ppsspp_read_string

Instructions

Implementation Reference

• src/tools.ts:452-455 (handler)

  Handler for ppsspp_read_string tool. Calls PPSSPP's 'memory.readString' with the address and 'utf-8' type, then returns the string in JSON format: 'ADDR_HEX: "STRING"'.

  case "ppsspp_read_string": {
    const r = await pp.call<{ value: string }>("memory.readString", { address: a(), type: "utf-8" });
    return ok(`${addrHex(a())}: ${JSON.stringify(r.value ?? "")}`);
  }

• src/tools.ts:127-142 (schema)

  Tool schema definition for ppsspp_read_string. Defines the tool name, description (null-terminated UTF-8 string reader), and input schema requiring an 'address' integer parameter.

  {
    name: "ppsspp_read_string",
    description:
      "PURPOSE: Read a null-terminated UTF-8 string from PSP memory at the given address. " +
      "USAGE: Use for in-game text, character names, dialogue, file names — anywhere the PSP stores a C-style null-terminated string. Stops at the first 0x00 byte. " +
      "BEHAVIOR: No side effects — pure read. Reads bytes until null terminator, decodes as UTF-8. Returns an error if the address is outside valid memory, or if the string runs past valid memory before hitting a null. " +
      "RETURNS: Single line 'ADDR_HEX: \"STRING\"'.",
    inputSchema: {
      type: "object",
      required: ["address"],
      properties: {
        address: { type: "integer", minimum: 0, description: ADDRESS_PARAM_DESC },
      },
      additionalProperties: false,
    },
  },

• src/tools.ts:405-613 (registration)

  The registerTools function registers the tool list and call handler on the MCP server. The ppsspp_read_string case is part of the CallToolRequestSchema switch statement.

  export function registerTools(server: Server, pp: PpssppClient): void {
    server.setRequestHandler(ListToolsRequestSchema, async () => ({ tools: TOOLS }));
  
    server.setRequestHandler(CallToolRequestSchema, async (req) => {
      const { name, arguments: args = {} } = req.params;
      const p = args as Record<string, unknown>;
      const a = () => p.address as number;
  
      switch (name) {
        case "ppsspp_ping": {
          const r = await pp.call<{ version?: string; name?: string }>("version");
          return ok(`pong (${r.name ?? "PPSSPP"} ${r.version ?? "(unknown version)"})`);
        }
  
        case "ppsspp_get_info": {
          const status = await pp.call<{ game?: { id?: string; title?: string; version?: string } | null; paused?: boolean; stepping?: boolean }>("game.status");
          const lines: string[] = [];
          if (status.game) {
            lines.push(`Title:   ${status.game.title ?? "(unavailable)"}`);
            lines.push(`Disc ID: ${status.game.id ?? "(unavailable)"}`);
            lines.push(`Version: ${status.game.version ?? "(unavailable)"}`);
          } else {
            lines.push("No game loaded.");
          }
          const state = status.stepping ? "stepping (paused)" : status.paused ? "paused" : "running";
          lines.push(`State:   ${state}`);
          return ok(lines.join("\n"));
        }
  
        case "ppsspp_read8": {
          const r = await pp.call<{ value: number }>("memory.read_u8", { address: a() });
          return ok(`${addrHex(a())}: ${fmtHex(r.value)}`);
        }
        case "ppsspp_read16": {
          const r = await pp.call<{ value: number }>("memory.read_u16", { address: a() });
          return ok(`${addrHex(a())}: ${fmtHex(r.value)}`);
        }
        case "ppsspp_read32": {
          const r = await pp.call<{ value: number }>("memory.read_u32", { address: a() });
          return ok(`${addrHex(a())}: ${fmtHex(r.value)}`);
        }
        case "ppsspp_read_range": {
          const r = await pp.call<{ base64: string }>("memory.read", { address: a(), size: p.size });
          const bytes = Buffer.from(r.base64 ?? "", "base64");
          const hex = Array.from(bytes).map((b) => b.toString(16).padStart(2, "0").toUpperCase()).join(" ");
          return ok(`${addrHex(a())} [${bytes.length} bytes]:\n${hex}`);
        }
        case "ppsspp_read_string": {
          const r = await pp.call<{ value: string }>("memory.readString", { address: a(), type: "utf-8" });
          return ok(`${addrHex(a())}: ${JSON.stringify(r.value ?? "")}`);
        }
  
