pad_link_central_example.py

Minimal BLE central for the AURORA pad-link.

This script is the smallest thing that talks to a rocket running CONFIG_AURORA_PAD_LINK=y. It scans for the rocket’s advertised service, connects, reads the two static characteristics (board name and SM type), and then subscribes to the live ones (SM state and computed kinematics) so each new value is printed as it arrives.

It is meant as a reference, not a finished ground station. Use it to:

• test the rocket-side firmware after enabling the pad link (you should see at least the board id and the IDLE state),

• see how to decode the wire layouts documented in Pad Link in a real client,

• copy/paste pieces into a fuller UI (a Tk dashboard, a logger, the launchrail’s own central).

Wire contract

Mirrors aurora/lib/pad_link/pad_link.c.

Important

If the C-side struct or a UUID changes, the constants here must change too.

Characteristics:

Characteristic	Description
SERVICE_UUID	primary service to filter on during scan
UUID_BOARD	UTF-8 string, board identifier (e.g. board name)
UUID_SMTYPE	uint8, identifies which sm_state enum is in use
UUID_STATE	uint8, current SM state (notify-capable)
UUID_COMP	packed struct, computed kinematics (notify-capable)
UUID_RAW	packed struct, raw IMU+baro. not used here (optional)

Computed payload (28 bytes, little-endian):

uint32_t uptime_ms, float altitude_m, float velocity_m_s,
float yaw_deg, float pitch_deg, float roll_deg, float accel_vert_m_s2

Prerequisites

• Python 3.9+

• pip install bleak

• A BLE-capable host (built-in adapter on Linux/macOS/Windows, or a plugged-in USB BLE dongle).

• On Linux the user usually needs to be in the bluetooth group, or the script has to be run with sudo.

Running

python3 pad_link_central_example.py

You should see one connection line and then a stream of “state:” and “t=…” prints. The script exits after 60 seconds; raise the asyncio.sleep argument or wrap the body in a while True for longer sessions.

Notes for first-time users

• Default ATT MTU (23 B) is enough: read_gatt_char and notifications transparently do long reads for payloads larger than the MTU. Negotiating a bigger MTU (BleakClient(..., mtu=247)) just makes them faster.

• The first read of UUID_STATE before the rocket’s state machine has run even once returns 0 (= IDLE). Values stabilise within milliseconds of boot.

• Disconnects are normal and silent. The rocket re-starts advertising automatically. Wrap the body in a reconnect loop if you want the script to survive them.