Draft: native radio driver for meshtasticd hardware (SX126x, SX127x, SX1280, LR11x0, CH341 USB)

[A13xB0]

Native radio driver (option D in the meshtasticd plan): RepeaterTastic drives the LoRa chip on meshtasticd hardware itself, with no USB KISS modem and no meshtasticd. It's a new radio.Radio implementation, so identities, relay, plugins and MQTT don't change.

Not yet run on hardware. This PR stays a draft until testers have worked through docs/spi-radio-testing.md. Test binaries are on the spi-draft-2 prerelease.

Coverage

Chip	Buses	Example boards
SX1262, SX1268, LLCC68	spidev + GPIO, CH341 USB	MeshAdv, Waveshare, RAK6421, Nebra/Zebra, PiMesh, Femtofox, Luckfox, MeshStick, Meshtoad, uMesh
LR1110, LR1120, LR1121	spidev + GPIO, CH341 USB	Femtofox E80, PiggyStick
SX1276/SX1278 (RF95)	spidev + GPIO	Adafruit RFM9x
SX1280 (2.4 GHz)	spidev + GPIO	Module: sx1280 boards

All 61 of meshtasticd's bin/config.d/lora-*.yaml files are built in, copied unchanged under GPL-3.0 (see internal/radio/spi/boards/README.md), and all of them parse. LR2021 is left out because no meshtasticd board uses it.

What's in it

• Config: radio.driver: spi. radio.device is one of:
  • a board file path;
  • a built-in board name (MeshAdv-900M30S);
  • auto: detect a CH341 stick's product string, a Pi HAT+ EEPROM or a RAK I²C EEPROM, following meshtasticd's autoconf.
• internal/radio/spi: one radio loop (IRQ or polling, RX frames with RSSI/SNR, TX with TxDone, noise floor, channel busy) plus a driver per chip family:
  • SX126x: sync word readback, TCXO, DIO2 RF switch, errata 15.1/15.2/15.4, OCP, boosted gain;
  • SX127x: version check, PA_BOOST/DAC, errata 2.1, packet-RSSI offsets, modem-status channel busy;
  • SX1280: version string check, mantissa/exponent preamble, SF register;
  • LR11x0: two-phase SPI reads, TCXO, calibration, rfswitch_table, HP/LP/HF PA selection, bootloader detection.
• Buses, pure Go (no CGO):
  • spidev SPI_IOC_MESSAGE plus GPIO v2 chardev lines and edge events;
  • CH341 over usbfs (bit-reversed SPI stream packets, UIO pins, polled IRQ).
• Board file keys, following meshtasticd:
  • pins as numbers or {pin, gpiochip, line}, and RADIOLIB_NC;
  • Enable_Pins, SX126X_ANT_SW, DIO2_AS_RF_SWITCH, DIO3_TCXO_VOLTAGE;
  • per-chip *_MAX_POWER with meshtasticd's defaults;
  • TX_GAIN_LORA, with the same power-limit walk as RadioInterface::limitPower;
  • USB_VID/USB_PID/USB_Serialnum;
  • a repeated key resolves to its first value, as yaml-cpp does.
• kisstool: boards lists the built-in boards; --board works with info (chip diagnostics, noise floor), listen and send-text.
• Setup wizard: keeps an spi radio's board; editing a radio in the GUI no longer forces kiss.
• Tests: a fake chip model per family (configure, RX, TX), board parsing, every built-in board, autoconf mapping, EEPROM CRC, CH341 encoding.

GUI

• Modem switch in Add radio and Edit radio: USB modem | Board. The board list (GET /api/v1/boards) is grouped by host computer from each file's Meta.compatible, with /etc/meshtasticd boards first and a custom path option.
• Setup wizard: detected serial ports, Serial port by name for an unlisted one, and LoRa board on SPI or a USB stick; Test modem opens a board and shows the chip's diagnostics. Picking a board switches the driver without a restart. The relay step offers all five roles.
• Built-in board file lora-usb-xiao-sx1262-ch341.yaml for the XIAO nRF52840 + Wio-SX1262 CH341 bridge, so auto finds it.

meshtasticd's raw modem mode (PR #4) was merged in here and then removed again: it won't go upstream, and RepeaterTastic will drive meshtasticd over its client API instead (epic PR to follow).

Known gaps

• Channel busy uses preamble/header IRQs (and SX127x modem status) rather than CAD.
• LR1110 firmware updates aren't handled; a chip in its bootloader is reported.

[A13xB0]

This ships as part of the real-nodes epic, #5: epic/real-nodes is built on this branch, so please don't merge this one on its own. It will show as merged when #5 lands on main.