Segfault Rocket Avionics Firmware

Firmware for a TTGO T-Beam ESP32 board used as rocket avionics.

The firmware implements real-time sensor ingestion, Kalman filtering, state-dependent flash logging, custom LoRa telemetry/remote control, and a localized WiFi Recovery access point for post-flight log downloads.

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System Runtime Flow

The top-level execution is orchestrated in src/main.cpp:

1. Setup Sequence:
   • Initializes Serial console (debug mode).
   • Opens the non-volatile storage (NVS) flash partition.
   • Restores the saved FSM state from NVS (defaults to BeforeLaunch if empty).
   • Initializes hardware helper modules: FlightLogger and RecoveryService.
   • Attaches NVS parameters to the FlightFsm and StateLogic controllers.
   • Restores previous flight time and baseline parameters from NVS if booting into a post-launch state; otherwise, begins baseline calibration.
   • Initializes sensor buses and hardware pins (I2C PMU, barometric pressure, IMU, GPS UART, current sensor, Hall inputs, and parachute servo).
   • Initializes the LoRa radio module.
2. Main Execution Loop (loop()): Runs a cooperative tick-based loop without blocking operations or synchronous delays:
   • measurements.tick(nowMs): Samples all hardware sensors at the configured rate and updates the state estimate.
   • stateLogic.tick(...): Evaluates transition conditions, updates FSM states, controls telemetry intervals, and drives the parachute servo.
   • telemetry.tick(...): Transmits packet telemetry via LoRa when the active interval expires.
   • remoteControl.tick(...): Listens for incoming LoRa command overrides from the ground station between telemetry periods.

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Finite State Machine (Flight FSM)

The avionics state is managed centrally by a state machine containing five states:

1. BeforeLaunch: Telemetry runs at a slow heartbeat rate. Baselining calibration is active to settle sensor noise.
2. Armed: Telemetry runs at a slow heartbeat rate. State-dependent logging is active (recording only on acceleration events).
3. Flight: High-rate telemetry is enabled. Flight logging runs unconditionally. Baselining calibration is locked.
4. ApogeeReached: Triggers immediate deployment of the parachute servo, then transitions to ChuteDeployed.
5. ChuteDeployed: High-rate telemetry is enabled. Flight logging is active only when falling. The local WiFi Recovery AP is active.

State Transitions

• BeforeLaunch ➡️ Armed: Initiated manually or via a remote control state command.
• Armed ➡️ Flight: Automatically triggered when Z-axis vertical acceleration (compensated by the ground baseline) exceeds the configured launch threshold for the required minimum duration.
• Flight ➡️ ApogeeReached: Automatically triggered when either:
  • Primary Trigger: Filtered altitude falls below the maximum altitude reached by the configured drop margin, and the vertical velocity falls below the apogee threshold.
  • Backup Trigger: The flight timer exceeds the apogee failsafe duration.
• ApogeeReached ➡️ ChuteDeployed: Transitions automatically on the next clock cycle after command deployment is dispatched to the parachute servo.

State-Transition Event Actions

• Entering Armed: Automatically triggers a flash erase of the flightlog partition to clear old flight logs and prepare sectors for high-speed writes.
• Entering Flight: Disables the sensor baselining calibration, locks the current ground altitude and gravity acceleration offsets, writes the baseline parameters to NVS, and starts the elapsed flight timer.
• Exiting Flight back to pre-launch states: Re-enables the sensor baselining calibration.
• Entering ChuteDeployed: Powers up the WiFi radio, configures the soft Access Point, and spins up the background web server task on Core 1.
• Exiting ChuteDeployed: Shuts down the WiFi AP, closes the web server, and disables the WiFi radio.

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Telemetry and Logging Services

LoRa Telemetry Transmission

Telemetric snapshots are formatted and dispatched using non-blocking packet transmits over the LoRa transceiver. Telemetry intervals are dynamic and managed by the current FSM state (slow heartbeat pre-flight, fast telemetry during flight/descent).

The transmitted telemetry packet includes:

• Frame sync words and timestamp offsets.
• Active FSM state flags.
• Raw IMU linear accelerations and angular gyro rates.
• Kalman-filtered altitude (AGL).
• Raw barometric pressure.
• Triboelectric sensor probe voltage.
• Main battery voltage.
• GPS coordinates and fix quality.
• Kalman-filtered vertical velocity. -KY-024 Hall sensor values.

State-Dependent Flash Logging

High-speed flight data is written to a dedicated raw SPI flash partition (flightlog). To conserve flash memory write cycles and queue buffers, logging uses state-dependent rules:

• Armed: Logs only when Z-axis acceleration rises above the launch baseline.
• Flight & ApogeeReached: Logs unconditionally at the high-frequency rate.
• ChuteDeployed: Logs only when falling (vertical velocity is below a negative threshold).

The log packet includes all telemetry parameters plus raw GPS satellites, GPS fix validity, system sensor health flags, internal board temperature, and is protected with a Fletcher16 checksum.

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Baselining and Calibration

Before launch, the avionics runs an exponential moving average over the barometric pressure and Z-axis accelerometer readings to establish a ground baseline (altitude above sea level and vertical gravity offset).

When launch is detected, baselining is locked and stored in NVS. This baseline is used throughout the flight to compute:

• Filtered AGL (above ground level) altitude.
• Gravity-compensated vertical acceleration for the state estimator.
• Re-baselining is allowed prior to launch via remote command.

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Remote Control Override System

In between telemetry transmissions, the LoRa radio enters a non-blocking receive window to process incoming commands. Commands can override the autonomous logic to:

• Deploy the parachute (forces servo to deploy angle).
• Stow the parachute (forces servo to stow angle).
• Set the active FSM state manually.
• Trigger a sensor baseline reset (allowed only when not in flight).

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Recovery Access Point & File Server

Upon entering the ChuteDeployed state, the avionics spins up a WiFi soft Access Point and hosts a localized HTTP web server.

Connecting to the AP and requesting the root URL starts a raw binary stream of the entire flash logging partition as a file download. The server processes downloads in small blocks, yielding to the system task scheduler to prevent triggering the hardware watchdog timer during transfer.