v86: defer V86-mode VBE disable; add DOS-box probe scenario (#359)

Rebuilds libv86.js from felixrieseberg/v86@windows95-base, which now
carries vga-defer-vbe-disable-v86: when a windowed DOS VM's vgabios
writes dispi[4]=0, Win9x's VDD passes that through (it doesn't know
about ports 1CE/1CF) while virtualising the rest of the mode-set, so
v86 used to drop out of LFB rendering with the legacy registers still
holding SVGA values and the screen turned to planar garbage. The fix
defers the disable until a legacy attribute-mode write actually
reaches the hardware.

debug-harness: WIN95_PROBE_DOSBOX=1 opens command from Run, types
dir, optionally Alt+Enters (WIN95_PROBE_DOSBOX_ALTENTER=1).
WIN95_PROBE_VGATRACE=1 wraps the VGA io.ports[] entries (not the
VGAScreen methods, which are captured by-value at registration) and
dumps [port, op, value, eip+VM/PE/CPL] tuples to
/tmp/win95-vgatrace.json — that EIP/mode column is what pinned the
leak on V86-mode vgabios at C000:2C8x.

.claude/skills/probe-win95/SKILL.md

@@ -37,7 +37,13 @@ WIN95_SMB_SHARE="$HOME/Downloads" \
 ```
 
 `WIN95_PROBE_SCRIPT='HOST/HOST'` types `\\HOST\HOST` into Start → Run on
-desktop. `/` → `\` substitution (env var / shell quoting, pragmatism). The
+desktop. `WIN95_PROBE_DOSBOX=1` instead opens `command`, types `dir`,
+and (with `WIN95_PROBE_DOSBOX_ALTENTER=1`) toggles fullscreen — this is
+the regression scenario for the windowed-DOS-box VBE leak.
+`WIN95_PROBE_VGATRACE=1` wraps the VGA I/O ports at the `io.ports[]`
+layer and writes `[port, op, value, "eip VMPE cplN"]` tuples to
+`/tmp/win95-vgatrace.json` every tick (heavy — can hit 1M entries during
+boot). `/` → `\` substitution (env var / shell quoting, pragmatism). The
 harness drives it via XT scancodes — Win95 doesn't have Win+R (Win98+
 only), so the sequence is Esc, Esc, Ctrl+Esc, R, backslashes + text,
 Enter.

.claude/skills/update-v86/SKILL.md

@@ -23,7 +23,7 @@ fallbacks, no fetching from copy.sh.
 ## The fork branch
 
 v86 should be checked out on **`felixrieseberg/v86:windows95-base`**.
-That branch merges three feature branches, each upstreamable on its own:
+That branch merges four feature branches, each upstreamable on its own:
 
 - **`electron-renderer-fs-loader`** (PR #1540) — `src/lib.js` uses
   `require("fs")` instead of `await import("node:fs/promises")`. Dynamic
@@ -40,6 +40,13 @@ That branch merges three feature branches, each upstreamable on its own:
   (VBADOS VBMOUSE) can read absolute cursor position and track the host
   cursor 1:1 without pointer lock. Consumes the `mouse-absolute` bus
   event that `MouseAdapter` already emits.
+- **`vga-defer-vbe-disable-v86`** — `src/vga.js` defers `dispi[4]=0`
+  written from V86 mode until a legacy attribute-mode write reaches the
+  hardware. Win9x's VDD virtualises ports 3B0–3DF for a windowed DOS VM
+  but not 1CE/1CF, so vgabios's VBE-disable leaks through while the rest
+  of its mode-set is captured into the VM's virtual register file —
+  without this the screen turns to planar garbage the moment you open a
+  DOS box.
 
 ## Prerequisites
 

src/renderer/debug-harness.ts

@@ -36,8 +36,78 @@ const SC = {
   R_DN: [0x13], R_UP: [0x93],
   ENTER_DN: [0x1c], ENTER_UP: [0x9c],
   BACKSLASH_DN: [0x2b], BACKSLASH_UP: [0xab],
+  ALT_DN: [0x38], ALT_UP: [0xb8],
 };
 
+// WIN95_PROBE_VGATRACE=1 → wrap VGA I/O ports at the io.ports[] layer (the
+// VGAScreen.portXXX_write methods are captured by-value at registration time,
+// so monkey-patching them on the instance is a no-op for most ports). Each
+// entry is [port, op, value, "eip VMPE cplN"] so you can tell vgabios in V86
+// mode apart from the ring-0 display driver.
