ardupilot/libraries/AP_Scripting/applets/param-set.md

Parameter Set Filter Script

Description

This Lua script adds a safty-focused layer to MAVLink parameter setting. When enabled, it intercepts all incoming PARAM_SET messages and only allows modification of a predefined whitelist of parameters.

This is especially useful in scenarios where parameter integrity is critical (e.g., automated testing, payload-hosted GCS systems, or shared telemetry environments).

When enabled, the script disables ArduPilot's default GCS handling for parameter writes and takes over that responsibility with additional filtering.

How It Works

• Intercepts MAVLink PARAM_SET messages targeted at the vehicle.
• Validates that the parameter ID is in the whitelist.
• Only whitelisted parameters will be updated.
• Dynamically toggles ArduPilot’s gcs:set_allow_param_set() based on enable state.

Requirements

• ArduPilot 4.7 or later with Lua scripting enabled (SCR_ENABLE = 1)
• copy the script to the vehicle autopilot's "scripts" directory
• The script must be placed in appropriate directories:

Parameters

This script introduces a new parameter table named PARAM_SET_. It includes:

Name	Type	Default	Description
ENABLE	int	1	Enables (1) or disables (0) the script

You can disable the script by setting PARAM_SET_ENABLE = 0. Note: disabling SCR_ENABLE while this script is actively blocking parameter sets is not recommended.

Whitelisted Parameters

Only the following parameters are allowed to be set when the script is enabled:

• MAV_OPTIONS
• PARAM_SET_ENABLE
• Battery parameters (e.g., BATT_ARM_MAH, BATT_FS_CRT_ACT, etc.)
• BRD_OPTIONS
• COMPASS_USE3
• Geofence and RTL parameters (e.g., FENCE_TYPE, RTL_ALT_M)
• LOG_*, LIGHTS_ON

(See the full script for the complete whitelist.)

Usage

1. Copy the script into the SD card's scripts directory.
2. Ensure SCR_ENABLE and PARAM_SET_ENABLE are both set to 1.
3. Reboot the autopilot or reload the script if necessary.

Logging & Debugging

The script sends diagnostic messages to the GCS:

• Allowed parameter updates show a param set received message.
• Blocked updates show a param set denied message with the offending parameter name.

Example output:

[param-set] param set received [param-set] param set denied (LOG_BACKEND_TYPE)

Limitations

• Only handles PARAM_SET messages (not PARAM_REQUEST_*).
• The parameter whitelist is hardcoded; changes require script edits.
• ArduPilot must support the gcs:set_allow_param_set() interface.
• parameter upload via FTP is denied when this script is running

Author

Contributed via PR #29989
May 2025