ground-station

name	ground-station
description	Ground station subproject context. Use when working in the ground_station package, telemetry reception, mission control interface, or real-time flight monitoring.
keywords	["ground station","ground_station","telemetry","mission control","monitoring","radio","RFD 900x","receiver","UART bridge","USB CDC"]

Ground Station - RFD 900x USB-UART Bridge

Role in System

The ground station is an RP2040 Embassy firmware (Adafruit Feather RP2040, same board as pico_logger) that bridges USB CDC serial and UART to interface with an RFD 900x-US radio modem. Primary use case is receiving telemetry from the rocket during flight.

Data flow: Computer <-> USB CDC <-> RP2040 <-> UART (57600 8N1, TX=GP0, RX=GP1) <-> RFD 900x

Project Structure

ground_station/
├── .cargo/config.toml  # thumbv6m-none-eabi target, picotool runner
├── build.rs            # Copies memory.x, sets linker flags
├── memory.x            # RP2040 memory layout (2MB flash, 256K RAM)
├── Cargo.toml          # Embassy dependencies
└── src/
    ├── main.rs          # Entry point, USB CDC + UART setup, command loop
    ├── protocol.rs      # Mode enum, DataPacket, EscapeDetector
    └── uart_bridge.rs   # UART rx/tx async tasks, inter-task channels

Build & Flash

cd ground_station
cargo build --release
cargo run --release  # Uses picotool to flash (device must be in BOOTSEL mode)

Target: thumbv6m-none-eabi (RP2040 Cortex-M0+)

Operating Modes

Command Mode (default)

• UART RX data forwarded to USB
• USB input interpreted as local commands

Command	Action
PING	Responds PONG\r\n
BOOTSEL	Reboot to BOOTSEL mode
STATUS	Show current mode and UART config
PASSTHROUGH	Enter transparent bridge mode
ATMODE	Enter AT config mode (handles +++ guard times)
SEND <data>	Send payload bytes through radio
HELP	List available commands

Passthrough Mode

• Fully transparent bidirectional USB <-> UART bridge
• All USB data forwarded to UART and vice versa
• Exit: 3x Ctrl-A (0x01 0x01 0x01) returns to Command mode

AT Config Mode

• For RFD 900x AT command configuration
• Entry sends +++ with 1-second guard times
• USB input forwarded to UART as AT commands
• UART responses forwarded to USB
• Exit: EXITAT (local) or ATO (also sent to radio)

Architecture

Async Tasks (Embassy)

• main - Init, USB CDC command loop, mode switching
• usb_task - Drives USB device stack
• uart_rx_task - Reads UART with 2ms inter-byte timeout batching into DataPackets
• uart_tx_task - Reads DataPackets from channel, writes to UART

Inter-Task Communication

Two Channel<CriticalSectionRawMutex, DataPacket, 8> statics:

• UART_TO_USB - Radio data → computer
• USB_TO_UART - Computer data → radio

DataPacket

64-byte buffer + length, Copy type for use in channels.

Hardware Configuration

• Board: Adafruit Feather RP2040
• USB: CDC ACM, VID=0x2e8a PID=0x000b, "Ground Station RFD Bridge"
• UART0: 57600 baud, 8N1, TX=GP0, RX=GP1, DMA channels 0/1
• Radio: RFD 900x-US (connected to UART0)

Key Gotchas

embassy-rp 0.9.0 UART Types

• UartTx<'d, M: Mode> and UartRx<'d, M: Mode> use Mode (Async/Blocking) as generic, NOT the peripheral type
• Uart::new() takes 7 args: (uart, tx_pin, rx_pin, irq_binding, tx_dma, rx_dma, config)
• UART requires interrupt binding even for DMA mode: UART0_IRQ => uart::InterruptHandler<UART0>
• Task function signatures use UartRx<'static, Async>, NOT UartRx<'static, UART0>

USB PID Allocation

• Pico Logger: 0x000a
• Ground Station: 0x000b

Related Skills

• pico-logger: Same board, similar Embassy patterns
• embassy-rp: Embassy HAL for RP2040
• pico-tooling: Flashing and serial monitoring