Chapter 4 eMMC Command

第四章 eMMC 指令

We are going to talk about the eMMC command today.

今天我们来聊聊eMMC的指令。

In the eMMC specification, we total have 13 kinds of class command, from class 0 to class 12, among which we do not need care about class 1 Obsoleted and class 12 Reserved, class 8 Application-specific and Class 9 I/O mode are also seldom used. Then we have the 9 classes of command left. We will separate them into several sub sessions.

在eMMC规范中，我们一共有13中种类的指令，从种类0到种类12，在这些里面我们不需要关注种类1过时的指令以及种类12保留指令，还有种类8专属应用指令和种类9 I/O模式很少用到。所以我们还剩下9个种类的指令。我们将会把这些指令分成几个子话题来聊。

Before we start on the illustration for each command function, we will first use the car to demonstrate these commands' function.

在我们开始阐述这些指令的功能之前，我们先用汽车来示例这些指令的功能。

When we look at the car, we might wonder whether the space is large and comfortable (eMMC density)? whether the speed is fast (eMMC speed)? Whether the driving is convenient (easy accessing eMMC control panel) and safe (eMMC security)? Then let’s go!

当我们看一辆车的时候，我们会想空间大不大，是否舒适（eMMC容量）？速度快不快（eMMC速度）？驾驶是否方便（容易访问eMMC控制面板）以及安全（eMMC安全）？那么我们就开始吧。

Class 0 is called Basic command, it is like the basic automobile basic function, including the automobile engine from CMD0 to CMD 10, automobile brake CMD12，Gear shift CMD6，dashboard CMD13.

种类0被称为基本指令，就像汽车的基本功能，包括汽车引擎CMD0到CMD10，汽车刹车CMD12，汽车换挡CMD6，仪表盘CMD13。

Class 2 Block Read and Class 4 Block write are like automobile 4 wheels.

指令集2和指令集4块读写指令就像汽车的4个轮子一样。

Class 5 Erase command is like automobile maintenance. BKOPS (BacK ground OPerationS) is like some sort of engine oil we use for this maintenance.

指令集5擦除指令就像汽车保养。BKOPS（后台操作）就像是一种汽车的保养机油。

Class 6 Block protection and Class 10 Security Protocols (seldom used) are like automobile safety belts and air bags (seldom used too). Class 7 Lock Device command is like door locker, especially for door lock of the child seat positioned behind the driver's seat. We could never imagine how curious a kid would be.

种类6块保护和种类10安全协议（极少用到）就像是汽车的安全带和安全气囊（也极少用到）。种类7器件锁指令就像是门锁，特别是驾驶座后面的儿童座位的门锁。我们永远也想象不出小孩子的好奇心有多强烈。

Class 11 Command Queue is like some sort of light turbo engine, it will accelerate the read and write especially for random operation. We say it light turbo here is because there also is strong turbo mechanism, called WB（Write Booster） defined in the UFS latest 3.1 specification, but this is not defined in the eMMC specification.

种类11指令队列就像是一种轻量级的涡轮增压引擎，可以加速读写特别是对于随机操作。我们说它是轻量级的加速是因为有一种强涡轮增压机制，在UFS最新的3.1的规范里面称为WB（写加速），但是eMMC的规范里面没有。