+const VGATRACE_FILE = "/tmp/win95-vgatrace.json";
+let vgaTrace: any[] | undefined;
+
+function armVgaTrace(emulator: any) {
+  const cpu = emulator.v86?.cpu;
+  const io = cpu?.io;
+  if (!io || vgaTrace) return;
+  vgaTrace = [];
+  const ctx = () => {
+    try {
+      const ip = (cpu.instruction_pointer[0] >>> 0).toString(16);
+      const vm = cpu.flags[0] & (1 << 17) ? "VM" : "  ";
+      const pe = cpu.cr[0] & 1 ? "PE" : "  ";
+      return `${ip} ${vm}${pe} cpl${cpu.cpl[0]}`;
+    } catch { return "?"; }
+  };
+  const W = [0x3c0, 0x3c2, 0x3c4, 0x3c5, 0x3ce, 0x3cf, 0x3d4, 0x3d5, 0x3b4, 0x3b5, 0x1ce, 0x1cf];
+  const R = [0x1cf, 0x3da, 0x3c1];
+  for (const p of W) for (const w of ["write8", "write16"]) {
+    const orig = io.ports[p][w];
+    io.ports[p][w] = function (v: number) {
+      vgaTrace!.push([p, w, v, ctx()]);
+      return orig.call(this, v);
+    };
+  }
+  for (const p of R) for (const r of ["read8", "read16"]) {
+    const orig = io.ports[p][r];
+    io.ports[p][r] = function () {
+      const v = orig.call(this);
+      vgaTrace!.push([p, r, v, ctx()]);
+      return v;
+    };
+  }
+  console.log("[probe] vga trace armed");
+}
+
+function dumpVgaTrace(emulator: any) {
+  if (!vgaTrace) return;
+  const d = emulator.v86?.cpu?.devices?.vga;
+  const state = d && {
+    svga_enabled: d.svga_enabled,
+    graphical_mode: d.graphical_mode,
+    attribute_mode: d.attribute_mode,
+    miscellaneous_graphics_register: d.miscellaneous_graphics_register,
+    sequencer_memory_mode: d.sequencer_memory_mode,
+    clocking_mode: d.clocking_mode,
+    plane_write_bm: d.plane_write_bm,
+    crtc_mode: d.crtc_mode,
+    max_scan_line: d.max_scan_line,
+    underline_location_register: d.underline_location_register,
+    horizontal_display_enable_end: d.horizontal_display_enable_end,
+    horizontal_blank_start: d.horizontal_blank_start,
+    vertical_display_enable_end: d.vertical_display_enable_end,
+    vertical_blank_start: d.vertical_blank_start,
+    offset_register: d.offset_register,
+    dispi_enable_value: d.dispi_enable_value,
+    screen_width: d.screen_width,
+    screen_height: d.screen_height,
+    max_cols: d.max_cols,
+    max_rows: d.max_rows,
+  };
+  fs.writeFileSync(VGATRACE_FILE, JSON.stringify({ state, trace: vgaTrace }));
+}
+
 function sendChord(emu: any, ...keys: { dn: number[]; up: number[] }[]) {
   for (const k of keys) emu.keyboard_send_scancodes(k.dn);
   setTimeout(() => {
@@ -80,10 +150,16 @@ export function startProbe(emulator: any) {
   // Enter, then optional WIN95_PROBE_RUN_AFTER keystrokes after _RUN_WAIT ms.
   const runCmd = process.env.WIN95_PROBE_RUN;
   const runAfter = process.env.WIN95_PROBE_RUN_AFTER;
-  let scriptArmed = !!scriptCmd || !!runCmd;
+  // WIN95_PROBE_DOSBOX=1 → after desktop, open COMMAND.COM, type `dir`,
+  // optionally Alt+Enter to fullscreen. Regression test for the windowed
+  // DOS box clobbering VBE (felixrieseberg/v86 vga-defer-vbe-disable-v86).
+  const dosBox = process.env.WIN95_PROBE_DOSBOX === "1";
+  const wantVgaTrace = process.env.WIN95_PROBE_VGATRACE === "1";
+  let scriptArmed = !!scriptCmd || !!runCmd || dosBox;
 
   const tick = () => {
     try {
+      if (wantVgaTrace && !vgaTrace) armVgaTrace(emulator);
       const s = collectStatus(emulator);
       fs.writeFileSync(STATUS_FILE, JSON.stringify(s, null, 2));
 
@@ -98,11 +174,46 @@ export function startProbe(emulator: any) {
         }
       } catch {}
 
+      dumpVgaTrace(emulator);
+
       // Once at desktop, fire the keyboard script (once). The 8s settle is
       // for the "Welcome to Windows 95" tip dialog to be dismissable —
       // we send Esc first to clear it.
