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<ol class="chapter"><li class="chapter-item expanded "><a href="../intro/index.html"><strong aria-hidden="true">1.</strong> 简介</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../intro/hardware.html"><strong aria-hidden="true">1.1.</strong> 硬件</a></li><li class="chapter-item expanded "><a href="../intro/no-std.html"><strong aria-hidden="true">1.2.</strong> no_std</a></li><li class="chapter-item expanded "><a href="../intro/tooling.html"><strong aria-hidden="true">1.3.</strong> 工具</a></li><li class="chapter-item expanded "><a href="../intro/install.html"><strong aria-hidden="true">1.4.</strong> 安装</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../intro/install/linux.html"><strong aria-hidden="true">1.4.1.</strong> Linux</a></li><li class="chapter-item expanded "><a href="../intro/install/macos.html"><strong aria-hidden="true">1.4.2.</strong> MacOS</a></li><li class="chapter-item expanded "><a href="../intro/install/windows.html"><strong aria-hidden="true">1.4.3.</strong> Windows</a></li><li class="chapter-item expanded "><a href="../intro/install/verify.html"><strong aria-hidden="true">1.4.4.</strong> 验证安装</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="../start/index.html"><strong aria-hidden="true">2.</strong> 入门</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../start/qemu.html"><strong aria-hidden="true">2.1.</strong> QEMU</a></li><li class="chapter-item expanded "><a href="../start/hardware.html"><strong aria-hidden="true">2.2.</strong> 硬件</a></li><li class="chapter-item expanded "><a href="../start/registers.html"><strong aria-hidden="true">2.3.</strong> 内存映射寄存器</a></li><li class="chapter-item expanded "><a href="../start/semihosting.html"><strong aria-hidden="true">2.4.</strong> 半主机</a></li><li class="chapter-item expanded "><a href="../start/panicking.html"><strong aria-hidden="true">2.5.</strong> 恐慌</a></li><li class="chapter-item expanded "><a href="../start/exceptions.html"><strong aria-hidden="true">2.6.</strong> 异常</a></li><li class="chapter-item expanded "><a href="../start/interrupts.html"><strong aria-hidden="true">2.7.</strong> 中断</a></li><li class="chapter-item expanded "><a href="../start/io.html"><strong aria-hidden="true">2.8.</strong> IO</a></li></ol></li><li class="chapter-item expanded "><a href="../peripherals/index.html" class="active"><strong aria-hidden="true">3.</strong> 外设</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../peripherals/a-first-attempt.html"><strong aria-hidden="true">3.1.</strong> 初试Rust</a></li><li class="chapter-item expanded "><a href="../peripherals/borrowck.html"><strong aria-hidden="true">3.2.</strong> 借用检查器</a></li><li class="chapter-item expanded "><a href="../peripherals/singletons.html"><strong aria-hidden="true">3.3.</strong> 单例</a></li></ol></li><li class="chapter-item expanded "><a href="../static-guarantees/index.html"><strong aria-hidden="true">4.</strong> 静态保证</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../static-guarantees/typestate-programming.html"><strong aria-hidden="true">4.1.</strong> 类型状态机编程</a></li><li class="chapter-item expanded "><a href="../static-guarantees/state-machines.html"><strong aria-hidden="true">4.2.</strong> 外设作为状态机</a></li><li class="chapter-item expanded "><a href="../static-guarantees/design-contracts.html"><strong aria-hidden="true">4.3.</strong> 设计合约</a></li><li class="chapter-item expanded "><a href="../static-guarantees/zero-cost-abstractions.html"><strong aria-hidden="true">4.4.</strong> 零成本抽象</a></li></ol></li><li class="chapter-item expanded "><a href="../portability/index.html"><strong aria-hidden="true">5.</strong> 可移植性</a></li><li class="chapter-item expanded "><a href="../concurrency/index.html"><strong aria-hidden="true">6.</strong> 并发</a></li><li class="chapter-item expanded "><a href="../collections/index.html"><strong aria-hidden="true">7.</strong> 容器</a></li><li class="chapter-item expanded "><a href="../c-tips/index.html"><strong aria-hidden="true">8.</strong> 嵌入式C开发人员的技巧</a></li><li class="chapter-item expanded "><a href="../interoperability/index.html"><strong aria-hidden="true">9.</strong> 互操作性</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../interoperability/c-with-rust.html"><strong aria-hidden="true">9.1.