feat(saolei): 新增纯 C 扫雷（MMIO 显示 + 中断读鼠标），扩展 CPU 外设并清理仓库

## 背景

在原有五级流水 CPU 的基础上，用一颗 RISC-V 工具链把"纯 C 写的扫雷"编译成机器码
固化进片内 ROM 运行，并为此把 MMIO 外设从"只有一个 LED 寄存器"扩展成
显示（VGA 显存）+ 七段数码管 + 鼠标事件（含中断）的完整子系统。
原 LED MMIO 的语义保持不变，原有跑马灯/中断/指令回归不受影响。

## 硬件（pipelined-cpu/srcs）

- cpu21_mmio.v：扩展成 MMIO 中枢，新增
  * 七段数码管寄存器（0x1004，8 位十六进制）
  * 鼠标寄存器组（0x1100+）：STATUS/DATA/ACK/CTRL/INPUT/TIME/FRAME/EVCNT/LEVEL/MAGIC
    —— 含 16 项事件 FIFO 与 mouse_irq_o（读空自动回 0，不丢事件）
  * 显示控制器（0x1140+）：CTRL（光标可见/背景色）、CURSOR（列、行）
  * 显存窗口（0x2000-0x27FF）：写端口输出到板级顶层的双口 RAM，读保持组合读
  * LEVEL（0x1120）：软件中断寄存器，写 1 拉起 level_irq_o（用作"关卡入口"）
  * 地址译码、字节写合并、读数据 mux 全部按原风格实现
- 新增外设 RTL：cpu21_vga.v（640x480@60 按格子扫描，8x8 字模放大 2 倍）、
  cpu21_seg7.v（8 位数码管动态扫描）、cpu21_pointer.v（5 向按键→鼠标事件，1 ms 去抖
  + 事件排队）、cpu21_ps2_mouse.v（可选真鼠标，PS/2 11 位帧接收 + 3 字节包解析）
- cpu21_riscv_redirect_int_bpb.v：新增外设总线端口（显存写/读回、鼠标事件输入、
  中断输出、数码管数据、帧脉冲），例化扩展后的 cpu21_mmio
- cpu21_board_top.v：接入显存双口 RAM + VGA + 数码管 + 鼠标事件源，中断接线为
  irq_i = {SW2, LEVEL|SW1, 鼠标|SW0}；ROM 宏切换（定义 SAOLEI_ROM 加载扫雷程序）；
  ROM_WORDS 1024→8192
- cpu21_board_top.xdc：新增按键、SW[3]、8 位数码管、VGA、PS/2 的全部引脚约束
- tb_board_top.v：新端口显式接 0/1，避免悬空影响原跑马灯回归
- create_project.tcl：把 cpu21_saolei_rom.vh 按 Verilog Header 条件加入

## 软件（saolei/）

- sw/mmio.h：全部 MMIO 地址与格子编码（换地址只改这一个文件）
- sw/saolei.c：纯 C 扫雷 —— 背景"伪操作系统" main()（开始界面）+ 关卡 level_main()
  （在 IRQ1 里跑完整局）+ 棋盘位图/布雷（首点安全）/BFS 展开/插旗/胜负判定/逐格绘制
- sw/isr.c：**中断读鼠标的代码**。三个固定地址入口：
  * isr1_entry（.text.isr1=0x100）关卡入口：保存全部调用者保存寄存器 +
    csrrsi 打开 MIE（让鼠标中断可嵌套）→ level_main
  * isr2_entry（.text.isr2=0x200）鼠标读取：只存 ra → 纯 C 主体 isr_body
  * isr3_entry（.text.isr3=0x300）备用：直接 uret
- sw/start.c：设 sp、清 .bss、进 main（只有这一处必要内联汇编）
- sw/linker.ld：复位 0x0、三个中断入口 0x100/0x200/0x300、栈顶 0x0FFC；
  用 ASSERT 禁止 .data/.rodata（这颗核读不到 ROM 里的数据）

## 构建与工具链适配（saolei/tools）

- build.ps1：一键 C → .o → ELF → .hex + cpu21_saolei_rom.vh，任一步失败立刻停止
- check_isa.py：用"指令白名单"逐条检查反汇编，出现本核未实现的指令即报错并给修复提示
- elf2hex.py：裸二进制 → $readmemh hex + ROM 初始化头文件
- 三处针对本核的关键配置（都已写进脚本注释）：
  1) -march=rv32im_zicsr（GCC 15 起 rv32im 不含 Zicsr，csrrsi 会报错）
  2) 不能禁链接器松弛：gcc 函数调用默认是 auipc+jalr，靠松弛压成 jal，
     禁掉后 35 条 auipc 会留在代码里（本核没有 auipc）；
     用 -msmall-data-limit=0 防止松弛引入 gp 相对寻址
  3) 中断入口地址必须写在段声明上（.text.isr1 0x100 : ...），
     只写 ". = 0x100;" 会被 ld 忽略（实测 isr1 掉到了 0x14）
- 实测结果：text=3368B、data=0、bss=1436B，842 条指令全部通过 ISA 检查，
  入口地址 _start=0x0 / isr1_entry=0x100 / isr2_entry=0x200 / isr3_entry=0x300

## 仓库清理

- 删除被工程取代的 saolei/hw、saolei/constrs（外设已并入 srcs/rtl）
- 删除全部 Vivado 生成物：.xpr、.runs、.sim、.cache、.hw、.ip_user_files、.Xil、
  vivado.jou/log —— 需要工程时用 source create_project.tcl 一键重建（约 0.3 MB 源文件）
- .gitignore 增加 saolei/build/（构建产物可一键重建）

## 文档

- README：更新目录结构、仓库约定（不放生成物）、MMIO 地址表、文件与模块划分表、
  上板说明，新增"扫雷程序（saolei/）"章节
- saolei/README.md：重写 —— 程序结构（背景/关卡/鼠标 + 三个中断入口）、
  本核指令子集与对应写法、构建步骤与实测数据、MMIO 地址表、上板/仿真步骤、
  操作说明、验证状态与已知可改进项

## 验证状态（如实说明）

- 已实测：C 工具链链路（编译/链接/ISA 检查/hex 生成/入口地址逐条核对）
- 未验证：所有 RTL 未经综合与仿真（本机无 Vivado），C 程序也未在仿真器/硬件上运行过；
  建议先跑 tools/run_regress.ps1 确认原回归仍全 PASS，再用 SAOLEI_ROM 宏做行为仿真

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pipelined-cpu/srcs/rom/mmio_test.hex

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