nes: fix write() bug

extension/docs/emulator.md

@@ -75,7 +75,7 @@ In a folder with a launch configuration, <kbd>F5</kbd> does the same, and
   of memory, `#mem16[addr]` for a word.
 - **Memory:** the binary-data icon next to a register or symbol opens
   memory at that address in the Hex Editor (VS Code offers to install
-  it). On most platforms you can edit it there; NES, VCS and MAME-based
+  it). On most platforms you can edit it there; VCS and MAME-based
   platforms are read-only.
 - **Disassembly:** right-click in the Call Stack and choose **Open
   Disassembly View**. It shows instructions with their symbols and source

extension/notes/PLAN.md

@@ -1871,8 +1871,9 @@ runs has to be a webview too.
 - **Memory writes.** `EmuCore.write()` goes through the machine's bus, so
   writing an I/O address does what a store there does. It restarts the
   timeline (the past can't be replayed into the edited state). It needs a
-  `Machine`, so NES (JSNES), VCS and the MAME platforms
-  can't write; `DebugCapabilities.write` says so and the adapter turns on
+  `Machine` with `write()`, so VCS and the MAME platforms can't write
+  (NES's `JSNESMachine` writes RAM or the mapper directly, skipping
+  `cpu.write()`'s bus cycle); `DebugCapabilities.write` says so and the adapter turns on
   `supportsWriteMemoryRequest` only when it can. After a write the adapter
   sends `invalidated` (variables); after every stop it sends a `memory`
   event for the whole space so the Hex Editor reads again.

extension/test/emuworker.test.ts

@@ -295,6 +295,31 @@ describe('extension emuworker', function () {
       await debug('setBreakpoints', []);
     });
 
+    it('browses the NES machine state and symbols', async function () {
+      var dir = path.join(ROOT, 'presets/nes');
+      var read = async (rel: string) => {
+        var p = path.join(dir, rel);
+        return fs.existsSync(p) ? new Uint8Array(fs.readFileSync(p)) : null;
+      };
+      var nes = await new Builder(ROOT).build({
+        platform: 'nes', mainPath: 'scroll.c', mainText: fs.readFileSync(path.join(dir, 'scroll.c'), 'utf-8'),
+        files: new ProjectFileProvider(read, ROOT, 'nes'),
+      });
+      await rpc.call('start', 'nes', nes.output, nes.files, { paused: true });
+      await debug('setBuild', { listings: nes.listings, symbols: nes.symbolmap, mainPath: 'scroll.c', paths: nes.paths });
+      var caps = await debug('capabilities');
+      assert.equal(caps.tree, true);
+      assert.equal(caps.write, true);
+      assert.deepEqual(await debug('debugTree', []), [{ name: 'state', value: '', expandable: true }]);
+      var cpu = await debug('debugTree', ['state', 'c']);
+      assert.ok(cpu.find((e: any) => e.name === 'PC'));
+      var syms = await debug('symbols');
+      assert.ok(syms.find((s: any) => s.name === '_main'));
+      // zero page, through the machine's write
+      assert.equal(await debug('writeMemory', 0x10, [0x5a]), 1);
+      assert.deepEqual(await debug('readMemory', 0x10, 1), [0x5a]);
+    });
+
     it('drives the debug adapter through the worker, as the extension does', async function () {
       var backend = new WorkerDebugBackend((method, ...args) => rpc.call('debug', method, ...args), async () => {
         await rpc.call('start', 'mw8080bw', built.output, built.files, { paused: true });

src/common/emucore.ts

@@ -305,7 +305,7 @@ export class EmuCore {
     throw new Error(`platform '${this.id}' cannot read memory`);
   }
 
-  get supportsWrite(): boolean { return !!this.machine; }
+  get supportsWrite(): boolean { return typeof this.machine?.write === 'function'; }
 
   /**
    * Write a byte through the machine's bus, as the CPU would (so an I/O

src/platform/nes.ts

@@ -107,6 +107,11 @@ class JSNESMachine {
   loadState(s) { this.p.loadState(s); }
   read(a: number) { return this.p.readAddress(a); }
   readConst(a: number) { return this.p.readAddress(a); }
+  // for the debugger: RAM, or the mapper, without cpu.write()'s bus cycle
+  write(a: number, v: number) {
+    if (a < 0x2000) this.p.nes.cpu.mem[a & 0x7ff] = v;
+    else this.p.nes.mmap.write(a, v);
+  }
   connectProbe(probe: ProbeAll) { this.p.connectProbe(probe); }
 }