       if (scriptArmed && s.phase === "desktop" && s.uptimeSec > 8) {
         scriptArmed = false;
+        if (dosBox) {
+          console.log("[probe] desktop detected, opening DOS box");
+          runScript(emulator, [
+            { type: "wait", ms: 3000 },
+            { type: "keys", dn: SC.ESC_DN, up: SC.ESC_UP },
+            { type: "wait", ms: 1000 },
+            { type: "keys", dn: SC.ESC_DN, up: SC.ESC_UP },
+            { type: "wait", ms: 1000 },
+            { type: "chord", keys: [
+              { dn: SC.CTRL_DN, up: SC.CTRL_UP },
+              { dn: SC.ESC_DN, up: SC.ESC_UP },
+            ]},
+            { type: "wait", ms: 1200 },
+            { type: "keys", dn: SC.R_DN, up: SC.R_UP },
+            { type: "wait", ms: 1000 },
+            { type: "text", text: "command" },
+            { type: "wait", ms: 400 },
+            { type: "keys", dn: SC.ENTER_DN, up: SC.ENTER_UP },
+            { type: "wait", ms: 5000 },
+            { type: "text", text: "dir" },
+            { type: "wait", ms: 200 },
+            { type: "keys", dn: SC.ENTER_DN, up: SC.ENTER_UP },
+            { type: "wait", ms: 3000 },
+            ...(process.env.WIN95_PROBE_DOSBOX_ALTENTER === "1" ? [
+              { type: "chord", keys: [
+                { dn: SC.ALT_DN, up: SC.ALT_UP },
+                { dn: SC.ENTER_DN, up: SC.ENTER_UP },
+              ]},
+              { type: "wait", ms: 4000 },
+            ] : []),
+          ]);
+          return;
+        }
         if (runCmd) {
           console.log("[probe] desktop detected, Run →", runCmd);
           runScript(emulator, [
@@ -128,7 +239,8 @@ export function startProbe(emulator: any) {
               { type: "keys", dn: SC.ENTER_DN, up: SC.ENTER_UP },
             ] : []),
           ]);
-        } else {
+          return;
+        }
         console.log("[probe] desktop detected, running script:", scriptCmd);
         runScript(emulator, [
           { type: "wait", ms: 3000 },
@@ -160,7 +272,6 @@ export function startProbe(emulator: any) {
           { type: "wait", ms: 400 },
           { type: "keys", dn: SC.ENTER_DN, up: SC.ENTER_UP },
         ]);
-        }
       }
 
       if (s.verdict) {
@@ -273,7 +384,7 @@ function collectStatus(emulator: any): ProbeStatus {
   // Made it to ≥640×480 graphics → desktop reached. But if a keyboard
   // script is running, hold off — the outer harness reads the SMB log
   // directly and we just keep the app alive.
-  else if (atDesktop && uptimeSec > 30 && !process.env.WIN95_PROBE_SCRIPT && !process.env.WIN95_PROBE_RUN) verdict = "SUCCESS";
+  else if (atDesktop && uptimeSec > 30 && !process.env.WIN95_PROBE_SCRIPT && !process.env.WIN95_PROBE_RUN && !process.env.WIN95_PROBE_DOSBOX) verdict = "SUCCESS";
   // Timeout
   else if (uptimeSec > 180) verdict = "FAIL_OTHER";
 

src/renderer/lib/libv86.js

@@ -426,11 +426,13 @@ this.mouse_clicks=this.mouse_delta_x=this.mouse_delta_y=0;break;case 245:this.en
 0;break;default:y(a)}this.mouse_irq()}}else if(this.read_controller_output_port)this.read_controller_output_port=!1,this.controller_output_port=a;else{y(a);this.mouse_buffer.clear();this.kbd_buffer.clear();this.kbd_buffer.push(250);switch(a){case 237:this.next_read_led=!0;break;case 240:this.next_handle_scan_code_set=!0;break;case 242:this.kbd_buffer.push(171);this.kbd_buffer.push(131);break;case 243:this.next_read_rate=!0;break;case 244:this.enable_keyboard_stream=!0;break;case 245:this.enable_keyboard_stream=
 !1;break;case 246:break;case 255:this.kbd_buffer.clear();this.kbd_buffer.push(250);this.kbd_buffer.push(170);this.kbd_buffer.push(0);break;default:y(a)}this.kbd_irq()}};