        case "ppsspp_write8": {
          await pp.call("memory.write_u8", { address: a(), value: p.value });
          return ok(`Wrote ${fmtHex(p.value)} → ${addrHex(a())}`);
        }
        case "ppsspp_write16": {
          await pp.call("memory.write_u16", { address: a(), value: p.value });
          return ok(`Wrote ${fmtHex(p.value)} → ${addrHex(a())}`);
        }
        case "ppsspp_write32": {
          await pp.call("memory.write_u32", { address: a(), value: p.value });
          return ok(`Wrote ${fmtHex(p.value)} → ${addrHex(a())}`);
        }
        case "ppsspp_write_range": {
          const bytes = Buffer.from(p.bytes as number[]);
          const base64 = bytes.toString("base64");
          await pp.call("memory.write", { address: a(), base64 });
          return ok(`Wrote ${bytes.length} bytes → ${addrHex(a())}`);
        }
  
        case "ppsspp_press_buttons": {
          await pp.call("input.buttons.send", { buttons: p.buttons });
          const pressed = Object.entries(p.buttons as Record<string, boolean>)
            .filter(([, v]) => v).map(([k]) => k);
          return ok(`Set buttons: ${pressed.length ? pressed.join("+") : "(all released)"}`);
        }
        case "ppsspp_press_button": {
          await pp.call("input.buttons.press", { button: p.button, duration: p.duration ?? 1 });
          return ok(`Pressed ${p.button} for ${p.duration ?? 1} frames (auto-released)`);
        }
        case "ppsspp_send_analog": {
          await pp.call("input.analog.send", { stick: p.stick, x: p.x, y: p.y });
          return ok(`Set analog stick ${p.stick} to (${p.x}, ${p.y})`);
        }
  
        case "ppsspp_pause": {
          // cpu.stepping is fire-and-forget per PPSSPP source ("No immediate
          // response. Once CPU is stepping, a 'cpu.stepping' event will be
          // sent."). Send it, then poll cpu.status until stepping=true.
          await pp.fireAndForget("cpu.stepping");
          await pp.waitForState((s) => s.stepping === true);
          return ok("Emulation paused");
        }
        case "ppsspp_resume": {
          await pp.fireAndForget("cpu.resume");
          await pp.waitForState((s) => s.stepping === false);
          return ok("Emulation resumed");
        }
        case "ppsspp_step": {
          const r = await pp.call<{ pc?: number }>("cpu.stepInto");
          return ok(`Stepped one instruction. PC: ${r.pc !== undefined ? addrHex(r.pc) : "(unknown)"}`);
        }
        case "ppsspp_reset": {
          await pp.call("game.reset");
          return ok("Game reset");
        }
        case "ppsspp_screenshot": {
          // PPSSPP's gpu.buffer.* events all require CORE_STEPPING_CPU (or GPU
          // stepping) state — they fail with "Neither CPU or GPU is stepping"
          // otherwise. We transparently pause→capture→resume so callers can
          // screenshot any time without managing pause state. If the emulator
          // was already paused, we leave it paused.
          //
          // source='render' (default) uses gpu.buffer.renderColor → reads the
          // active GPU render target. Safer: GPU_GetCurrentFramebuffer hits a
          // different code path than the crash-prone GPU_GetOutputFramebuffer.
          //
          // source='output' uses gpu.buffer.screenshot → reads the final
          // composited output (what's on screen, post scaling/shaders). Can
          // CRASH PPSSPP on some games: upstream has an `_assert_(buf != nullptr)`
          // after GPU_GetOutputFramebuffer that fires when the function returns
          // true with a null buffer (observed on some homebrew). We can't catch
          // a process abort from outside, but v0.1.2's auto-reconnect means MCP
          // recovers when PPSSPP is relaunched.
          const source = (p.source as string | undefined) ?? "render";
          const event  = source === "output" ? "gpu.buffer.screenshot" : "gpu.buffer.renderColor";
          const statusBefore = await pp.call<{ stepping?: boolean; paused?: boolean }>("cpu.status");
          const wasStepping = !!statusBefore.stepping;
          if (!wasStepping) {
            await pp.fireAndForget("cpu.stepping");
            await pp.waitForState((s) => s.stepping === true);
          }
          try {
            // type: "base64" returns the raw base64 payload; the default "uri"
            // returns a "data:image/png;base64,..." prefix which we'd have to strip.
            const r = await pp.call<{ base64?: string; uri?: string }>(event, { type: "base64" });
            let b64 = r.base64;
            if (!b64 && r.uri) {
              // Belt-and-suspenders: if PPSSPP returned a URI anyway, strip the prefix.
              const m = /^data:image\/png;base64,(.*)$/.exec(r.uri);
              if (m) b64 = m[1];
            }
            if (!b64) {
              throw new Error(`PPSSPP did not return screenshot data from ${event} (no game loaded, or framebuffer not readable?)`);
            }
            return {
              content: [
                { type: "text" as const, text: `Screenshot captured (source: ${source}, event: ${event}).` },
                { type: "image" as const, data: b64, mimeType: "image/png" },
              ],
            };
          } finally {
            if (!wasStepping) {
              try {
                await pp.fireAndForget("cpu.resume");
                await pp.waitForState((s) => s.stepping === false, { timeoutMs: 2000 });
              } catch { /* best-effort */ }
            }
          }
        }
  
