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Control code for the autonomous submarine, Marlin. 
Copyright (C) 2019 AVBotz


REQUIREMENTS 

	Unix environment w/ connected Arduino.
	Platformio. (sudo pip install -U platformio) 
	Tmux (recommended, sudo apt-get install tmux)

COMPILING

	sudo make (local compile)
	sudo make upload (compiles and uploads onto board, if connected)
	sudo ./comms.sh && sudo chmod 666 /dev/ttyACM* (init serial communication)

STARTUP

	After compiling and uploading, run tmux in a terminal. Split the tmux window
	into two panes. Run "cat < /dev/ttyACM*" in one and "cat > /dev/ttyACM*" in 
	the other. The former pane is the DISPLAY pane, it will show the output from
	Nautical. The latter is the COMMAND pane, it is where Nautical receives its
	input.

CONFIG

	All important configs are located and explained in "include/config.h". 

COMMANDS

	(Check "src/main.cpp" for full list of commands.)

	+---------------------+----------------------+-------------------+
	|        Input        |     Description      |      Output       |
	+---------------------+----------------------+-------------------+
	| a                   | Kill switch (1=on).  | %i                |
	| c                   | Sub location.        | %f %f %f %f %f %f |
	| d                   | Sub destination.     | %f %f %f %f %f %f |
	| p %f                | Set power (0-1).     | N/A               |
	| s %f %f %f %f %f %f | Set destination.     | N/A               |
	| r %f %f %f %f %f %f | Add relative state.  | N/A               |
	| h                   | Raw heading (0-360). | N/A               |
	| x                   | Reset all states.    | N/A               |
	+---------------------+----------------------+-------------------+

	Each 6 %f's represent a state, or sub position. The order of the numbers is
	X, Y, Z, Yaw, Pitch, Roll. This is relative to a North-East-Down coordinate
	frame.

DOCUMENTATION

	All of the header files are documented using Doxygen. They describe how all
	of the functions work and interact each other at a higher level. More
	specific implementation details are explained using regular comment blocks
	in the .c/.cpp files. 

	For general questions about the software stack, contact David Zhang.
	Questions about low-level drivers can also be directed towards Seth Girvan
	(AHRS, M5) and Timothy Kanarsky (DVL).

REMOTE

	Marlin can also be controlled with WASD and arrow keys over a socket. To do
	this, ensure that the remote_control node on Marlin's ROS stack is running
	first. Then run "sudo python manual.py".

ADDITIONAL 

	Nautical uses a Kalman filter to reduce noise from DVL and other sensor
	readings. However, the current movement model doesn't represent Marlin's
	movement well enough to provide a substantial upgrade over raw DVL data.

	Nautical also needs better PID tunings or a slight change in the orientation
	matrix. Marlin tends to pitch downward and strafe a bit to the right when
	moving forward at high speeds.

	Nautical can also be improved with quaternions over euler angles (:P).

LICENSE

	This code is under the MIT license. Check the LICENSE file for more details.