 Gc.prototype.port64_write=function(a){y(a);switch(a){case 32:this.kbd_buffer.clear();this.mouse_buffer.clear();this.kbd_buffer.push(this.command_register);this.kbd_irq();break;case 96:this.read_command_register=!0;break;case 209:this.read_controller_output_port=!0;break;case 211:this.read_output_register=!0;break;case 212:this.next_is_mouse_command=!0;break;case 167:this.command_register|=32;break;case 168:this.command_register&=-33;break;case 169:this.kbd_buffer.clear();this.mouse_buffer.clear();
-this.kbd_buffer.push(0);this.kbd_irq();break;case 170:this.kbd_buffer.clear();this.mouse_buffer.clear();this.kbd_buffer.push(85);this.kbd_irq();break;case 171:this.kbd_buffer.clear();this.mouse_buffer.clear();this.kbd_buffer.push(0);this.kbd_irq();break;case 173:this.command_register|=16;break;case 174:this.command_register&=-17;break;case 254:this.cpu.reboot_internal();break;default:y(a)}};function Hc(a,b){this.cpu=a;this.bus=b;this.absolute=this.enabled=!1;this.queue=[];this.buttons=0;this.last_y=this.last_x=-1;this.tail_is_move=!1;this.bus.register("mouse-absolute",function(c){const d=Math.max(0,Math.min(65535,Math.round(c[0]/c[2]*65535)));c=Math.max(0,Math.min(65535,Math.round(c[1]/c[3]*65535)));if(d!==this.last_x||c!==this.last_y)this.last_x=d,this.last_y=c,this.push_packet(0,!0)},this);this.bus.register("mouse-click",function(c){this.buttons=(c[0]?32:0)|(c[1]?8:0)|(c[2]?16:0);
+this.kbd_buffer.push(0);this.kbd_irq();break;case 170:this.kbd_buffer.clear();this.mouse_buffer.clear();this.kbd_buffer.push(85);this.kbd_irq();break;case 171:this.kbd_buffer.clear();this.mouse_buffer.clear();this.kbd_buffer.push(0);this.kbd_irq();break;case 173:this.command_register|=16;break;case 174:this.command_register&=-17;break;case 254:this.cpu.reboot_internal();break;default:y(a)}};function Hc(a,b){this.cpu=a;this.bus=b;this.absolute=this.enabled=!1;this.queue=[];this.buttons=0;this.last_y=this.last_x=-1;this.tail_is_move=!1;this.clip_out=new Uint8Array(0);this.clip_out_cursor=0;this.clip_out_fresh=!1;this.clip_in=new Uint8Array(0);this.clip_in_cursor=0;this.bus.register("vmware-clipboard-host",function(c){this.clip_out=65536<c.length?c.subarray(0,65536):c;this.clip_out_cursor=0;this.clip_out_fresh=!0},this);this.bus.register("mouse-absolute",function(c){const d=Math.max(0,
-this.push_packet(0,!1)},this);this.bus.register("mouse-wheel",function(c){this.push_packet(-c[0]|0,!1)},this);a.io.register_read(22104,this,void 0,void 0,this.port_read32);a.io.register_write(22104,this,void 0,void 0,this.port_write32)}
+Math.min(65535,Math.round(c[0]/c[2]*65535)));c=Math.max(0,Math.min(65535,Math.round(c[1]/c[3]*65535)));if(d!==this.last_x||c!==this.last_y)this.last_x=d,this.last_y=c,this.push_packet(0,!0)},this);this.bus.register("mouse-click",function(c){this.buttons=(c[0]?32:0)|(c[1]?8:0)|(c[2]?16:0);this.push_packet(0,!1)},this);this.bus.register("mouse-wheel",function(c){this.push_packet(-c[0]|0,!1)},this);a.io.register_read(22104,this,void 0,void 0,this.port_read32);a.io.register_write(22104,this,void 0,void 0,
-Hc.prototype.push_packet=function(a,b){!this.enabled||!this.absolute||0>this.last_x||(b&&this.tail_is_move&&4<=this.queue.length?(this.queue[this.queue.length-3]=this.last_x,this.queue[this.queue.length-2]=this.last_y):1024<this.queue.length+4?(this.enabled=!1,this.queue.length=0):(this.queue.push(this.buttons,this.last_x,this.last_y,a),this.tail_is_move=b))};
+this.port_write32)}Hc.prototype.push_packet=function(a,b){!this.enabled||!this.absolute||0>this.last_x||(b&&this.tail_is_move&&4<=this.queue.length?(this.queue[this.queue.length-3]=this.last_x,this.queue[this.queue.length-2]=this.last_y):1024<this.queue.length+4?(this.enabled=!1,this.queue.length=0):(this.queue.push(this.buttons,this.last_x,this.last_y,a),this.tail_is_move=b))};
