feat: Add NiceRF LoRa2021 (LR2021 Gen 4) variant support

[c03rad0r]

Summary

Adds MeshCore support for the NiceRF LoRa2021 module (Semtech LR2021 Gen 4) on ESP32-C3_Mini_V1 development board.

Hardware

Component	Details
MCU	ESP32-C3_Mini_V1 (Maker go, 22.52x18mm, USB-C, 4MB flash)
Radio	NiceRF LoRa2021 (Semtech LR2021 Gen 4, 19.72x15mm, 18-pin)
Antenna	Wire dipole (~8.2cm for 868 MHz Sub-GHz)
Cost	~$8 total (MCU + radio module)
Frequency	Sub-GHz: 150-960 MHz + 2.4 GHz (dual-band)

RadioLib Class

Uses the LR2021 class (extends LRxxxx → PhysicalLayer). This is a separate RadioLib class from LR1121 (which extends LR11x0). RadioLib v7.6.0 (already in MeshCore deps) includes LR2021 support.

Key differences from SX1262:

• IRQ on DIO9 (not DIO1) — set via irqDioNum = 9 + setDioFunction(9)
• setRxBoostedGainMode(uint8_t level) takes 0-7, not bool
• No DIO2-as-RF-switch (NiceRF handles internally)
• Crystal oscillator (XTAL), not TCXO — tcxoVoltage = 0
• getPacketLength() override handles header errors (same as LR1110 pattern)

Known Issue: Arduino SPI

The Arduino SPIClass on ESP32-C3_Mini_V1 returns all-zero SPI responses, causing RADIOLIB_ERR_SPI_CMD_FAILED (-707). The same hardware works with ESP-IDF's spi_bus_initialize().

This variant includes EspIdfHal.h — a custom RadioLib HAL that bypasses Arduino SPIClass and uses ESP-IDF's spi_bus_initialize() / spi_device_polling_transmit() directly. This is the same approach used in our ESP-IDF tracker firmware.

Root cause hypothesis: The ESP32-C3 has one SPI peripheral (FSPI/SPI2_HOST). The Arduino SPIClass may not properly reconfigure FSPI when the SPI pins differ from the default boot-time configuration (our board uses GPIO2/6/7 instead of default SPI pins).

If anyone has insight into why Arduino SPI fails on this board, I would love to fix this properly and remove the custom HAL.

Build Targets

All verified building against dev branch:

Target	Flash	RAM	Status
LR2021_companion_radio_usb	542 KB (41%)	140 KB (43%)	✅
LR2021_repeater	—	—	✅
LR2021_room_server	—	—	✅
LR2021_secure_chat	—	—	✅
LR2021_kiss_modem	—	—	✅

All fit within ESP32-C3 4MB flash. Reference build (Heltec_v3_companion_radio_ble) passes — no regressions.

Files Added

Radio Helpers (in src/helpers/radiolib/)

• CustomLR2021.h — Extends LR2021, adds std_init(), isReceiving(), getPacketLength() override
• CustomLR2021Wrapper.h — Extends RadioLibWrapper, implements setParams(), doResetAGC(), getSpreadingFactor()

Board Variant (in variants/nicerf_lr2021/)

• platformio.ini — 5 build environments with LR2021 pin mapping
• target.h / target.cpp — Radio init via EspIdfHal
• NiceRFLR2021Board.h — Board class (deep sleep, battery ADC)
• EspIdfHal.h — ESP-IDF SPI HAL (documented workaround)

Board Definition (shared)

• boards/esp32c3_supermini.json — ESP32-C3 SuperMini V1 board definition
• variants/esp32c3_supermini/pins_arduino.h — Pin mapping (D0-D10 = GPIO0-GPIO10)

Testing

• All build targets compile on dev branch
• No regressions on reference builds
• Flash to ESP32-C3_Mini_V1 + NiceRF LoRa2021 hardware
• Radio init succeeds
• Noise floor calibration: -102 dBm stable
• Companion connects via meshcore-cli v1.5.7
• Advert TX verified
• Two-device encrypted chat (second board in progress)
• Community node reception test (Berlin, no nearby nodes found indoors)

Related

• Related to [Feature request] LilyGo T-Watch S3 + T3S3 (LR1121 / SX1280) board support + a 2.4 GHz LoRa frequency plan #2678 — LR2021 also supports 2.4 GHz LoRa (future work)
• Related to [Suggestion] [repater] Support multiple radios, to build backhauls or bridges. #2441 — LR2021 is dual-band (Sub-GHz + 2.4 GHz), relevant to multi-radio
• Note: LR2021 is a different RadioLib class from LR1121 (PRs Lilygo T3S3 LR1121 Variant Support #2696, Add MuziWorks Base Duo board support (nRF52840 + LR1121) 🤖🤖 #2198) — not conflicting

Pin Mapping

ESP32-C3_Mini_V1  →  NiceRF LoRa2021
3V3               →  Pin 1 (VCC)
GND               →  Pin 2,8,11,12,18
D2 (GPIO2)        →  Pin 3 (MISO)
D7 (GPIO7)        →  Pin 4 (MOSI)
D6 (GPIO6)        →  Pin 5 (SCK)
D10 (GPIO10)      →  Pin 6 (NSS/CS)
D4 (GPIO4)        →  Pin 7 (BUSY)
D3 (GPIO3)        →  Pin 14 (RST)
D5 (GPIO5)        →  Pin 15 (DIO9/IRQ)