Firmware: Pixhawk 248

Here’s the full story of that firmware era.

Part 1: Understanding the Pixhawk Firmware Ecosystem

Before diving into the specifics of "248 firmware," it is critical to understand the two main firmware families running on Pixhawk hardware:

  1. ArduPilot (ArduCopter/ArduPlane): The most popular choice for DIY drones. Version numbers like 3.6.8, 4.0.7, or 4.5.0 are common.
  2. PX4 Pro: A more modular, real-time operating system (NuttX) based autopilot, often used in research and commercial applications.

Where does "248" fit in?
Historically, ArduCopter 3.6.8 was a landmark release. Some users internally labeled builds from the 3.6.x branch as "248" due to the final digits of specific commit hashes or bootloader identifiers (e.g., bootloader version 2.48). In many online forums (RCDiscuss, ArduPilot Discourse), "Pixhawk 248 firmware" has become shorthand for ArduCopter 3.6.8-3.6.12 optimized for FMUv2 boards with 1MB or 2MB flash. pixhawk 248 firmware

2. Hardware Architecture Under the Hood

The firmware for this target is tailored specifically to the limitations and features of the FMUv2 architecture. Understanding these constraints is key to understanding why the firmware is distributed the way it is.

The Core Specs:

  • Processor: STM32F427, Cortex-M4 core with FPU.
  • RAM: 256KB SRAM.
  • Flash: 2MB (Though older revisions often had a bug where only 1MB was accessible, necessitating a specific firmware build).
  • Sensors: Typically utilizing the MPU6000 Gyro/Accel and MS5611 Barometer.

The IO Processor: A defining feature of the 248 firmware is the utilization of a co-processor, the STM32F100 (IO MCU). This chip handles the direct PWM output for the main 8 channels, acting as a safety switch and fail-safe mechanism. The firmware ensures constant communication between the main Flight Management Unit (FMU) and this IO processor.

Peripherals & I/O

  • PWM/PPM output: Multiple PWM outputs, support for DShot, OneShot, and servo smoothing.
  • SBUS/DSM support: Multiple RC input protocols (PWM, SBUS, DSM, PPM, Spektrum).
  • CAN bus: UAVCAN support for external ESCs, GPS, odometry, and redundant peripherals.
  • Camera/Gimbal control: PWM or serial gimbal commands, camera trigger, and ROI for FPV.
  • Companion computer interface: High-bandwidth USB/serial bridge, MAVLink passthrough, USB mass storage for logs.

1. Superior Stability for Basic Multicopters

Version 3.2.4 (248) was the peak of the original "Inertial Navigation" (INAV) based EKF (Extended Kalman Filter). Pilots reported that 248 firmware offered: Here’s the full story of that firmware era

  • Silky smooth altitude hold without "bouncing."
  • Predictable loiter mode with minimal GPS glitching.
  • No "uncommanded descent" issues that plagued some later 3.5.x releases.

For cinematography drones and simple quadcopters, 248 firmware is considered rock solid.

Critical Warnings & Best Practices

  1. Do not confuse ArduPilot and PX4 firmware. Flashing the wrong one can cause sensor failures or bricking. Always match firmware to the bootloader type.
  2. Backup parameters before any firmware change.
  3. Verify hardware revision: Open the Pixhawk case – look for "2.4.8" printed on the PCB. If absent, treat it as a generic FMUv2 board.
  4. Calibrate after flashing: After loading firmware, always do accelerometer, compass, radio, and ESC calibration.

Performance & tuning

  • Real-time scheduling: Deterministic task scheduling, fixed-rate control loops (e.g., 1 kHz inner loop).
  • Low-latency I/O: DMA-driven sensors, async serial handling, optimized SPI/I2C drivers.
  • Tuning tools: Onboard autotune for PID, logging-assisted tune analysis.

4. Step-by-Step Flashing Guide (Using Mission Planner)

If you prefer Mission Planner (Windows only), often used with ArduPilot: Where does "248" fit in

  1. Setup: Connect the Pixhawk via USB.
  2. Select Port: Select the COM port (usually shows as a numbered port) and set Baud Rate to 115200. Click Connect (top left). Note: You generally need to disconnect before flashing.
  3. Firmware Tab: Go to the Initial Setup tab -> Install Firmware.
  4. Select Hardware:
    • Click Pixhawk4 (if available) or look for the icon matching your board.
    • Alternatively, select FMUv5 from the drop-down list if manually selecting.
  5. Select Version: Choose the latest stable version (e.g., Copter 4.5.x).
  6. Upload: Click the button to upload. The system will put the board into bootloader mode and write the firmware.