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File structure

• Libraries: Userland/Libraries/{LibC, LibGUI...}
• Games: Userland/Games/{Snake, Solitaire...}
• Applications: Userland/Applications/{Calculator, Calendar...}

Ninja

SerenityOS is built using CMake and Ninja.

• Target: output files of the build process (executables, libraries).
• Use Ninja with CMake: cmake -G Ninja (generates a build.ninja file)
• Build target: ninja

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Electronic components

• Breadboard: Rectangular plastic board with tiny holes to insert electronic components in them.
• Jump wire: Electrical wire used to interconnect components.
• Transistor: Used to amplify current, switch on/off the flow of current, and to construct logic gates.
• Diodes: Allows the flow of current in one direction & blocks the other direction (like a valve).
• Resistors: Limits the flow of current.
• Capacitor: Stores and releases electricity (like a temporary battery).
• LED: emits light when current flows through it.
• Arduino devices:
• Sensors: Used to monitor physical phenomena (e.g. temperature, humidity, motion, light...).

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C++ syntax

List initialization

Advantage: Doesn't allow narrowing, i.e. the following throws an error:

int i {2.0f};

Direct and copy initialization

Advantage: Doesn't create a copy (practical for objects):

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Below some notions about USB that could be useful to access USB devices programatically with [libusb]. For more details refer to [USB2.0 specification][usb2-specification].

Terminology

• Host: Computer.
• USB device: Peripheral connected to computer via USB.
• Hub: USB device providing additionnal connections to the USB.
• IRQ (Interrupt request): a hardware signal from device requesting attention from host.
• Pipe: Logical abstraction for associating device's endpoint and host's software. There two types of pipes:
  • Stream pipe: data no USB-defined structure.
• Message pipe: data has a USB-defined structure.

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OSI model

For systems interconnections in a network, and has 7 layers (from top to bottom):

• Application: Closest to user, e.g. HTTP, FTP...
• Presentation: Encryption/Decryption, Compression/decompression, e.g. jpeg, mpeg...
• Session: e.g. sync file transfers with checkpoints (to avoid restarting from beginning on failure).
• Transport: Flow and error control, e.g. TCP, UDP
• Network: breaks/assembleds data into packets, routing, e.g. IP
• Data link: connects devices that are physically in the same network, e.g. Ethernet, MAC
• Pyhsical: bit (raw data), e.g. cables

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SF2 format

• File format (binary) storing multiple instruments.
• Stores instrument samples to play MIDI.
• Samples are stored:
  • For each note of an instrument (e.g. all piano keys).
  • Possibly multiple velocities by key (how hard the note was struck).
• [Polyphone][polyphone] can be used to read sf2 files.
• [soundfont-fluid][soundfont-fluid] and [freepats-general-midi][freepats-general-midi] provide free samples in sf2 format (installed to /usr/share/soundfonts/).
• Jack2: is an audio server like pulseaudio and alsa but professional audio production thanks to its low latency:

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Dependencies

$ sudo pacman -Sy raylib

How to run

$ mkdir build
$ cd build
$ cmake .. && make -j

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• Modes:
  • Playback: Emit sound from speaker by writing data to output buffer (in callback).
  • Capture: Extract sound from microphone by reading data from input buffer (in callback).
• Sample: Single unit of audio data (when format = f32, a sample is a float in [-1, 1]).
• Frame (PCM Frame): Groups of samples having as many samples as the number of channels (stereo: 1 frame = 2 samples, mono: 1 frame = 1 sample).
• Sample rate: Number of frames processed each second expressed in Hz (e.g 44100 Hz).
• Device: Abstraction for a physical device.
• Callback: Function used to deliver data to/from the device async.
• Data source: Used for retrieving audio data from a source (e.g. decoder, waveform for generrating sine waves...).
• Decoder: Used for reading audio files (wav, mp3, flac).

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From the [hello world example][hello-world]:

• Coordinate system: y-axis points upwards and gravity downwards.
• Units: meters, kilograms, and seconds
• Area density: mass / area, and expressed in kg/m^2
• Fixture: Used to attach a shape to the body
• Shape: its coords are local to the body
• Static body: mass ~> oo (stored = 0 in box2d)
• Dynamic body: moves in response to forces
• FPS: 60 frames/sec = freq => delta_t = 1/60 sec
• Constraint solver: Iterates over constraints a number of times (two phases: velocity and position phases)

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D-Bus

• Interprocess communication (IPC) system for apps.
• Runs as a service.
• Two buses:
  • System bus: e.g. to notify about hardware connect/disconnect. Its service: systemctl status dbus.
  • Session bus: Specific to user sessions, e.g. communication between Gnome components. Its service: systemctl --user status dbus.
• dbus-run-session <cmd>: Starts a new session bus and run cmd in that session (to have access to the session dbus for IPC):
  • e.g gnome-shell --nested: Start Gnome within an existing session (for dev. & testing) without affecting the primary UI.

Extensions