-Hc.prototype.port_read32=function(){const a=this.cpu.reg32;if(1447909480!==(a[0]|0))return-1;switch(a[1]&65535){case 10:return a[3]=1447909480,6;case 40:return this.enabled?this.queue.length:-65536;case 39:const b=Math.min(a[3]>>>0,4,this.queue.length),c=[0,0,0,0];for(let d=0;d<b;d++)c[d]=this.queue.shift();a[3]=c[1];a[1]=c[2];a[2]=c[3];return c[0];case 41:switch(a[3]|0){case 1161905490:this.enabled=!0;this.queue.length=0;this.tail_is_move=!1;this.queue.push(876762442);break;case 245:this.absolute=
+Hc.prototype.port_read32=function(){var a=this.cpu.reg32;if(1447909480!==(a[0]|0))return-1;switch(a[1]&65535){case 10:return a[3]=1447909480,6;case 6:if(!this.clip_out_fresh)break;this.clip_out_fresh=!1;this.clip_out_cursor=0;return this.clip_out.length;case 7:var b=this.clip_out;a=this.clip_out_cursor;b=b[a]|0|(b[a+1]|0)<<8|(b[a+2]|0)<<16|(b[a+3]|0)<<24;this.clip_out_cursor=a+4;return b;case 8:return a=Math.min(a[3]>>>0,65536),this.clip_in=new Uint8Array(a),this.clip_in_cursor=0,0===a&&this.bus.send("vmware-clipboard-guest",
-this.enabled=!1;this.queue.length=0;this.bus.send("vmware-absolute-mouse",!1);break;case 1396851026:this.absolute=!0;this.bus.send("vmware-absolute-mouse",!0);break;case 1279611474:this.absolute=!1,this.bus.send("vmware-absolute-mouse",!1)}return 0}return-1};Hc.prototype.port_write32=function(){};Hc.prototype.get_state=function(){return[this.enabled,this.absolute]};Hc.prototype.set_state=function(a){this.enabled=a[0];this.absolute=a[1];this.bus.send("vmware-absolute-mouse",this.absolute)};const Ic=DataView.prototype,Jc={size:1,get:Ic.getUint8,set:Ic.setUint8},Kc={size:2,get:Ic.getUint16,set:Ic.setUint16},U={size:4,get:Ic.getUint32,set:Ic.setUint32},Mc=Lc([{magic:U},{class:Jc},{data:Jc},{version0:Jc},{osabi:Jc},{abiversion:Jc},{pad0:function(a){return{size:a,get:()=>-1}}(7)},{type:Kc},{machine:Kc},{version1:U},{entry:U},{phoff:U},{shoff:U},{flags:U},{ehsize:Kc},{phentsize:Kc},{phnum:Kc},{shentsize:Kc},{shnum:Kc},{shstrndx:Kc}]);console.assert(52===Mc.reduce((a,b)=>a+b.size,0));
+this.clip_in),0;case 9:b=this.clip_in;a=a[3]>>>0;var c=this.clip_in_cursor;c<b.length&&(b[c++]=a);c<b.length&&(b[c++]=a>>>8);c<b.length&&(b[c++]=a>>>16);c<b.length&&(b[c++]=a>>>24);this.clip_in_cursor=c;c>=b.length&&(this.bus.send("vmware-clipboard-guest",b),this.clip_in=new Uint8Array(0),this.clip_in_cursor=0);return 0;case 40:return this.enabled?this.queue.length:-65536;case 39:b=Math.min(a[3]>>>0,4,this.queue.length);c=[0,0,0,0];for(let d=0;d<b;d++)c[d]=this.queue.shift();a[3]=c[1];a[1]=c[2];a[2]=
+c[3];return c[0];case 41:switch(a[3]|0){case 1161905490:this.enabled=!0;this.queue.length=0;this.tail_is_move=!1;this.queue.push(876762442);break;case 245:this.absolute=this.enabled=!1;this.queue.length=0;this.bus.send("vmware-absolute-mouse",!1);break;case 1396851026:this.absolute=!0;this.bus.send("vmware-absolute-mouse",!0);break;case 1279611474:this.absolute=!1,this.bus.send("vmware-absolute-mouse",!1)}return 0}return-1};Hc.prototype.port_write32=function(){};
+Hc.prototype.get_state=function(){return[this.enabled,this.absolute]};Hc.prototype.set_state=function(a){this.enabled=a[0];this.absolute=a[1];this.bus.send("vmware-absolute-mouse",this.absolute)};const Ic=DataView.prototype,Jc={size:1,get:Ic.getUint8,set:Ic.setUint8},Kc={size:2,get:Ic.getUint16,set:Ic.setUint16},U={size:4,get:Ic.getUint32,set:Ic.setUint32},Mc=Lc([{magic:U},{class:Jc},{data:Jc},{version0:Jc},{osabi:Jc},{abiversion:Jc},{pad0:function(a){return{size:a,get:()=>-1}}(7)},{type:Kc},{machine:Kc},{version1:U},{entry:U},{phoff:U},{shoff:U},{flags:U},{ehsize:Kc},{phentsize:Kc},{phnum:Kc},{shentsize:Kc},{shnum:Kc},{shstrndx:Kc}]);console.assert(52===Mc.reduce((a,b)=>a+b.size,0));
 const Nc=Lc([{type:U},{offset:U},{vaddr:U},{paddr:U},{filesz:U},{memsz:U},{flags:U},{align:U}]);console.assert(32===Nc.reduce((a,b)=>a+b.size,0));const Oc=Lc([{name:U},{type:U},{flags:U},{addr:U},{offset:U},{size:U},{link:U},{info:U},{addralign:U},{entsize:U}]);console.assert(40===Oc.reduce((a,b)=>a+b.size,0));function Lc(a){return a.map(function(b){var c=Object.keys(b);console.assert(1===c.length);c=c[0];b=b[c];console.assert(0<b.size);return{name:c,type:b,size:b.size,get:b.get,set:b.set}})}
