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   首页>技术专栏>Nand Flash专栏>Flash Management Software:When, Why and Which?

Flash Management Software:When, Why and Which?

文档内容介绍:
文档名称 :Flash Management Software:When, Why and Which?
文档格式 :pdf
发 布 者 :M-Systems
语  言 :英文
更新日期 :2007-9-20
本文档共9页。
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内容简介 :
INTRODUCTION
It is a well-known fact that in order to use flash memory, a software driver is required. But the “when, why and which” of flash management software is far more obscure. The purpose of this article is to shed some light on different limitations of flash that require software management, to describe system level considerations, and to review popular alternatives used today.

IS SOFTWARE ALWAYS NEEDED TO WORK WITH FLASH?
Many developers will probably say that software is not needed. And they’ll be mostly right. The simple fact is that when flash memory is used to run code that is never changed, as is the case with most embedded devices (Did you ever update your VCR’s firmware or your digital camera’s? …), flash, or rather NOR flash, can indeed be regarded as any other standard memory that does not require software.
If only life could be so simple.
Fact: If the only requirement is to run code and never change it, you would use ROM. It’s much cheaper, and probably much faster. But if you choose to use flash, it is probably because you want the option of erasing it (or rather parts of it) in a “flash” and changing its content.
Fact: To write information to an area of standard memory that already contains information, all you need to do is, simply enough, re-write it. However, before you write information to an area in flash that is filled (even partially) with content, you must first erase it. This “erase first” requirement means that you need a software driver to perform even a basic write operation in order to verify if the area to which you want to write contains information and requires erasing.
Fact: NAND flash (common in data-centric applications) has an I/O interface and uses a protocol that includes commands (read/write/erase), address and data. NAND also does not permit access to a random memory address. Instead, you must access pages of 512Bytes at a time.
This means that a software driver is required to perform ANY type of access to NAND flash. This also means that although raw NAND flash is very convenient as a disk replacement (mechanical hard drives are also accessed in blocks of 512 Bytes, and are referred to as “block devices”), you cannot run code from it. This simple, low-level software module performing read, write and erase operations is often referred to as the MTD or Memory Technology Driver........

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