        case "ppsspp_get_registers": {
          // PPSSPP's cpu.getAllRegs returns categories with PARALLEL arrays:
          //   { categories: [{ name, registerNames: [...], uintValues: [...], floatValues: [...] }] }
          // Not an array of {name, value} objects as I first assumed.
          const r = await pp.call<{
            categories?: Array<{
              name: string;
              registerNames?: string[];
              uintValues?: number[];
              floatValues?: string[];
            }>;
          }>("cpu.getAllRegs");
          const lines: string[] = [];
          for (const cat of r.categories ?? []) {
            lines.push(`── ${cat.name} ──`);
            const names = cat.registerNames ?? [];
            const vals  = cat.uintValues ?? [];
            for (let i = 0; i < Math.max(names.length, vals.length); i++) {
              const nm = names[i] ?? `r${i}`;
              const v  = vals[i];
              lines.push(`  ${nm.padEnd(8)} = ${v !== undefined ? addrHex(v) : "(unavailable)"}`);
            }
          }
          return ok(lines.join("\n") || "(no registers returned)");
        }
  
        case "ppsspp_breakpoint_add": {
          await pp.call("cpu.breakpoint.add", { address: a() });
          return ok(`Breakpoint added at ${addrHex(a())}`);
        }
        case "ppsspp_breakpoint_remove": {
          await pp.call("cpu.breakpoint.remove", { address: a() });
          return ok(`Breakpoint removed at ${addrHex(a())}`);
        }
        case "ppsspp_breakpoint_list": {
          const r = await pp.call<{ breakpoints?: Array<{ address: number; enabled?: boolean; condition?: string }> }>("cpu.breakpoint.list");
          const bps = r.breakpoints ?? [];
          if (bps.length === 0) return ok("No breakpoints set.");
          const lines = bps.map((b) => `  ${addrHex(b.address)} ${b.enabled === false ? "(disabled)" : ""}${b.condition ? ` if ${b.condition}` : ""}`);
          return ok(`${bps.length} breakpoint${bps.length === 1 ? "" : "s"}:\n${lines.join("\n")}`);
        }
  
        default:
          throw new Error(`Unknown tool: ${name}`);
      }
    });
  }

• src/ppsspp.ts:226-262 (helper)

  The PpssppClient.call method used by the handler to send a ticketed JSON-RPC request (event: 'memory.readString') to PPSSPP via WebSocket and await the response.

  async call<T extends Record<string, unknown> = Record<string, unknown>>(
    event: string,
    params: Record<string, unknown> = {},
  ): Promise<T> {
    // Auto-(re)connect on demand. PPSSPP can be launched, closed, relaunched
    // at any point during the MCP server's lifetime; ensureConnected() will
    // bring the socket back up (or throw a clear error if PPSSPP isn't
    // reachable). Without this, a single failed connect at MCP boot would
    // leave every subsequent tool call broken until MCP-client restart.
    await this.ensureConnected();
    return new Promise<T>((resolve, reject) => {
      const ticket = `t${this.nextTicket++}`;
      const pending: PendingCmd = {
        ticket,
        resolve: (r) => resolve(r as T),
        reject,
      };
  
      const timer = setTimeout(() => {
        this.inflight.delete(ticket);
        reject(new Error(
          `PPSSPP call "${event}" timed out (${this.timeoutMs}ms) — ` +
          `is PPSSPP running with "Allow remote debugger" enabled?`,
        ));
      }, this.timeoutMs);
      const origResolve = pending.resolve, origReject = pending.reject;
      pending.resolve = (r) => { clearTimeout(timer); origResolve(r); };
      pending.reject  = (e) => { clearTimeout(timer); origReject(e); };
  
      this.inflight.set(ticket, pending);
      const msg = JSON.stringify({ event, ticket, ...params });
      if (process.env.MCP_PPSSPP_DEBUG) {
        process.stderr.write(`[trace] TX: ${msg}\n`);
      }
      this.ws!.send(msg);
    });
  }