Before Wang-Wang has written many articles on semiconductor eMMC, there are not enough fans reaction system, this does, Hong Wang semiconductor reference to the article published on the Web, and we systematically share eMMC Flash Memory and relevant.
eMMC is a kind of Flash Memory, before details of eMMC, briefly explain the Flash Memory. Flash Memory is a nonvolatile memory. In embedded systems commonly used to store system, application and data. In the PC system, mainly used in solid-state hard drive and motherboard BIOS. Further, most of the U disk, the SDCard other removable storage devices are also used as the storage medium Flash Memory.
- Key Features of Flash Memory
Compared with a conventional hard disk memory, Hong Wang, ICMAX found Flash Memory semiconductor light weight, low power consumption, small size, and other advantages seismic capability, but there are many limitations, mainly as follows:
You need to erase and then write
certain restrictions when Flash Memory write data. It can only currently rewriting bits 1 to 0, and can not be had to rewrite bits 0 to 1, only the erase operation to rewrite the entire bit is 1.
Block erase a limited number of
Flash Memory for each data block has erased limit the number of times (ranging from 100,000 to 1,000,000 times), erase more than a certain number of times, the data block can not be reliably store data become bad blocks.
In order to prolong the life of Flash Memory maximized, the software needs to be done on the rewritable equalization (Wear Leveling), written by dispersing, using the equalization means of dynamic mapping each data block. At the same time, the software also needs to be a bad block management (Bad Block Management, BBM), to identify bad blocks, not involved in the bad block data storage. (Note: In addition to the bad block erase result, Flash Memory will produce a bad block in the production process, i.e., the inherent bad blocks.)
Write disturbance
due to the physical characteristics of the hardware implementation, Flash Memory when performing read and write operations, may cause the occurrence of the other bits are bits adjacent inverted, resulting in abnormal data. This anomaly can be restored by re-erased. Flash Memory applications typically use algorithms such as ECC error detection and correction data.
Leakage of charge
stored in the charge Flash Memory storage unit, if there is no long-term use, the charge will leak, resulting in data errors, but this a long time, usually ten years or so. Such exceptions are non-permanent, re-erasing can be restored.
- NOR Flash 和 NAND Flash
Hong Wang learned ICMAX semiconductor memory according to different principles of hardware, Flash Memory can be divided into two types of NOR Flash and NAND Flash. The main differences are as follows:
· NAND Flash and NOR Flash read speed is similar, vary depending on the interface;
writing speed · NAND Flash is much faster than NOR Flash;
· NAND Flash erase much faster than NOR Flash;
· NAND Flash maximum rub the Flash times more than the NOR;
· the NOR support execution on the Flash chip, the code can be run directly above;
· the NOR the Flash software driver is simpler than the Flash the NAND;
· the NOR the Flash random data byte read, NAND Flash is required to read in blocks .
· Large-capacity NAND Flash NOR Flash much lower than the cost, the volume is smaller;
(Note: NAND Flash and NOR Flash erase are performed in blocks, performing a program or erase operation, NOR Flash about need 5s, while NAND Flash usually no more than 4ms.)
2.1 NOR Flash
ICMAX semiconductor find Hong Wang, depending on the CPU side NOR Flash interface, it can be divided into Parallel NOR Flash and Serial NOR Flash categories.
Parallel NOR Flash can access the Host to the SRAM / DRAM Controller, the stored content can be directly mapped into the CPU address space does not need to be copied to the RAM access CPU, thus supporting the implementation of on-chip. Serial NOR Flash Flash lower cost than Parallel NOR, mainly through SPI interface Host connection.
Picture: Parallel NOR Flash and Serial NOR Flash
Given the slow erase NOR Flash, higher cost characteristics, NOR Flash is mainly used in small capacity, small scene updates, such as a PC motherboard the BIOS, router system storage.
NOR Flash is more details, please contact ICMAX Wang-Wang semiconductors.
2.2 NAND Flash
NAND Flash need to communicate, as shown by a special NFI (NAND Flash Interface) terminal with the Host:
Picture: NAND Flash Interface
The NAND Flash different number of bits within each memory cell stores can be divided into SLC (Single-Level Cell), MLC (Multi-Level Cell), TLC (Triple-Level Cell) and QLC (Quad-Level Cell) four class. Wherein, in a storage unit, the SLC can store 1 bit, 2 bits can be stored in the MLC, TLC can store three bits, four bits can be stored in the SLC.
Picture: SLC, MLC, TLC and QLC
Hong Wang semiconductor ICMAX found more single bit NAND Flash memory means for storing, reading and writing performance worse, the shorter the life expectancy, but the cost will be lower. Figure above, given the cost and life data and the specific process technology.
(Note: The above data from the Internet, for reference only)
Compared to NOR Flash, NAND Flash write performance, low cost and large capacity. At present, the internal eMMC Flash Memory vast majority of mobile phones and tablet and other mobile devices used belong to NAND Flash. The PC also use SSD NAND Flash.
NAND Flash more details, please contact ICMAX Wang-Wang semiconductors.
- Raw Flash 和 Managed Flash
Due to the presence of Flash Memory erase in blocks, limiting the number of erase, read and write the limitations of interference, charge leakage, etc., in order to maximize the value of play Flash Memory, usually need to have a special software level, realize the bad block management, rub write functional equilibrium, ECC, garbage collection, which is a software layer called FTL (Flash Translation Layer).
In the specific implementation, depending on the location of FTL is located, the Flash Memory can be divided into two categories Raw Flash and Managed Flash.
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