retroarch_write_memory

Instructions

Implementation Reference

• src/tools.ts:211-214 (handler)

  Handler for the retroarch_write_memory tool. Calls ra.writeMemory() with the address and bytes from the request args, then returns a success message with the number of bytes written.

  case "retroarch_write_memory": {
    const n = await ra.writeMemory(p.address as number, p.bytes as number[]);
    return ok(`Wrote ${n} bytes → ${addrHex(p.address as number)}`);
  }

• src/tools.ts:55-71 (schema)

  Schema/registration definition for retroarch_write_memory. Defines name, description (with MEMORY_NOTE about core memory map), and inputSchema requiring 'address' (integer) and 'bytes' (array of integers 0-255, 1-4096 items).

  {
    name: "retroarch_write_memory",
    description: `Write a byte sequence to emulated memory via the system memory map. Returns the number of bytes actually written (may be less than requested if a read-only descriptor is hit). Disables hardcore mode for the session.\n\n${MEMORY_NOTE}`,
    inputSchema: {
      type: "object",
      required: ["address", "bytes"],
      properties: {
        address: { type: "integer", description: "Memory address" },
        bytes: {
          type: "array",
          items: { type: "integer", minimum: 0, maximum: 255 },
          minItems: 1,
          maxItems: 4096,
        },
      },
    },
  },

• src/retroarch.ts:166-179 (helper)

  The RetroArchClient.writeMemory() method that performs the actual WRITE_CORE_MEMORY UDP command. Converts bytes to hex string, sends to RetroArch via UDP, and parses the response to return the count of bytes written.

  /** Memory write via libretro's system memory map (preferred). */
  async writeMemory(addr: number, bytes: Uint8Array | number[]): Promise<number> {
    if (bytes.length === 0)    throw new Error("at least one byte required");
    if (bytes.length > 4096)   throw new Error("byte count exceeds 4096 limit");
    const hex = Array.from(bytes).map((b) => b.toString(16).padStart(2, "0")).join(" ");
    const cmd = `WRITE_CORE_MEMORY 0x${addr.toString(16)} ${hex}`;
    const r = (await this.query(cmd)).toString().trim();
    // "WRITE_CORE_MEMORY <addr> <bytes_written>" or "<addr> -1 <error>"
    const m = r.match(/^WRITE_CORE_MEMORY\s+\S+\s+(-?\d+)(?:\s+(.+))?$/);
    if (!m) throw new Error(`unexpected WRITE_CORE_MEMORY reply: ${r}`);
    const n = parseInt(m[1], 10);
    if (n < 0) throw new Error(`WRITE_CORE_MEMORY failed: ${m[2] ?? "(no error message)"}`);
    return n;
  }

• src/tools.ts:176-246 (registration)

  The registerTools function that registers all tools including retroarch_write_memory via the MCP CallToolRequestSchema handler.

  export function registerTools(server: Server, ra: RetroArchClient): 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>;
  
      switch (name) {
        case "retroarch_ping": {
          const v = await ra.getVersion();
          return ok(`OK — RetroArch ${v}`);
        }
  
        case "retroarch_get_status": {
          const s = await ra.getStatus();
          if (s.state === "contentless") return ok("No content loaded");
          return ok(
            `State:  ${s.state}\n` +
            `System: ${s.system}\n` +
            `Game:   ${s.game}\n` +
            `CRC32:  ${s.crc32 ?? "(none reported)"}`,
          );
        }
  
        case "retroarch_get_config": {
          const v = await ra.getConfigParam(p.name as string);
          return ok(`${p.name} = ${v}`);
        }
  
        case "retroarch_read_memory": {
          const bytes = await ra.readMemory(p.address as number, p.length as number);
          const hex = Array.from(bytes).map((b) => b.toString(16).padStart(2, "0").toUpperCase()).join(" ");
          return ok(`${addrHex(p.address as number)} [${bytes.length} bytes]:\n${hex}`);
        }
  
        case "retroarch_write_memory": {
          const n = await ra.writeMemory(p.address as number, p.bytes as number[]);
          return ok(`Wrote ${n} bytes → ${addrHex(p.address as number)}`);
        }
  
        case "retroarch_read_ram": {
          const bytes = await ra.readRam(p.address as number, p.length as number);
          const hex = Array.from(bytes).map((b) => b.toString(16).padStart(2, "0").toUpperCase()).join(" ");
          return ok(`${addrHex(p.address as number)} [${bytes.length} bytes, CHEEVOS]:\n${hex}`);
        }
  
        case "retroarch_write_ram": {
          await ra.writeRam(p.address as number, p.bytes as number[]);
          return ok(`Wrote ${(p.bytes as number[]).length} bytes → ${addrHex(p.address as number)} (CHEEVOS, no ack)`);
        }
  
        case "retroarch_pause_toggle":  await ra.pauseToggle();   return ok("Pause toggled");
        case "retroarch_frame_advance": await ra.frameAdvance();  return ok("Advanced one frame");
        case "retroarch_reset":         await ra.reset();         return ok("Game reset");
        case "retroarch_screenshot":    await ra.screenshot();    return ok("Screenshot saved to RetroArch's configured screenshot directory");
        case "retroarch_show_message": {
          await ra.showMessage(p.message as string);
          return ok(`Showed: ${p.message}`);
        }
  
        case "retroarch_save_state_current":  await ra.saveStateCurrent();          return ok("Saved to current slot");
        case "retroarch_load_state_current":  await ra.loadStateCurrent();          return ok("Loaded from current slot");
        case "retroarch_load_state_slot":     await ra.loadStateSlot(p.slot as number); return ok(`Loaded from slot ${p.slot}`);
        case "retroarch_state_slot_plus":     await ra.stateSlotPlus();             return ok("Incremented current slot");
        case "retroarch_state_slot_minus":    await ra.stateSlotMinus();            return ok("Decremented current slot");
  
        default:
          throw new Error(`Unknown tool: ${name}`);
      }
    });
  }