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Run npx skillmds@latest add vizigr0u/backend in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

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Is Backend free to use?

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Who published Backend?

vizigr0u (@vizigr0u) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Backend by vizigr0u — Agent Skill

Name: Backend
Author: vizigr0u

File contents

You are working on the AssemblyScript backend of SvelteBoy, a GameBoy DMG emulator that compiles to WebAssembly.

Key Facts

Language: AssemblyScript (TypeScript-like, compiles to WASM via asc)
Entry point / public API: assembly/index.ts — all exports must be declared here
Main loop: assembly/emulator.ts — Emulator.Run() ticks CPU, Timer, PPU, DMA each cycle
Build: pnpm run asbuild:debug (dev) or pnpm run asbuild:release (prod)
Output: build/backend.wasm + build/backend.js (auto-generated ESM bindings)
Tests: pnpm test — runs suites in assembly/tests/

Module Map

Area	Path	Key files
CPU	`assembly/cpu/`	`cpu.ts` (registers/state), `opcodes.ts` (256+256 CB-prefix decode), `alu.ts`, `interrupts.ts`
PPU	`assembly/io/video/`	`ppu.ts` (main renderer), `scanlineRenderer.ts`, `pixelFifo.ts`, `oam.ts`, `dma.ts`
APU	`assembly/audio/`	`apu.ts` (core), `render.ts` (sample gen), `PulseChannel.ts`, `WaveChannel.ts`, `NoiseChannel.ts`
Memory	`assembly/memory/`	`memoryMap.ts` (address dispatch), `mbc1/2/3.ts` (bank controllers), `savegame.ts`
I/O	`assembly/io/`	`joypad.ts` (input), `timer.ts` (DIV/TIMA), `serial.ts`
Debug	`assembly/debug/`	`debugger.ts` (breakpoints), `debugInfo.ts` (snapshots), `disassemble.ts`

WASM Memory Layout (linear, flat)

0x00000000  VRAM       (16KB)
0x00004000  OAM        (160B)
0x000040A0  Ext RAM    (512KB, cartridge)
0x000840A0  Work RAM   (32KB)
0x0010C0A0  I/O Regs   (128B)
0x0010C120  High RAM   (128B)
0x0010CBA4  Cart ROM   (up to 8MB)

AssemblyScript Gotchas

No closures capturing this — use module-level functions or static class methods
Typed arrays are value types: Uint8Array, Int16Array, etc. are first-class
memory.data<u8>(offset) for direct memory reads; use store<u8>(ptr, val) / load<u8>(ptr) for raw access
No Map/Set generics with reference types — use StaticArray or custom structures
Exported functions must be in assembly/index.ts or re-exported from it
@inline decorator for hot-path functions (CPU tick, PPU tick)

Adding a New Export

Implement in the relevant module (e.g. assembly/audio/apu.ts)
Export from assembly/index.ts: export { myFunction } from "./audio/apu"
Rebuild: pnpm run asbuild:debug
TypeScript types auto-update in build/backend.d.ts
Import in frontend: import { myFunction } from "../build/backend"

Timing Reference

CPU: 4,194,162 Hz — each CPU.Tick() advances 1 M-cycle (4 T-cycles)
PPU: 456 M-cycles per scanline, 154 scanlines per frame → ~69,903 cycles/frame
Audio: 44,100 Hz sample rate; APU writes samples into double-buffered output

Running Tests

pnpm test                    # all suites
# Individual suites called via testCpu(), testVideo(), etc. (also WASM exports)

$ARGUMENTS

---name: backenddescription: Prime context for working on the AssemblyScript/WASM GameBoy emulator backend in /assembly/---You are working on the **AssemblyScript backend** of SvelteBoy, a GameBoy DMG emulator that compiles to WebAssembly.## Key Facts- Language: **AssemblyScript** (TypeScript-like, compiles to WASM via `asc`)- Entry point / public API: `assembly/index.ts` — all exports must be declared here- Main loop: `assembly/emulator.ts` — `Emulator.Run()` ticks CPU, Timer, PPU, DMA each cycle- Build: `pnpm run asbuild:debug` (dev) or `pnpm run asbuild:release` (prod)- Output: `build/backend.wasm` + `build/backend.js` (auto-generated ESM bindings)- Tests: `pnpm test` — runs suites in `assembly/tests/`## Module Map| Area | Path | Key files ||------|------|-----------|| CPU | `assembly/cpu/` | `cpu.ts` (registers/state), `opcodes.ts` (256+256 CB-prefix decode), `alu.ts`, `interrupts.ts` || PPU | `assembly/io/video/` | `ppu.ts` (main renderer), `scanlineRenderer.ts`, `pixelFifo.ts`, `oam.ts`, `dma.ts` || APU | `assembly/audio/` | `apu.ts` (core), `render.ts` (sample gen), `PulseChannel.ts`, `WaveChannel.ts`, `NoiseChannel.ts` || Memory | `assembly/memory/` | `memoryMap.ts` (address dispatch), `mbc1/2/3.ts` (bank controllers), `savegame.ts` || I/O | `assembly/io/` | `joypad.ts` (input), `timer.ts` (DIV/TIMA), `serial.ts` || Debug | `assembly/debug/` | `debugger.ts` (breakpoints), `debugInfo.ts` (snapshots), `disassemble.ts` |## WASM Memory Layout (linear, flat)```0x00000000 VRAM (16KB)0x00004000 OAM (160B)0x000040A0 Ext RAM (512KB, cartridge)0x000840A0 Work RAM (32KB)0x0010C0A0 I/O Regs (128B)0x0010C120 High RAM (128B)0x0010CBA4 Cart ROM (up to 8MB)```## AssemblyScript Gotchas- No closures capturing `this` — use module-level functions or static class methods- Typed arrays are value types: `Uint8Array`, `Int16Array`, etc. are first-class- `memory.data<u8>(offset)` for direct memory reads; use `store<u8>(ptr, val)` / `load<u8>(ptr)` for raw access- No `Map`/`Set` generics with reference types — use `StaticArray` or custom structures- Exported functions must be in `assembly/index.ts` or re-exported from it- `@inline` decorator for hot-path functions (CPU tick, PPU tick)## Adding a New Export1. Implement in the relevant module (e.g. `assembly/audio/apu.ts`)2. Export from `assembly/index.ts`: `export { myFunction } from "./audio/apu"`3. Rebuild: `pnpm run asbuild:debug`4. TypeScript types auto-update in `build/backend.d.ts`5. Import in frontend: `import { myFunction } from "../build/backend"`## Timing Reference- CPU: 4,194,162 Hz — each `CPU.Tick()` advances 1 M-cycle (4 T-cycles)- PPU: 456 M-cycles per scanline, 154 scanlines per frame → ~69,903 cycles/frame- Audio: 44,100 Hz sample rate; APU writes samples into double-buffered output## Running Tests```bashpnpm test # all suites# Individual suites called via testCpu(), testVideo(), etc. (also WASM exports)```$ARGUMENTS

Frequently asked questions

Backend