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mcp-ppsspp

by dmang-dev
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TypeScript
Hybrid

ppsspp_get_registers

Read all MIPS Allegrex CPU registers (GPR, FPU, special) with no side effects. Use to inspect function arguments, return values, PC, and stack pointer for PSP reverse engineering and debugging.

Instructions

PURPOSE: Read all MIPS Allegrex CPU registers (general-purpose + FPU + special). USAGE: For reverse engineering and debugging — inspect function arguments, return values, PC, stack pointer. PSP's calling convention puts args in $a0-$a3, return in $v0, stack in $sp, return address in $ra. BEHAVIOR: No side effects — pure read. Most informative when called while emulation is paused (ppsspp_pause first); on a running CPU the snapshot is from whenever PPSSPP samples it. RETURNS: Multi-line text with all register names + hex values, grouped by class (GPR, FPU, special).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Implementation Reference

  • src/tools.ts:567-591 (handler)
    Handler that calls PPSSPP's cpu.getAllRegs via WebSocket, iterates over returned categories (GPR, FPU, special), and formats register names + hex values into multi-line text output.
    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)");
}
  • src/tools.ts:339-347 (schema)
    Tool definition/schema for ppsspp_get_registers: declares name, description, and empty inputSchema (no parameters required).
    {
  name: "ppsspp_get_registers",
  description:
    "PURPOSE: Read all MIPS Allegrex CPU registers (general-purpose + FPU + special). " +
    "USAGE: For reverse engineering and debugging — inspect function arguments, return values, PC, stack pointer. PSP's calling convention puts args in $a0-$a3, return in $v0, stack in $sp, return address in $ra. " +
    "BEHAVIOR: No side effects — pure read. Most informative when called while emulation is paused (ppsspp_pause first); on a running CPU the snapshot is from whenever PPSSPP samples it. " +
    "RETURNS: Multi-line text with all register names + hex values, grouped by class (GPR, FPU, special).",
  inputSchema: { type: "object", properties: {} },
},
  • src/tools.ts:405-613 (registration)
    Registration function that sets up MCP request handlers for ListTools (returns TOOLS array) and CallTool (switch on tool name, routing to the case for ppsspp_get_registers).
    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: ${name}`);
    }
  });
}
  • src/tools.ts:401-403 (helper)
    Helper used by the handler to format register values as 8-digit uppercase hex addresses.
    function addrHex(n: number): string {
  return `0x${n.toString(16).toUpperCase().padStart(8, "0")}`;
}

Tool Definition Quality

A4.6/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Description discloses no side effects (pure read), and clarifies timing: most informative when emulation is paused, snapshot timing on running CPU. With no annotations, the description fully carries the behavioral transparency burden.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Description is structured with clear sections (PURPOSE, USAGE, BEHAVIOR, RETURNS). Every sentence adds value and there is no redundancy. Highly efficient.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given no parameters and no output schema, the description covers purpose, usage, behavior, and return format. Could include an example output snippet, but overall complete for a read-all-registers tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Input schema has zero parameters with 100% coverage. Baseline is 4 per guidelines. Description adds no param info because none are needed.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Description clearly states it reads all MIPS Allegrex CPU registers (GPR, FPU, special). The verb 'Read' and resource 'all registers' are specific. Sibling tools include individual reads/writes, so this tool is clearly distinct as a bulk register dump.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Description provides explicit usage context: reverse engineering and debugging, inspecting function arguments, return values, PC, stack pointer. Includes PSP calling convention details. Does not explicitly list when not to use, but context is sufficient for correct selection.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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