 function Pc(a,b){const c={};let d=0;for(const e of b)b=e.get.call(a,d,!0),console.assert(void 0===c[e.name]),c[e.name]=b,d+=e.size;return[c,d]}function Qc(a,b,c){const d=[];let e=0;for(var f=0;f<c;f++){const [g,h]=Pc(new DataView(a.buffer,a.byteOffset+e,void 0),b);d.push(g);e+=h}return[d,e]};const Rc={[0]:0,[1]:525,[2]:525,[3]:350,[4]:350,[5]:350};
 function V(a,b,c,d){this.io=a.io;this.cpu=a;this.dma=a.devices.dma;this.cmd_table=this.build_cmd_lookup_table();this.sra=0;this.srb=192;this.dor=12;this.tdr=0;this.msr=128;this.dsr=0;this.cmd_phase=1;this.cmd_flags=this.cmd_code=0;this.cmd_buffer=new Uint8Array(17);this.cmd_remaining=this.cmd_cursor=0;this.response_data=new Uint8Array(15);this.reset_sense_int_count=this.curr_drive_no=this.status1=this.status0=this.response_length=this.response_cursor=0;this.locked=!1;this.head_load_time=this.step_rate_interval=
@@ -587,8 +589,8 @@ X.prototype.update_layers=function(){this.graphical_mode||this.text_mode_redraw(
 d=Math.min(d,this.screen_height);var f=this.screen_height-d;this.layers=[];e=-e;for(var g=0;e<this.screen_width;e+=this.virtual_width,g++)this.layers.push({image_data:this.image_data,screen_x:e,screen_y:0,buffer_x:0,buffer_y:a+g,buffer_width:this.virtual_width,buffer_height:d});a=0;this.attribute_mode&32||(a=this.vga_addr_to_pixel(c)+b);e=-a;for(g=0;e<this.screen_width;e+=this.virtual_width,g++)this.layers.push({image_data:this.image_data,screen_x:e,screen_y:d,buffer_x:0,buffer_y:g,buffer_width:this.virtual_width,
 buffer_height:f})}};X.prototype.update_vertical_retrace=function(){this.port_3DA_value|=8;this.start_address_latched!==this.start_address&&(this.start_address_latched=this.start_address,this.update_layers())};X.prototype.update_cursor_scanline=function(){var a=this.max_scan_line&31;const b=Math.min(a,this.cursor_scanline_start&31);a=Math.min(a,this.cursor_scanline_end&31);this.screen.update_cursor_scanline(b,a,!(this.cursor_scanline_start&32)&&b<a)};
 X.prototype.port3C0_write=function(a){if(-1===this.attribute_controller_index)y(a),this.attribute_controller_index=a&31,y(this.attribute_controller_index),this.palette_source!==(a&32)&&(this.palette_source=a&32,this.update_layers());else{if(16>this.attribute_controller_index)y(this.attribute_controller_index),y(a),this.dac_map[this.attribute_controller_index]=a,this.attribute_mode&64||this.complete_redraw();else switch(this.attribute_controller_index){case 16:y(a);if(this.attribute_mode!==a){var b=
-this.attribute_mode;this.attribute_mode=a;const c=0!==(a&1);this.svga_enabled||this.graphical_mode===c||(this.graphical_mode=c,this.screen.set_mode(this.graphical_mode));(b^a)&64&&this.complete_replot();this.update_vga_size();this.complete_redraw();this.set_font_bitmap(!1)}break;case 18:y(a);this.color_plane_enable!==a&&(this.color_plane_enable=a,this.complete_redraw());break;case 19:y(a);this.horizontal_panning!==a&&(this.horizontal_panning=a&15,this.update_layers());break;case 20:y(a);this.color_select!==
+this.attribute_mode;this.attribute_mode=a;!this.svga_enabled||this.dispi_enable_value&1||(this.svga_enabled=!1,this.svga_bank_offset=0);const c=0!==(a&1);this.svga_enabled||this.graphical_mode===c||(this.graphical_mode=c,this.screen.set_mode(this.graphical_mode));(b^a)&64&&this.complete_replot();this.update_vga_size();this.complete_redraw();this.set_font_bitmap(!1)}break;case 18:y(a);this.color_plane_enable!==a&&(this.color_plane_enable=a,this.complete_redraw());break;case 19:y(a);this.horizontal_panning!==
