mirror of
https://github.com/sehugg/8bitworkshop.git
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266 lines
7.0 KiB
Markdown
266 lines
7.0 KiB
Markdown
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class Platform
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--------------
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Mandatory functions:
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~~~
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start() : void;
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reset() : void;
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isRunning() : boolean;
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pause() : void;
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resume() : void;
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loadROM(title:string, rom:any);
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~~~
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These are for the compiler/editor:
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~~~
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getToolForFilename(s:string) : string;
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getDefaultExtension() : string;
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getPresets() : Preset[];
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~~~
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Most platforms have these:
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~~~
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loadState?(state : EmuState) : void;
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saveState?() : EmuState;
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~~~
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... etc
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6502
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----
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`advance()` advances one frame.
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The basic idea: iterate through all the scanlines, run a bunch of CPU cycles per scanline.
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If we hit a breakpoint, exit the loop.
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~~~
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var debugCond = this.getDebugCallback();
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for (var sl=0; sl<262; sl++) {
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for (var i=0; i<cpuCyclesPerLine; i++) {
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if (debugCond && debugCond()) {
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debugCond = null;
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sl = 999;
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break;
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}
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clock++;
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cpu.clockPulse();
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}
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}
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~~~
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Hitting a breakpoint does a `saveState()` but debug info is better when the platform is stopped at the breakpoint instead of being allowed to continue.
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Some platforms like `vector` aren't scanline-based, they just have a target number of scanlines per frame (per 1/60 sec)
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The 6502 CPU core is usually a byte behind the current instruction at breakpoints.
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So when saving state we +1 the PC by calling `fixPC`.
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When loading state we have to -1 the PC, load state, then +1 the PC.
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~~~
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this.unfixPC(state.c);
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cpu.loadState(state.c);
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this.fixPC(state.c);
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~~~
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Z80
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---
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There's a `runCPU()` wrapper:
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~~~
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advance(novideo : boolean) {
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for (var sl=0; sl<scanlinesPerFrame; sl++) {
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drawScanline(pixels, sl);
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this.runCPU(cpu, cpuCyclesPerLine);
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}
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// NMI each frame
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if (interruptEnabled) { cpu.nonMaskableInterrupt(); }
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}
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~~~
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Atari 2600
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-----------
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8bitworkshop was originally VCS-only, Javatari.js was the first emulator it supported.
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It's a wonderful emulator, but it didn't have hooks for debugging.
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I had to hack it up quite a bit, and wasn't sure what I was doing.
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A lot of the debugging functions just pass-through to my hacked-up functions:
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~~~
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step() { Javatari.room.console.debugSingleStepCPUClock(); }
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stepBack() { Javatari.room.console.debugStepBackInstruction(); }
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runEval(evalfunc) { Javatari.room.console.debugEval(evalfunc); }
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~~~
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Even so, I decided to monkey-patch the `clockPulse()` function so that I could record frames:
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~~~
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Javatari.room.console.oldClockPulse = Javatari.room.console.clockPulse;
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Javatari.room.console.clockPulse = function() {
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self.updateRecorder();
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this.oldClockPulse();
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}
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~~~
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Eventually I'd like to make it more like the other platforms.
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8bitworkshop uses its CPU core for other 6502 platforms.
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BasicZ80ScanlinePlatform
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------------------------
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Can be used to easily build a Z80-based raster platform.
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Just have to fill out the following:
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~~~
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cpuFrequency : number;
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canvasWidth : number;
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numTotalScanlines : number;
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numVisibleScanlines : number;
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defaultROMSize : number;
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abstract newRAM() : Uint8Array;
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abstract newMembus() : MemoryBus;
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abstract newIOBus() : MemoryBus;
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abstract getVideoOptions() : {};
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abstract getKeyboardMap();
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abstract startScanline(sl : number) : void;
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abstract drawScanline(sl : number) : void;
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getRasterScanline() : number { return this.currentScanline; }
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getKeyboardFunction() { return null; }
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~~~
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NES
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---
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NES uses the JSNES emulator, which has a callback function after each frame.
