sdrangel/plugins/channeltx/modmeshcore/readme.md

MeshCore modulator plugin

Introduction

This plugin codes and modulates a transmission signal based the LoRa Chirp Spread Spectrum (CSS) modulation scheme with a MeshCore payload.

MeshCore (https://github.com/meshcore-dev/MeshCore, MIT) is a mesh networking protocol distinct from Meshtastic. The two share LoRa as the PHY layer but differ at the packet layer (envelope, addressing, crypto, routing). This plugin builds and transmits MeshCore wire packets — ADVERT, TXT_MSG, ANON_REQ, GRP_TXT, ACK — using vendored crypto (Monocypher for Ed25519 + X25519, tiny-AES-c for AES-128-ECB, Qt SHA-256 + hand-rolled HMAC-SHA256).

The encode pipeline is derived from the Meshtastic modulator (LoRa-SDR-based, configurable BW/SF/CR/sync). MeshCore EU defaults are baked in: 869.618 MHz / 62.5 kHz / SF 8 / CR 4/8, sync word 0x12.

This is a companion to the MeshCore demodulator plugin (channelrx/demodmeshcore) and the standalone lora_trx headless transceiver in gr4-lora.

Status

Functional surfaces:

• TX of ADVERT / TXT_MSG / ANON_REQ / GRP_TXT / ACK / PATH / CTRL via the MESHCORE: command syntax below.
• LoRa PHY with MeshCore EU radio defaults.
• Identity store: an Ed25519 seed is persisted under the application support directory, auto-loaded by MeshcoreMod, and used to sign outgoing ADVERTs. Encoder output is bit-exact against gr4-lora's meshcore_tx.py::build_advert_raw reference for the same seed and timestamp.
• REST sendNow action (SWGMeshcoreModActions) for programmatic single-packet TX.
• Radio parameters (BW, SF, CR, preamble length, frequency offset) exposed via combo controls. BW combo includes 62500 / 125000 / 250000 Hz — the bandwidths used by the MeshCore firmware CLI's set radio freq_MHz,bw_kHz,sf,cr command.
• Preset combo populated with the well-known MeshCore regional defaults (EU_NARROW, EU_LONG_RANGE, EU_MEDIUM_RANGE, AU, AU_VICTORIA, CZ_NARROW, EU_433_LONG_RANGE, NZ, NZ_NARROW, PT_433, PT_868, CH, USA, VN, USER). Default is EU_NARROW (869.618 MHz / SF 8 / BW 62.5 kHz / CR 4/8). Selecting a preset applies its freq/BW/SF/CR via modemmeshcore::command::applyMeshcorePreset.
• The Region and Channel controls are hidden: region is implicit in the preset frequency, and MeshCore has no numbered Channel concept.

Outstanding:

• WebAPI schema reuses SWGMeshtasticModSettings as a placeholder; a dedicated SWGMeshcoreMod* schema would require regenerating the SWG bindings.

MESHCORE: command syntax

Send a MeshCore wire packet by setting the channel's "Text message" to a line starting with MESHCORE::

MESHCORE: type=advert; seed=<hex64>; name=NodeA
MESHCORE: type=txt_msg; seed=<hex64>; dest=<hex64>; text=Hello
MESHCORE: type=anon_req; seed=<hex64>; dest=<hex64>; data=<hex>
MESHCORE: type=grp_txt; channel=public; text=Hello group
MESHCORE: type=ack; dest=<hex64>; msg_hash=<hex8>

Optional radio overrides on any line: sf=8, bw=62500, cr=8 (for 4/8), sync=0x12, freq=869.618M, preamble=8.

References

• MeshCore protocol: https://github.com/meshcore-dev/MeshCore
• gr4-lora python implementation: scripts/src/lora/core/meshcore_crypto.py
• Vendored Monocypher: https://monocypher.org (BSD-2-Clause OR CC0-1.0)
• Vendored tiny-AES-c: https://github.com/kokke/tiny-AES-c (public domain)