find-param

name	find-param
description	Find ArduPilot parameter definitions in C++ source code. Use when the user asks about a parameter's definition, range, units, default value, or where it's declared.
argument-hint	<PARAM_NAME>
allowed-tools	Grep, Glob, Read

Find ArduPilot Parameter Definition

Search for the parameter $ARGUMENTS in the ArduPilot codebase.

Search Strategy

1. Find the parameter documentation block

ArduPilot parameters have documentation blocks like:

// @Param: RTL_ALT
// @DisplayName: RTL Altitude
// @Description: The altitude the vehicle will return at.
// @User: Standard
// @Units: cm
// @Range: 200 8000

Search for the @Param: line:

Grep for: @Param:\s*$ARGUMENTS

2. Find the AP_Param declaration

Parameters are declared as class members:

AP_Int16 rtl_alt;
AP_Float alt_hold_p;
AP_Int8 some_flag;

The parameter table binds name to variable:

// @Param: RTL_ALT
AP_GROUPINFO("RTL_ALT", 1, Mode, _rtl_alt, 1500),

Search for the AP_GROUPINFO or AP_SUBGROUPINFO line:

Grep for: AP_GROUPINFO.*"$ARGUMENTS"

3. Find where it's used

Search for the variable name in code to understand its effect.

Key information to extract

When you find the parameter, report:

• Full name (e.g., RTL_ALT)
• Display name and description
• Type (Int8, Int16, Int32, Float)
• Units (cm, m, cdeg, etc.)
• Range or Values (enumeration)
• Default value (from AP_GROUPINFO)
• File location where it's defined
• Which vehicle(s) use it

Common parameter table patterns

// Simple parameter
AP_GROUPINFO("NAME", index, ClassName, member_var, default_value),

// Flags variant (e.g., read-only)
AP_GROUPINFO_FLAGS("NAME", index, ClassName, member_var, default_value, AP_PARAM_FLAG_ENABLE),

// Nested group
AP_SUBGROUPINFO(member, "PREFIX_", index, ClassName, SubClass),

// Parameter from another class
AP_SUBGROUPPTR(pointer, "PREFIX_", index, ClassName, SubClass),

Parameter naming convention

• Uppercase with underscores: RTL_ALT_MIN
• Most important word first: RTL_ALT not ALT_RTL
• Prefixed by subsystem in parameter tables