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~~~
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this.nes = new jsnes.NES({
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onFrame: (frameBuffer : number[]) => {
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},
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onAudioSample: (left:number, right:number) => {
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},
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onStatusUpdate: function(s) {
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},
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});
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~~~
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We monkey-patch the code to add a debugging hook:
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~~~
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// insert debug hook
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this.nes.cpu._emulate = this.nes.cpu.emulate;
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this.nes.cpu.emulate = () => {
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var cycles = this.nes.cpu._emulate();
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this.evalDebugCondition();
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return cycles;
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}
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~~~
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NES was the first platform with an "illegal opcode" hard stop, so we added a special `EmuHalt` exception which causes a breakpoint:
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~~~
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this.nes.stop = () => {
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console.log(this.nes.cpu.toJSON());
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throw new EmuHalt("CPU STOPPED @ PC $" + hex(this.nes.cpu.REG_PC));
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};
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~~~
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MAME
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----
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The `BaseMAMEPlatform` class implements a MAME platform.
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You just have to pass it various parameters when starting, and tell it how to load the ROM file:
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~~~
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class ColecoVisionMAMEPlatform extends BaseMAMEPlatform implements Platform {
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start() {
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this.startModule(this.mainElement, {
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jsfile: 'mamecoleco.js',
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cfgfile: 'coleco.cfg',
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biosfile: 'coleco/313 10031-4005 73108a.u2',
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driver: 'coleco',
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width: 280 * 2,
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height: 216 * 2,
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romfn: '/emulator/cart.rom',
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romsize: 0x8000,
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preInit: function(_self) {
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},
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});
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}
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loadROM(title, data) {
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this.loadROMFile(data);
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this.loadRegion(":coleco_cart:rom", data);
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}
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getPresets() { return ColecoVision_PRESETS; }
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getToolForFilename = getToolForFilename_z80;
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getDefaultExtension() { return ".c"; };
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}
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~~~
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A lot of things are done via Lua scripting -- for example, loading a ROM requires we loop over the memory region and issue `rgn:write_u32` calls.
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It kinda-sorta works, except debugging isn't reliable because MAME [doesn't return from the event loop](https://github.com/mamedev/mame/issues/3649) at breakpoints.
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MAME platforms don't have state load/save either.
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Verilog
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--------
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The Verilog platform is the odd one out, since it has no fixed CPU as such.
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The `loadROM` function instead loads a JavaScript function.
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Some platforms do have a ROM if using assembly, so we load that into a Verilog array.
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It's quite the hack, and it could be better.
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Verilog has its own debugger, logging signals in a fixed-size buffer.
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Profiling
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----------
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`EmuProfilerImpl` runs the profiler.
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When started, it calls `setBreakpoint` to add a profiler-specific breakpoint that never hits, just records the CPU state at each clock.
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It uses `getRasterScanline` to associate IPs with scanlines.
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Platforms can also log their own reads, writes, interrupts, etc.
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Future Ideas
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------------
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There should be a standard CPU interface, buses, memory map.
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More like MAME configuration.
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Platforms might have different ideas of "clock" (CPU clock, pixel clock, 1 clock per instruction, etc)
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The goal is to rewind and advance to any clock cycle within a frame, and get complete introspection of events, without hurting performance.
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Unify raster platforms, they should all allow the same debugging and CPU interfaces.
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Separate UI/sim parts of platform?
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A lot of platforms write into a uint32 buffer.
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We might want to buffer audio the same way.
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Also some way to log events, and handle input.
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Figure out how to make platform-specific type for load/save state.
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(generics?)
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Separate emulators from 8bitworkshop IDE.
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Can we use WASM emulators without JS interop penalty?
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Maybe using [AssemblyScript](https://docs.assemblyscript.org/)?
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Startup would be faster, probably runtime too.
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Drawback is that dynamic stuff (custom breakpoint functions, profiling) might be slow, slower dev too maybe.
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Need proof-of-concept.
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