1 eMMC 简介

eMMC 是 embedded MultiMediaCard 的简称。 eMMC 是对 MMC 的一个拓展，以满足更高标准的性能、成本、体积、稳定、易用等的需求。主要针对手机、数码相机、平板电脑等产品。eMMC主要是为了简化手机内存储器的设计，节省电路板的面积。eMMC是将NAND Flash、控制器和MMC标准接口封装到一块芯片上。
主机与设备之间的所有通信都由主机（master）控制。主机会发送一个命令，从而导致设备响应。为eMMC系统（主机和设备）定义了五种操作模式：

•  Boot mode:
  The device will be in boot mode after power cycle, reception of CMD0 with argument of 0xF0F0F0F0 or the assertion of hardware reset signal.
•  Device identification mode
  The device will be in device identification mode after boot operation mode is finished or if host
  and/or device does not support boot operation mode. The device will be in this mode, until the SET_RCA command (CMD3) is received.
•  Interrupt mode Host and device enter and exit interrupt mode simultaneously. In interrupt mode there is no data transfer. The only message allowed is an interrupt service request from the device or the host.
•  Data transfer mode The device will enter data transfer mode once an RCA is assigned to it. The host will enter data transfer mode after identifying the device on the bus.
•  Inactive mode The device will enter inactive mode if either the device operating voltage range or access mode is not valid. The device can also enter inactive mode with GO_INACTIVE_STATE command (CMD15). The device will reset to Pre-idle state with power cycle.
  

1.1 eMMC系统概述

1.2 eMMC 的整体架构如下图片所示：

eMMC 内部主要可以分为 Flash Memory、Flash Controller 以及 Host Interface 三大部分。

2 Flash Memory

flash是一种非易失的存储器，其存储结构如下所示：

The embedded device also offers the host the possibility to configure additional local memory partitions with independent address spaces, starting from logical address 0x00000000, for different usage models.
Therefore the memory block areas can be classified as follows:
 Two Boot Area Partitions, whose size is multiple of 128 KB and where booting from e•MMC can be performed.
 One RPMB Partition accessed through a trusted mechanism, whose size is defined as multiple of 128 KB.
 Four General Purpose Area Partitions to store sensitive data or for other host usage models, whose sizes are a multiple of a Write Protect Group.

Each of the General Purpose Area Partitions can be implemented with enhanced or extended
technological features (such as better reliability) that distinguish them from the default storage media. If the enhanced storage media feature is supported by the device, boot and RPMB Area Partitions shall be implemented as enhanced storage media by default.