Flashing INAV Firmware via DFU

IMPORTANT: Use the fc-flasher Agent

When this skill is invoked, you MUST immediately use the Task tool with

subagent_type=fc-flasher

The

fc-flasher

• Automatic settings backup and restore
• MSP reboot to DFU mode
• Hex to bin conversion
• DFU flashing
• Verification

Example:

User: "Flash inav_9.0.0_MATEKF405.hex"
Assistant: [Immediately calls Task tool with subagent_type=fc-flasher and the hex file path]

Do NOT use manual DFU steps unless the fc-flasher agent fails or you're troubleshooting.

Manual DFU Flashing (Troubleshooting Only)

The information below is for troubleshooting when the automated agent doesn't work.

Prerequisites

Install dfu-util:

# Ubuntu/Debian
sudo apt install dfu-util

# Fedora
sudo dnf install dfu-util

# Arch
sudo pacman -S dfu-util

# Or download from source
# http://sourceforge.net/p/dfu-util

You'll also need objcopy (part of binutils, usually pre-installed):

# If needed, install gcc-arm-none-eabi or binutils
sudo apt install binutils-arm-none-eabi  # Ubuntu/Debian

Step 1: Put Flight Controller into DFU Mode

Choose ONE of the following methods:

Method A: Hardware Button

Press and hold the DFU/BOOT button on the board while plugging in USB.

Method B: Serial Command (Recommended: Use Helper Script)

Using the helper script (RECOMMENDED):

# Python version (requires pyserial)
.claude/skills/flash-firmware-dfu/reboot-to-dfu.py /dev/ttyACM0

# Install pyserial if needed:
pip3 install pyserial

Manual method (not recommended - race condition):

The correct sequence requires waiting for the actual CLI prompt, not just a fixed delay:

1. Send

   ####\r\n

   to enter CLI mode
2. Read from serial and wait for "CLI" string in response (timeout: 2 seconds)
3. Only after receiving CLI prompt: send

   dfu\r\n

4. Disconnect

Why simple echo + sleep doesn't work:

# DON'T DO THIS - race condition!
echo -ne '####\r\n' > /dev/ttyACM0
sleep 0.25  # Wrong! Doesn't wait for actual CLI prompt
echo -ne 'dfu\r\n' > /dev/ttyACM0

This fails because:

• It blindly sleeps without checking if CLI is ready
• If the FC takes >250ms to respond, the

  dfu

  command is sent too early
• The helper scripts properly wait for the "CLI" prompt before sending

  dfu

Method C: CLI Command

Connect with INAV Configurator or serial terminal and type:

dfu

Method D: MSP Reboot Command (INAV 9.x+)

Using MSP to reboot to DFU (most reliable programmatic method):

# Using mspapi2
from mspapi2 import MSPSerial

serial = MSPSerial("/dev/ttyACM0", 115200)
serial.open()

# Send MSP_REBOOT (68) with DFU parameter (1)
code, payload = serial.request(68, b'\x01')

serial.close()

# Wait for reboot
import time
time.sleep(2)

This is the most reliable programmatic method because it:

• Doesn't require CLI prompt timing
• Works through the MSP protocol
• Is supported by configurator and tools
• Provides proper backwards compatibility

Parameter values:

• b'\x00'

  or empty = normal reboot

• b'\x01'

  = reboot to DFU mode

Step 2: Verify DFU Mode

Check that the device is in DFU mode:

dfu-util -l

You should see a device with ID

0483:df11

Step 3: Convert HEX to BIN

DFU requires binary format, so convert the

.hex

cd inav/build
objcopy -I ihex inav_x.y.z_TARGETNAME.hex -O binary inav_x.y.z_TARGETNAME.bin

Example:

objcopy -I ihex inav_8.0.0_MATEKF405.hex -O binary inav_8.0.0_MATEKF405.bin

Step 4: Flash the Firmware

dfu-util -d 0483:df11 --alt 0 -s 0x08000000:force:leave -D inav_x.y.z_TARGETNAME.bin

Example:

dfu-util -d 0483:df11 --alt 0 -s 0x08000000:force:leave -D inav_8.0.0_MATEKF405.bin

Command Breakdown:

• -d 0483:df11

  - Target device ID (STM32 DFU)

• --alt 0

  - Alternative setting (default flash memory)

• -s 0x08000000

  - Start address (STM32 flash base)

• :force

  - Force write even if non-blank

• :leave

  - Exit DFU mode and run firmware after flashing

• -D <file>

  - Binary file to flash

Step 5: Verify

After flashing completes, the flight controller should automatically reboot and run the new firmware.

Connect with INAV Configurator to verify the version.