-a&&(this.color_select=a,this.complete_redraw());break;default:y(this.attribute_controller_index),y(a)}this.attribute_controller_index=-1}};X.prototype.port3C0_read=function(){return(this.attribute_controller_index|this.palette_source)&255};X.prototype.port3C0_read16=function(){return this.port3C0_read()|this.port3C1_read()<<8&65280};
+a&&(this.horizontal_panning=a&15,this.update_layers());break;case 20:y(a);this.color_select!==a&&(this.color_select=a,this.complete_redraw());break;default:y(this.attribute_controller_index),y(a)}this.attribute_controller_index=-1}};X.prototype.port3C0_read=function(){return(this.attribute_controller_index|this.palette_source)&255};X.prototype.port3C0_read16=function(){return this.port3C0_read()|this.port3C1_read()<<8&65280};
 X.prototype.port3C1_read=function(){if(16>this.attribute_controller_index)return y(this.attribute_controller_index),y(this.dac_map[this.attribute_controller_index]),this.dac_map[this.attribute_controller_index]&255;switch(this.attribute_controller_index){case 16:return y(this.attribute_mode),this.attribute_mode;case 18:return y(this.color_plane_enable),this.color_plane_enable;case 19:return y(this.horizontal_panning),this.horizontal_panning;case 20:return y(this.color_select),this.color_select;default:y(this.attribute_controller_index)}return 255};
 X.prototype.port3C2_write=function(a){y(a);this.miscellaneous_output_register=a};X.prototype.port3C4_write=function(a){this.sequencer_index=a};X.prototype.port3C4_read=function(){return this.sequencer_index};
 X.prototype.port3C5_write=function(a){switch(this.sequencer_index){case 1:y(a);var b=this.clocking_mode;this.clocking_mode=a;(b^a)&32&&this.update_layers();this.set_font_bitmap(!1);break;case 2:y(a);b=this.plane_write_bm;this.plane_write_bm=a;this.graphical_mode||!(b&4)||this.plane_write_bm&4||this.set_font_bitmap(!0);break;case 3:y(a);b=this.character_map_select;this.character_map_select=a;this.graphical_mode||b===a||this.set_font_page();break;case 4:y(a);this.sequencer_memory_mode=a;break;default:y(this.sequencer_index),
@@ -608,9 +610,10 @@ a,this.update_vga_size(),(b^a)&67&&this.complete_replot());break;case 24:y(a);th
 X.prototype.port3D5_read=function(){y(this.index_crtc);switch(this.index_crtc){case 1:return this.horizontal_display_enable_end;case 2:return this.horizontal_blank_start;case 7:return this.vertical_display_enable_end>>7&2|this.vertical_blank_start>>5&8|this.line_compare>>4&16|this.vertical_display_enable_end>>3&64;case 8:return this.preset_row_scan;case 9:return this.max_scan_line;case 10:return this.cursor_scanline_start;case 11:return this.cursor_scanline_end;case 12:return this.start_address&255;
 case 13:return this.start_address>>8;case 14:return this.cursor_address>>8;case 15:return this.cursor_address&255;case 18:return this.vertical_display_enable_end&255;case 19:return this.offset_register;case 20:return this.underline_location_register;case 21:return this.vertical_blank_start&255;case 23:return this.crtc_mode;case 24:return this.line_compare&255}return this.index_crtc<this.crtc.length?this.crtc[this.index_crtc]:0};X.prototype.port3D5_read16=function(){return this.port3D5_read()};
 X.prototype.port3DA_read=function(){var a=this.port_3DA_value;this.graphical_mode?(this.port_3DA_value^=1,this.port_3DA_value&=1):(this.port_3DA_value&1&&(this.port_3DA_value^=8),this.port_3DA_value^=1);this.attribute_controller_index=-1;return a};X.prototype.port1CE_write=function(a){this.dispi_index=a};
-X.prototype.port1CF_write=function(a){y(this.dispi_index);y(a);const b=this.svga_enabled;switch(this.dispi_index){case 0:45248<=a&&45253>=a?this.svga_version=a:y(a);break;case 1:this.svga_width=a;2560<this.svga_width&&(this.svga_width=2560);break;case 2:this.svga_height=a;1600<this.svga_height&&(this.svga_height=1600);break;case 3:this.svga_bpp=a;break;case 4:(this.svga_enabled=1===(a&1))&&0===(a&128)&&this.svga_memory.fill(0);this.dispi_enable_value=a;break;case 5:y(a<<16);this.svga_bank_offset=
