LoRa (Rust + Embassy on RP2040/RP2350)

A Rust workspace that implements a no_std, async SX1278 LoRa driver and a set of example applications for Raspberry Pi Pico-class boards:

• radio-sender (RP2350/Pico 2): transmits a short message repeatedly
• radio-listener (RP2040/Pico): receives packets and logs RSSI/SNR
• lora-driver: embedded-hal 1.0 async driver for the SX1278
• led (RP2350): simple LED blink
• usb (RP2350): USB logger + LED blink skeleton

The examples are built on Embassy and target the RP2040 and RP2350 using their respective Arm Cortex-M cores.

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Hardware

• Boards: Raspberry Pi Pico (RP2040) and/or Raspberry Pi Pico 2 (RP2350)
• Radio: SX1278 LoRa module (433 MHz), 3.3 V logic and power
• Wiring (SPI0 on Pico header):
  • SCK → GP2
  • MOSI → GP3
  • MISO → GP4
  • NSS/CS → GP5
  • RESET → GP6
  • LED (on-board) → GP25
  • Power: 3V3 and GND
• Antenna: Use a proper 433 MHz antenna for the SX1278 module

The examples use these LoRa settings by default:

• Frequency: 433_000_000 Hz
• Bandwidth: 125 kHz
• Spreading factor: SF12
• Coding rate: 4/8
• Sync word: 0x12
• TX power: up to 20 dBm with PA_BOOST

Note: DIO0/IRQ is not used in these examples; RX/TX completion is polled.

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Repo Layout

• Workspace root Cargo.toml lists members:
  • radio-sender/ (RP2350, target thumbv8m.main-none-eabihf)
  • radio-listener/ (RP2040, target thumbv6m-none-eabi)
  • led/ (RP2350)
  • usb/ (RP2350)
  • lora-driver/ (platform-agnostic, no_std)
• Each runtime crate has:
  • .cargo/config.toml with its target triple and a PowerShell runner
  • memory.x and build.rs for linker configuration

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Prerequisites

• Rust (stable) via rustup
• Arm embedded targets:

  rustup target add thumbv6m-none-eabi thumbv8m.main-none-eabihf

• UF2 tooling (used by provided PowerShell scripts):

  cargo install elf2flash

• Windows (recommended for the provided runner scripts). On Linux/macOS, adapt the copy step or the runner command.

The crate-level .cargo/config.toml files set runner to a PowerShell script that:

1. converts the built ELF to a UF2 file with elf2flash, and
2. copies it to the UF2 mass-storage device exposed by the board.

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Flashing & Running

General flow (per example crate):

1. Put the board in bootloader (UF2) mode: hold the BOOTSEL button while plugging in USB, or press RESET with BOOTSEL held.
2. A removable drive named like RPI-RP2, RPI-RP2350, or PICO appears.
3. From the example crate directory, run cargo run --release.

The configured runner will convert the artifact to UF2 and copy it to the detected drive (defaults to E:\, otherwise auto-detects a removable RPI* volume).

Radio Sender (RP2350 / Pico 2)

cd radio-sender
cargo run --release

• SPI pins: GP2/GP3/GP4, CS: GP5, RESET: GP6
• Periodically sends: "Hello from Pico 2 - <counter>"
• LED blinks briefly while sending

Radio Listener (RP2040 / Pico)

cd radio-listener
cargo run --release

• Same SPI/CS/RESET pins as the sender
• Logs received payloads plus RSSI/SNR; automatically re-arms or resets the radio on CRC errors/timeouts

LED Blink (RP2350)

cd led
cargo run --release

USB Logger + Blink (RP2350)

cd usb
cargo run --release

• Exposes a USB CDC serial interface and logs via embassy-usb-logger
• Connect with any serial terminal (baud setting is typically ignored for USB CDC; 115200 8N1 is fine)

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Development Notes

• Driver crate: lora-driver/ is a no_std async driver for the SX1278 using embedded-hal and embedded-hal-async traits plus embassy-time.
• Targets:
  • RP2040: thumbv6m-none-eabi
  • RP2350: thumbv8m.main-none-eabihf (Cortex-M33)
• Linker scripts: each runtime crate ships a memory.x and copies it in build.rs.
• Logging: examples use the log facade with embassy-usb-logger.

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Tuning the Radio

If you need different PHY settings, change the calls in radio-sender/src/main.rs and radio-listener/src/main.rs:

• set_frequency(u32 hz)
• set_bandwidth(Bandwidth)
• set_spreading_factor(SpreadingFactor)
• set_coding_rate(CodingRate)
• set_tx_power(level, use_pa_boost)
• set_sync_word(u8)

Ensure both ends use compatible parameters and a proper antenna for the chosen band.