# 2020q3 專題: Game Boy 模擬器 + JIT 編譯器
> * [RinHizakura 的工作區](https://hackmd.io/@RinHizakura/SkvY4N9cv)
> * [nelsonlai1 的工作區](https://hackmd.io/@nelsonlai1/GBJIT)

## 目標
* 改進[給定的 Game Boy 模擬器](https://github.com/sysprog21/jitboy)，排除已知問題，提升其執行效率及其相容性
* 透過 [GBIT](https://github.com/koenk/gbit) 確保程式碼實作的相容性和正確性
* 量化分析動態編譯器的效率，並尋求效能改進的方案
* 善用 [perf](http://www.brendangregg.com/perf.html) 和 GNU Toolchain

## 準備工作
* 觀看 [The Ultimate Game Boy Talk](https://media.ccc.de/v/33c3-8029-the_ultimate_game_boy_talk) 演講錄影，得知 Game Boy 模擬器的運作
* 研讀 [Gameboy Overview](https://thomas.spurden.name/gameboy/)，理解 Game Boy 硬體和相關模擬器的撰寫
* 對應的原始程式碼: [gameboy](https://github.com/tcrs/gameboy)
* 研讀 [Z80 Emu Evolution](https://floooh.github.io/2017/12/10/z80-emu-evolution.html) 以理解模擬器設計考量。注意: Game Boy CPU 使用 Z80 的客製化版本，和原本的 Z80 不相容
* 研讀 [Game Boy 遊戲軟體發展](http://140.134.131.145/upload/paper_uni/912pdf/910211.pdf)，理解 Game Boy 產品、硬體資訊、記憶體映射，及 GBDK 流程

## Game Boy 硬體和模擬器設計
> [Game Boy 的硬體設計與運作原理](https://hackmd.io/@RinHizakura/BJ6HoW29v)

## 現有的 Game Boy 模擬器
* [binjgb](https://github.com/binji/binjgb)
* 可[在網頁瀏覽器中啟動](https://binji.github.io/binjgb/)
* Convenient Python test harness using hashes to validate
* Debugger with various visualizations
* [jgbc](https://github.com/jamie-mh/jgbc)
* 實作完整
* 內建測試
* [SameBoy](https://github.com/LIJI32/SameBoy)
* Supports Game Boy (DMG) and Game Boy Color (CGB) emulation
* High quality 96KHz audio
* Battery save support
* Save states
* Advanced text-based debugger with an expression evaluator, disassembler, conditional breakpoints, conditional watchpoints, backtracing and other features
* Several [scaling algorithms](https://sameboy.github.io/scaling/) (Including exclusive algorithms like OmniScale and Anti-aliased Scale2x; Requires OpenGL 3.2 or later or Metal)
* [PlutoBoy](https://github.com/RossMeikleham/PlutoBoy)
* 非常完整
* [GBC](https://github.com/koenk/gbc)
* When the emulator detects unexpected behavior (e.g., accessing an unknown memory region), it will drop into a built-in debugger.

## [給定的 Game Boy 模擬器](https://github.com/sysprog21/jitboy)

1. 取得 `jitboy` 原始程式碼:

    $ git clone https://github.com/sysprog21/jitboy

2. 安裝 SDL2 套件
3. 編譯 (目前僅能在 GNU/Linux 平台運作)

    $ cd jitboy
    $ make

4. 取得 [Super Mario Land](https://wowroms.com/en/roms/nintendo-gameboy/super-mario-land-world/10202.html)，解開下載的 ZIP 檔案，將 `Super Mario Land (World).gb` 重新命名為 `mario.gb`
6. 執行 `build/jitboy mario.gb`

## Thread Sanitizer (tsan)

* 參見 [ThreadSanitizerCppManual](https://github.com/google/sanitizers/wiki/ThreadSanitizerCppManual) 和 [Thread Sanitizer and Static Analysis](https://developer.apple.com/videos/play/wwdc2016/412/)
* `jitboy` 已整合 tsan:

    make clean
    make sanitizer

* `jitboy` 執行過程中會遇到若干 [data race](https://en.wikipedia.org/wiki/Race_condition#Data_race)，應該予以排除

## 動態編譯器原理
* [Going faster with Just-In-Time compilation](https://github.com/jorgemarsal/jekyll-now/blob/master/_posts/2016-01-14-going-faster-with-just-in-time-compilation.md): 透過一個簡單的案例，說明適度運用 JIT 編譯為何可在執行時期帶來加速
* [Interpreter, Compiler, JIT from scratch](https://www.slideshare.net/jserv/jit-compiler)
* [虛擬機器設計與實作](https://hackmd.io/@sysprog/SkBsZoReb)
* [Unofficial DynASM Documentation](https://corsix.github.io/dynasm-doc/reference.html)
* 使用 [DynASM](https://luajit.org/dynasm.html) 的案例
* [LuaJIT](https://luajit.org/)
* [Pyston v2](https://blog.pyston.org/2020/10/28/pyston-v2-20-faster-python/)
* [Opcache JIT for PHP](https://github.com/php/php-src/tree/master/ext/opcache/jit)
* [PWASM](https://github.com/pablotron/pwasm): WebAssembly
* [Wasmer](https://github.com/wasmerio/wasmer): WebAssembly
* [libsregex](https://github.com/openresty/sregex): A non-backtracking NFA/DFA-based Perl-compatible regex engine library for matching on large data streams

## 內建 JIT 的 Game Boy 模擬器
* [gbemuc](https://github.com/mkilgore/gbemuc): 使用 libJIT
* [GbJit](https://github.com/iburinoc/gbjit)

## Instruction Tester
* [GBIT](https://github.com/koenk/gbit): Game Boy Instruction Tester
* Tests all instructions of a Game Boy CPU against a known-good implementation to detect implementation bugs.
* Useful for testing and debugging, especially early on in Game Boy emulator development where test ROMs do not run yet.
* TODO: 整合 [GBIT](https://github.com/koenk/gbit)，讓 JIT 編譯後的機械碼得以通過驗證
* TODO: 量化分析純粹直譯器和動態編譯器的效能表現