Add Parameter Group system documentation for developers

[sensei-hacker]

User description

Summary

Add comprehensive developer documentation for INAV's Parameter Group (PG) system to help developers understand when to increment PG version numbers and how to register parameter groups correctly.

Changes

• Add docs/development/parameter_groups/README.md with practical guide
• Documents compile-time registry using linker sections
• Explains version validation mechanism in pgLoad()
• Provides clear rules for when to increment PG versions
• Includes complete working examples based on actual code

Key Topics Covered

• How the PG registry works (linker sections, __pg_registry_start/end)
• Version encoding in top 4 bits of PGN field
• Version checking: pgLoad() resets to defaults on mismatch
• When to increment version (struct layout changes)
• Registration macros (PG_REGISTER_WITH_RESET_TEMPLATE, etc.)
• Complete examples developers can copy

Documentation Approach

• Based only on verified code (parameter_group.h/c)
• Conservative recommendations (increment version when in doubt)
• References real examples (blackbox config)
• Compared with Betaflight PG documentation for consistency

Related Context

• Addresses confusion seen in PR Blackbox - remove unused setting  #11236 (field removal requiring version increment)
• References PR [GF/LF] Fix PG resets for global functions and logic functions #5308 (reset function usage)
• References PR Update references to that should be control_profile #11122 (renaming without version increment)

---

PR Type

Documentation

---

Description

• Add comprehensive Parameter Group system documentation for developers

• Explains compile-time registry using linker sections and version validation

• Documents when to increment PG version numbers with practical examples

• Provides complete working examples and registration macro reference

---

Diagram Walkthrough

flowchart LR
  A["Developer needs PG guidance"] --> B["README.md documentation"]
  B --> C["How PG registry works"]
  B --> D["Version management rules"]
  B --> E["Complete code examples"]
  C --> F["Linker sections and macros"]
  D --> G["When to increment versions"]
  E --> H["Ready to implement PG"]

Loading

File Walkthrough

Relevant files

Documentation

README.md Parameter Group system developer guide                                      docs/development/parameter_groups/README.md New comprehensive documentation file covering Parameter Group system architecture Explains registration mechanism using linker sections and compile-time registry Documents version checking behavior in pgLoad() and when to increment versions Includes practical code examples for declaring, registering, and accessing parameter groups Provides reference tables for registration macros and common patterns Addresses real-world scenarios like field removal with version increment examples +257/-0

---

[qodo-code-review]

PR Compliance Guide 🔍

All compliance sections have been disabled in the configurations.

[qodo-code-review]

Suggestion: Update the documentation snippet to show basic input validation (e.g., from != NULL and size > 0) before calling memcpy, since real callers may pass invalid pointers/sizes; keep a safe fallback of “defaults only” when validation fails. [Learned best practice, importance: 6]

Suggested change

	```c
	void pgLoad(const pgRegistry_t* reg, int profileIndex,
	const void *from, int size, int version)
	{
	pgReset(reg, profileIndex); // Always reset to defaults first
	if (version == pgVersion(reg)) {
	// Only copy if versions match
	const int take = MIN(size, pgSize(reg));
	memcpy(pgOffset(reg, profileIndex), from, take);
	}
	// If version mismatch: defaults remain, no corruption
	}
	```
	```c
	void pgLoad(const pgRegistry_t* reg, int profileIndex,
	const void *from, int size, int version)
	{
	pgReset(reg, profileIndex); // Always reset to defaults first
	if (version == pgVersion(reg) && from != NULL && size > 0) {
	// Only copy if versions match and input is valid
	const int take = MIN(size, pgSize(reg));
	memcpy(pgOffset(reg, profileIndex), from, take);
	}
	// Otherwise: defaults remain, no corruption
	}