Rearchitecting Software: Source Code Comprehension and Refactoring Applied to Flight Software and Simulation

1 Introduction
	1.1 Only the source code tells the full story
	1.2 The Myth of Code Readability
	1.3 Comprehending Code in Embedded, Distributed Systems
	1.4 Not programming advice
2 The Science Behind Code Comprehension
	2.1 Code comprehension models
	2.2 Code Comprehension Typical Activities
	2.3 The Necessary Mental Flow7F
	2.4 Build Systems & Tools (A Blessing and a Curse)
	2.5 Autotools and the GNU Build System8F
		2.5.1 Files Appearing out of Nowhere
	2.6 CMake
	2.7 Meson9F
		2.7.1 Using Meson
		2.7.2 Adding dependencies
	2.8 Need For Speed: Ninja10F
		2.8.1 Design goals of Ninja
		2.8.2 Using Ninja
		2.8.3 Variables
		2.8.4 Rules
		2.8.5 Build statements
	2.9 Make vs. Meson vs. Ninja
3 Architectural Styles
	3.1 Monolithic
	3.2 Microservices
	3.3 Layered
	3.4 Component-Based (“The AppStore”)
	3.5 Pipes and Filters
	3.6 Front and Back End
	3.7 Client-Server
	3.8 Publisher-Subscriber
	3.9 Event-Driven
	3.10 Middleware
	3.11  Service-Oriented
	3.12 Conclusion
		3.12.1 Good architecture is simple architecture
4 Tearing Software Down
	4.1 JSBSim Teardown
		4.1.1 Starting from scratch
		4.1.2 JSBSim In Slow-Motion: Step-by-step analysis
			4.1.2.1 The FGModel Base Class
			4.1.2.2 Properties
			4.1.2.3 Models
			4.1.2.4 JSBSim Initialization and Execution
	4.2 Core Flight System Teardown
		4.2.1 Starting from scratch (again)
		4.2.2 Compilation Success
		4.2.3 cFS In Slow motion
			4.2.3.1 Application Startup
			4.2.3.2 API Initialization
			4.2.3.3 Share Memory Initialization and data structure
			4.2.3.4 Creating A Virtual File System
			4.2.3.5 Calling the Executive Entry Point
			4.2.3.6 Dynamic and Static Application Loading and the challenge of debugging shared libraries
			4.2.3.7 Writing our first application
			4.2.3.8 Yes, it does; The Application Runs
			4.2.3.9 Software Bus, Pipes, Events, Tables, Commands and Telemetry
			4.2.3.10 Receiving Commands
			4.2.3.11 Sending Telemetry
	4.3 Recapping
5 Hooking JSBSim and cFS Together
	5.1 Writing an application in cFS that interacts with models in JSBSim
	5.2 Querying  JSBSim properties from cFS
	5.3 Refactoring cFS to work with streaming sockets
	5.4 Refactoring JSBSim’s telnet server, slightly
	5.5 Decoding the telemetry on the ground
	5.6 Showing and plotting the telemetry
	5.7 Setting Properties
	5.8 Reading from “real” on-board sensors
		5.8.1 Creating Our Own Sensor
	5.9 Adding more variables and some 3D visualization in real time
	5.10 Sending Commands to CFS
		5.10.1 Space Packet Protocol
		5.10.2 Sending Space Packets to cFS
			5.10.2.1 Function/command code
		5.10.3 Creating our first command (Throttling the Engines)
	5.11 Commanding control surfaces
	5.12 Recapping
6 Writing a Roll/Pitch Controller for a Boeing 737 in cFS
	6.1 Seeking stabilized pitch
	6.2 Flight Control Channels
	6.3 A Poor Man’s Fly-By-Wire
		6.3.1 Wing Leveling
		6.3.2 Commanding Some Roll Angle
	6.4  Summary
7 Conclusion