start game bridge code

doc/gamebridge.org

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+#+TITLE: gamebridge
+
+An interface between Super Mario 64 and just about anything else your heart
+desires. 
+
+* High level ideas
+
+the rust program has two threads, one is getting the inputs from $SOMEWHERE and
+the other is doing the file I/O to the game \\
+the game bridge thread has two file descriptors open, a fifo for feeding inputs
+to the game and a fifo opened by the game for signaling vblanks \\
+the game will then write a readiness signal to the rust program and read the
+button data fifo \\
+then things will progress normally \\
+the getting the input thread of the rust program will have some logic for
+telling how long ago it got liveness of the input source (explicitly vaguely
+defined to allow a controller to sit there and do nothing as long as it still
+exists), and then "sticking" it until, say, 10 frames have passed and then it
+will block infinitely, freezing the game in place
+
+* Goals
+
++ Blocking, synchronous rust as much as possible
++ unix fifos are great, let's use them
+
+* Protocol
+
+The protocol between the game and the bridge will be as follows (based on the
+[[http://tasvideos.org/EmulatorResources/Mupen/M64.html][Mupen64 demo format]]). Two unix fifos will be created by the bridge. 
+
+The game and the bridge will both need to take care that the files are opened in
+*unbuffered I/O modes*. This can be done with 
+=setvbuf( f, (char *)NULL, _IONBF, 0 );= in C and is the default in Rust.
+
+The first one will be called =vblank= and will then be opened by the game in
+write mode when it starts. The bridge will open this fifo in read mode. 
+
+The second one will be called =input= and will be opened by the game in read
+mode. The bridge will open this fifo in write mode.
+
+On every frame, the game will write the text ="OK\n"= to the vblank fifo. This
+will signal the bridge that it should write four bytes of data to the input
+fifo, conforming to the [[http://tasvideos.org/EmulatorResources/Mupen/M64.html#ControllerData][Controller Data]] specification of the Mupen64 format.
+This data will be interpreted by the game as actions for Mario to take.
+
+The bridge *MUST* block on waiting for the vblank fifo to be written to by the
+game and the game *MUST* block on the input fifo being written to by the bridge.

gamebridge/.gitignore

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+/target

gamebridge/Cargo.toml

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+[package]
+name = "gamebridge"
+version = "0.1.0"
+authors = ["Christine Dodrill <me@christine.website>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

gamebridge/src/main.rs

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+fn main() {
+    println!("Hello, world!");
+}