Seven hardware diagrams, drawn in relief七种硬件框图，用凹凸画出来

A · State machineA · 状态机

States are raised blocks, transitions are embossed lines, and each condition sits in a sunken pill. Sunken means condition, raised means state — the reader never needs a legend. The entry state carries the accent colour. Below are the kernel's four runtime-PM states.状态用凸起的块，迁移用浮雕线，条件写在凹进去的药丸里——凹的是条件，凸的是状态，不用看图例也分得清谁是谁。入口状态给强调色。下面画的是内核 runtime PM 的四个状态。

B · Timing diagramB · 时序图

The waveforms live inside a sunken panel — it is a screen, so sunken is the honest shape. Traces are embossed strokes floating on it; alignment guides and measurement bars sit one layer below in the surface colour, so they never compete with the traces. Below is a panel power-on sequence.波形放进一块凹陷的面板里——它本来就是一块显示屏，凹进去比凸出来对。信号线用浮雕描边浮在面板上；基准虚线和量取条用面料色，压在波形下面一层，不抢。下面是一块屏的上电时序。

C · Register bitfieldC · 寄存器位域

Reserved bits are sunken dead zones, usable bits are raised — you know which bits you may touch without reading the access column. The write-only self-clearing bit takes the accent colour, because it is the one people get wrong: it always reads back 0, and that does not mean the write missed.保留位画成凹进去的死区，能用的位凸起——不用读属性列就知道哪些位是能碰的。只写自清的位给强调色，因为它是最容易写错的一类（读回来永远是 0，不代表没生效）。

D · IP block diagramD · IP 内部框图

Groups sit in sunken wells, modules are raised blocks inside them — a well says these belong together, a block says this is one thing. The bus is a sunken rail: masters attach above it, slaves below. That is the reading convention; break it and every reader has to trace each line to find who initiates a transfer.分组用凹陷的槽装，模块用凸起的块摆进去——槽是「这几个归一起」，块是「这是一个东西」。总线画成一条凹槽轨：主设备接在轨上方，从设备接在下方，这是读图的约定，不按这个摆，看图的人得逐条线追才知道谁发起访问。

E · Memory mapE · 内存布局

The address space runs top to bottom and anything you cannot reach is drawn as a groove — reserved regions, holes, the secure world. The right-hand column says what each region is for, because that is what a reader of this diagram actually asks. Not how big it is.地址空间从上往下排，访问不到的区间画成凹槽——保留区、空洞、安全世界，凹下去的一眼就是「这块你碰不了」。右边留一列写用途，因为读这种图的人真正要问的是「这块归谁」，不是「它多大」。

F · Data pathF · 数据通路

Stages run left to right and under each one is what it turned the data into — a data path drawn as a row of boxes leaves the reader still not knowing what happened in between. Places that store data use the deep block; places that transform it use the plain raised block.一级一级往右走，每级底下写它把数据变成了什么——数据通路图最容易画成「几个盒子连起来」，那样看完还是不知道中间发生了什么。存数据的地方用深色块，加工数据的地方用普通凸块，两类分开。

G · Clock treeG · 时钟树

The mux and the gate in a clock tree already are controls — picking one of the divided outputs is a segmented control, enabling the branch is a switch. Draw them as the controls they are and the reader learns no new symbols, while which path is live reads at a glance.时钟树里的选择器和门控本来就是控件——分频后选哪一路是个分段控件，开不开这条时钟是个开关。直接拿控件画，不另造图形：看图的人不用学新符号，而且哪一路是通的一眼看得出。

H · Cache line statesH · 缓存一致性状态

Four states, and the one that costs you is S — the accent marks it because writing to a shared line is the transition that has to stop every other core first. The dashed edge is that write. A driver that memcpy()s into a buffer another master is reading lives on that dashed line.四个状态，代价最大的是 S —— 给它强调色，是因为往一行共享数据里写，这次跳转必须先把别的核全叫停。那条虚线就是这次写。一个驱动往别的主设备正在读的缓冲区里 memcpy，走的就是这条虚线。

I · DMA descriptor chainI · DMA 描述符链

Each descriptor is a raised block and its next pointer is the groove between them. The last one has no next, so that slot is drawn as a dead groove rather than a value — the chain ending and a value being present then look different, which matters because a descriptor left pointing at freed memory is the bug this figure is about.每块描述符是凸的，它的 next 指针就是块之间那道凹槽。最后一块没有 next，所以那一格画成凹陷的死区而不是一个值 —— 这样「链在这里结束」和「这里有个值」长得不一样，而这很要紧，因为描述符指向已经释放的内存正是这张图要讲的那个 bug。

J · Bus transaction timingJ · 总线事务时序

Protocol level, not electrical level — the question a driver author brings here is which beat stopped getting acknowledged. The two measure bars name the two failures that look identical from userspace: no ACK on the address means nobody answered, no ACK on the register means the chip is there but does not know that register.这是协议层不是电气层 —— 写驱动的人来看这张图，问的是从哪一拍开始没人应答。底下两条量取条标出的，正是从用户态看长得一模一样的两种失败：地址没 ACK 是根本没人答，寄存器没 ACK 是器件在、但不认这个寄存器。

Terms used above上面用到的术语

A diagram that needs a word the reader does not have is not a diagram, it is a quiz. Every term below appears somewhere on this page.一张图要是用了读者没有的词，那不是图，是考试。下面每个词在这页上都出现过。