</strong> Rust中使用C代码</a></li><li class="chapter-item expanded "><a href="../interoperability/rust-with-c.html"><strong aria-hidden="true">9.2.</strong> C中使用Rust代码</a></li></ol></li><li class="chapter-item expanded "><a href="../unsorted/index.html"><strong aria-hidden="true">10.</strong> 其他主题</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../unsorted/speed-vs-size.html"><strong aria-hidden="true">10.1.</strong> 优化：速度大小的权衡</a></li><li class="spacer"></li></ol></li><li class="chapter-item expanded "><a href="../appendix/glossary.html">Appendix A: Glossary</a></li></ol>
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<h1><a class="header" href="#外设" id="外设">外设</a></h1>
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<h2><a class="header" href="#什么是外围设备" id="什么是外围设备">什么是外围设备？</a></h2>
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<p>大多数微控制器都是SoC,不仅仅具有CPU，RAM或闪存，芯片内部还集成了各种设备,用于与外部系统进行交互. 比如通过传感器，电机控制器直接或间接与周围环境进行交互。 或其他的人机界面，例如显示器或键盘。这些组件统称为外围设备。</p>
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<p>这些外围设备很有用，因为它们使开发人员可以将一部分工作分派出去，而不必全部由软件来实现。与台式机开发人员将图形处理任务分派给显卡的方式类似，嵌入式开发人员可以将某些任务分派到外围设备，从而使CPU可以将时间花在更重要的事情上，或者不做任何事以节省功耗。</p>
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<p>如果您看一下1970年代或1980年代的老式家用计算机中的主板(实际上，以前的台式机与今天的嵌入式系统相去不远)，您会看到：</p>
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<ul>
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<li>处理器</li>
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<li>RAM芯片</li>
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<li>ROM芯片</li>
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<li>I/O控制器</li>
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</ul>
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<p>RAM芯片，ROM芯片和I/O控制器(此系统中的外围设备)通过“总线”连接到处理器。处理器通过地址总线选择与哪个设备进行通信，通过数据总线传输数据。在我们的嵌入式微控制器中，原理都是一样的--只是将所有内容包装在一块芯片内。</p>
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<p>但是与显卡不同的是,显卡一般提供了像Vulkan，Metal或OpenGL之类的软件API，而嵌入式外设通过内存映射的方式,直接将硬件接口暴露给我们的微控制器。</p>
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<h2><a class="header" href="#线性和物理内存地址空间" id="线性和物理内存地址空间">线性和物理内存地址空间</a></h2>
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<p>在微控制器上，将一些数据写入任意地址，例如<code>0x4000_0000</code>或<code>0x0000_0000</code>，也可能是完全有效的操作。</p>
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<p>与嵌入式系统不同,在台式机系统上，对内存的访问由内存管理单元(MMU)严格控制,MMU有两个主要职责：强制执行对内存的访问权限(防止一个进程读取或修改另一进程的内存)；并将物理内存的地址重新映射到软件中使用的虚拟内存地址。微控制器通常没有MMU，而仅使用实际物理地址。</p>
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<p>尽管32位微控制器具有从0x0000_0000到0xFFFF_FFFF的物理和线性地址空间，但它们通常仅使用该范围的几百K字节作为实际内存。这留下了大量的可用地址空间。在前面的章节中，我们讨论了位于地址“0x2000_0000”上的RAM。如果我们的RAM大小为64 KiB(即最大地址为0xFFFF)，则地址“0x2000_0000”到“0x2000_FFFF”将对应于我们的RAM。当我们写入位于地址“0x2000_1234”的变量时， 某些逻辑检测地址的上半部分(在此示例中为0x2000)，然后激活RAM控制器，由RAM控制器来处理地址的下半部分(在这种情况下为0x1234)。在Cortex-M上，我们将Flash ROM映射到地址“0x0000_0000”到地址“0x0007_FFFF”之间(如果我们有512 KiB Flash ROM)。微控制器设计人员没有忽略这两个区域之间的剩余地址空间，而是将某些内存位置映射给了外设。最终看起来像这样：</p>
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<p><img src="../assets/nrf52-memory-map.png" alt="" /></p>
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<p><a href="http://infocenter.nordicsemi.com/pdf/nRF52832_PS_v1.1.pdf">Nordic nRF52832手册(pdf)</a></p>
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<h2><a class="header" href="#内存映射的外围设备" id="内存映射的外围设备">内存映射的外围设备</a></h2>
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<p>乍看之下，与这些外设的交互非常简单--将正确的数据写入正确的地址。例如，通过串行端口发送32位数据可能与将32位数据写入某个内存地址一样直接。写入后，串口外设将接管并自动发送数据。</p>
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<p>这些外设的配置工作与内存操作类似。无需调用函数来进行配置一个外设，而是公开了一块用作配置硬件的内存区域。比如将“0x8000_0000”写入SPI频率配置寄存器，SPI端口将以每秒8兆位的速度发送数据。将“0x0200_0000”写入相同的地址，SPI端口将以每秒125 Kilobits的速度发送数据。这些配置寄存器看起来像这样：</p>
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<p><img src="../assets/nrf52-spi-frequency-register.png" alt="" /></p>
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<p><a href="http://infocenter.nordicsemi.com/pdf/nRF52832_PS_v1.1.pdf">Nordic nRF52832手册(pdf)</a></p>
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<p>无论使用哪种语言，无论该语言是Assembly，C还是Rust，都是这样与硬件进行交互。</p>
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