defmt logs

# on the desktop (--id pins the suffix so the buddy address stays valid):
cargo run -p poholos-cli -- --id alice-0001

micro:bit v2 morse-code node

crates/poholos-microbit-morse is a variant firmware whose input is morse code keyed on the two buttons instead of canned messages — otherwise a full mesh node, identical on the radio: dual-stack across both wire versions like the canned firmware, so a short keyed message broadcasts as a legacy advertisement and a long one rides BLE 5 extended advertising on the long-range Coded PHY. It builds on poholos-morse, a small no_std, host-tested decoder that turns dot/dash elements plus pause boundaries into text.

Keying:

• Button A tap = dot, Button B tap = dash. The first tap begins a message; a pause auto-commits the current letter, a longer pause inserts a word space.
• Hold A = finish & send (broadcast). Hold B = clear.

Feedback on the 5×5 matrix (with a speaker sidetone per press):

• each press flashes its dot/dash glyph;
• each completed letter is flashed as a character;
• ✗ — press rejected (the letter is past the 6-element morse maximum: pause to let it commit);
• → sent, ← cleared.

The decoded text and the running dot/dash pattern also stream to the defmt log. Build and flash exactly like the canned firmware:

cd crates/poholos-microbit-morse
cargo run --release

License

Split-licensed by component:

• poholos core (crates/poholos) — dual-licensed MIT OR Apache-2.0, at your option.
• Everything else (poholos-cli, poholos-morse, poholos-microbit, poholos-microbit-morse) — AGPL-3.0-only.

See LICENSING.md for details.