Complete Example Workflow

# 1. Build the firmware
cd inav/build
make MATEKF405

# 2. Put flight controller in DFU mode
# Option A: Hardware button (press BOOT button while plugging USB)
# Option B: Serial command (use helper script)
../.claude/skills/flash-firmware-dfu/reboot-to-dfu.py /dev/ttyACM0

# 3. Verify DFU mode
dfu-util -l

# 4. Convert hex to bin
objcopy -I ihex inav_8.0.0_MATEKF405.hex -O binary inav_8.0.0_MATEKF405.bin

# 5. Flash
dfu-util -d 0483:df11 --alt 0 -s 0x08000000:force:leave -D inav_8.0.0_MATEKF405.bin

Automated Script

For repeated flashing during development:

#!/bin/bash
# flash-firmware.sh

TARGET="MATEKF405"
SERIAL_PORT="/dev/ttyACM0"
HEX_FILE="inav_*.${TARGET}.hex"
SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

# Put FC into DFU mode using helper script
echo "Entering DFU mode..."
if ! $SCRIPT_DIR/.claude/skills/flash-firmware-dfu/reboot-to-dfu.py $SERIAL_PORT; then
    echo "ERROR: Failed to enter DFU mode!"
    exit 1
fi

# Note: Helper script already waits and verifies DFU mode

# Convert to bin
echo "Converting hex to bin..."
objcopy -I ihex $HEX_FILE -O binary ${HEX_FILE%.hex}.bin

# Flash
echo "Flashing firmware..."
dfu-util -d 0483:df11 --alt 0 -s 0x08000000:force:leave -D ${HEX_FILE%.hex}.bin

echo "Flash complete!"

Usage:

chmod +x flash-firmware.sh
./flash-firmware.sh

Troubleshooting

No DFU capable USB device found

Permission denied

sudo

Cannot open DFU device

udev Rules (Avoid sudo)

Create

/etc/udev/rules.d/45-stm32dfu.rules

# STM32 DFU Bootloader
SUBSYSTEM=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="df11", MODE="0664", GROUP="plugdev"

Then reload:

sudo udevadm control --reload-rules
sudo udevadm trigger

Add your user to the plugdev group:

sudo usermod -a -G plugdev $USER

Log out and back in for group changes to take effect.

Alternative Methods

INAV Configurator (GUI)

1. Open INAV Configurator
2. Click "Firmware Flasher"
3. Select "Load Firmware [Local]"
4. Browse to your

   .hex

   file
5. Click "Flash Firmware"

msp-tool (Command Line)

# Install msp-tool
go install github.com/fiam/msp-tool@latest

# Flash
msp-tool flash --port /dev/ttyACM0 inav_x.y.z_TARGETNAME.hex

flash.sh

See mwptools documentation

Safety Notes

• ALWAYS verify you're flashing the correct target for your hardware
• Backup your settings using CLI

  dump

  command before flashing
• Double-check file paths and target names
• Keep a known-good firmware hex file as backup

CLI Command Tools

This skill includes Python scripts for sending commands to the flight controller via CLI:

fc-cli.py - Modular CLI Command Tool

Send any CLI command to the flight controller:

# Show task execution times (useful for performance analysis)
.claude/skills/flash-firmware-dfu/fc-cli.py tasks

# Show firmware version
.claude/skills/flash-firmware-dfu/fc-cli.py version

# Show flight controller status
.claude/skills/flash-firmware-dfu/fc-cli.py status

# Reboot to DFU mode
.claude/skills/flash-firmware-dfu/fc-cli.py dfu

# Send any custom CLI command
.claude/skills/flash-firmware-dfu/fc-cli.py "get gyro_lpf1_static_hz"

# Specify custom serial port
.claude/skills/flash-firmware-dfu/fc-cli.py tasks /dev/ttyUSB0

Available built-in commands:

• dfu

  - Reboot to DFU bootloader mode

• tasks

  - Show task execution times

• status

  - Show flight controller status

• version

  - Show firmware version
• Any other CLI command - just pass it as an argument

How it works:

1. Opens serial connection to flight controller
2. Enters CLI mode by sending

   ####\r\n

3. Waits for "CLI" prompt (with timeout)
4. Sends your command
5. Reads and displays the response (except for

   dfu

   which disconnects)

Adding new commands: Edit

fc-cli.py

COMMANDS

COMMANDS = {
    'mycommand': {
        'handler': lambda cli: cmd_generic(cli, 'mycommand'),
        'description': 'Description of my command',
        'read_response': True,
    },
}

reboot-to-dfu.py - Simple DFU Reboot

Simple standalone script that only reboots to DFU mode (equivalent to

fc-cli.py dfu

.claude/skills/flash-firmware-dfu/reboot-to-dfu.py [port]

Use

fc-cli.py

USB Debugging

When USB MSC (mass storage) or CDC (serial) modes have issues, see:

claude/developer/docs/debugging/usb-msc-debugging.md

Quick commands:

lsusb -v | grep -A20 "STM"
dmesg | tail -50
cat /sys/bus/usb/devices/*/product

Related Skills and Agents

Skills:

• build-inav-target - Build firmware before flashing
• build-sitl - Test changes in SITL before flashing hardware
• msp-protocol - MSP protocol reference

Agents:

• fc-flasher - Automated flashing with settings preservation (RECOMMENDED)
• inav-builder - Build firmware for targets
• target-developer - Fix target configuration issues if hardware doesn't work after flashing

References

• Full documentation:

  inav/docs/development/Building in Linux.md

• USB debugging:

  claude/developer/docs/debugging/usb-msc-debugging.md