+X.prototype.port1CF_write=function(a){y(this.dispi_index);y(a);const b=this.svga_enabled;switch(this.dispi_index){case 0:45248<=a&&45253>=a?this.svga_version=a:y(a);break;case 1:this.svga_width=a;2560<this.svga_width&&(this.svga_width=2560);break;case 2:this.svga_height=a;1600<this.svga_height&&(this.svga_height=1600);break;case 3:this.svga_bpp=a;break;case 4:if(!(a&1)&&this.svga_enabled&&this.cpu.flags[0]&131072){this.dispi_enable_value=a;break}(this.svga_enabled=1===(a&1))&&0===(a&128)&&this.svga_memory.fill(0);
-a<<16;break;case 8:y(a);this.svga_offset_x!==a&&(this.svga_offset_x=a,this.svga_offset=this.svga_offset_y*this.svga_width+this.svga_offset_x,this.complete_redraw());break;case 9:y(a*this.svga_width);y(a);this.svga_offset_y!==a&&(this.svga_offset_y=a,this.svga_offset=this.svga_offset_y*this.svga_width+this.svga_offset_x,this.complete_redraw());break;default:y(this.dispi_index)}!this.svga_enabled||this.svga_width&&this.svga_height||(this.svga_enabled=!1);this.svga_enabled&&!b&&(this.svga_offset_y=this.svga_offset_x=
+this.dispi_enable_value=a;break;case 5:y(a<<16);this.svga_bank_offset=a<<16;break;case 8:y(a);this.svga_offset_x!==a&&(this.svga_offset_x=a,this.svga_offset=this.svga_offset_y*this.svga_width+this.svga_offset_x,this.complete_redraw());break;case 9:y(a*this.svga_width);y(a);this.svga_offset_y!==a&&(this.svga_offset_y=a,this.svga_offset=this.svga_offset_y*this.svga_width+this.svga_offset_x,this.complete_redraw());break;default:y(this.dispi_index)}!this.svga_enabled||this.svga_width&&this.svga_height||
-this.svga_offset=0,this.graphical_mode=!0,this.screen.set_mode(this.graphical_mode),this.set_size_graphical(this.svga_width,this.svga_height,this.svga_width,this.svga_height,this.svga_bpp));b&&!this.svga_enabled&&(this.graphical_mode=a=0!==(this.attribute_mode&1),this.screen.set_mode(a),this.update_vga_size(),this.set_font_bitmap(!1),this.complete_redraw());this.svga_enabled||(this.svga_bank_offset=0);this.update_layers()};X.prototype.port1CF_read=function(){y(this.dispi_index);return this.svga_register_read(this.dispi_index)};
+(this.svga_enabled=!1);this.svga_enabled&&4===this.dispi_index&&(b||(this.svga_offset_y=this.svga_offset_x=this.svga_offset=0),this.graphical_mode=!0,this.screen.set_mode(this.graphical_mode),this.set_size_graphical(this.svga_width,this.svga_height,this.svga_width,this.svga_height,this.svga_bpp));b&&!this.svga_enabled&&(this.graphical_mode=a=0!==(this.attribute_mode&1),this.screen.set_mode(a),this.update_vga_size(),this.set_font_bitmap(!1),this.complete_redraw());this.svga_enabled||(this.svga_bank_offset=
+0);this.update_layers()};X.prototype.port1CF_read=function(){y(this.dispi_index);return this.svga_register_read(this.dispi_index)};
 X.prototype.svga_register_read=function(a){switch(a){case 0:return this.svga_version;case 1:return this.dispi_enable_value&2?2560:this.svga_width;case 2:return this.dispi_enable_value&2?1600:this.svga_height;case 3:return this.dispi_enable_value&2?32:this.svga_bpp;case 4:return this.dispi_enable_value;case 5:return this.svga_bank_offset>>>16;case 6:return this.screen_width?this.screen_width:1;case 8:return this.svga_offset_x;case 9:return this.svga_offset_y;case 10:return this.vga_memory_size/65536|
 0;default:y(this.dispi_index)}return 255};
 X.prototype.vga_replot=function(){for(var a=this.diff_plot_min&-16,b=Math.min(this.diff_plot_max|15,524287),c=this.vga_addr_shift_count(),d=~this.crtc_mode&3,e=this.planar_mode&96,f=this.attribute_mode&64;a<=b;){var g=a>>>c;if(d){var h=a/this.virtual_width|0,l=a-this.virtual_width*h;switch(d){case 1:g=(h&1)<<13;h>>>=1;break;case 2:g=(h&1)<<14;h>>>=1;break;case 3:g=(h&3)<<13,h>>>=2}g|=(h*this.virtual_width+l>>>c)+this.start_address}h=this.plane0[g];l=this.plane1[g];var m=this.plane2[g],n=this.plane3[g];