RAM 6.0 BUX II Series Guía de usuario descargar pdf (Pagina 29)

8. Flash Devices and Flash File System Support

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Localizes Static File Blocks.

Localizing blocks that belong to static files significantly facilitates transferring

these blocks when the wear-leveling algorithm decides to move static areas.

Read and Write Operations

One of the characteristics of flash memory that differs considerably from the more

common magnetic-medium mechanical disks is the way in which it writes new

data to the medium. When using traditional magnetic storage media, writing new

data to a previously written storage area simply overwrites the existing data,

essentially obliterating it; whereas flash does not. This section describes how flash

reads from, and writes to, memory.

Reading from Blocks

Reading the data from a block is straightforward. The file system requests the

contents of a particular block. In response, TrueFFS translates the block number

into flash memory coordinates, retrieves the data at those coordinates, and returns

the data to the file system.

Writing to Previously Unwritten Blocks

Writing data to a block is straightforward, a byte can only be written once before it

is erased. Therefore, if the target block has remained unwritten since the last erase

of the block, the write process is simple. TrueFFS translates the block number into

flash memory coordinates and writes to the location. However, if the write request

seeks to modify the contents of a previously written block, the situation is more

complex.

If any write operation fails, TrueFFS attempts a second write. For more

information, see Recovering During a Write Operation, p.29.

Writing to Previously Written Blocks

If the write request is to an area of flash that already contains data, TrueFFS finds

a different, writable area of flash instead—one that is already erased and ready to

receive data. TrueFFS then writes the new data to that free area. After the data is

safely written, TrueFFS updates its block-to-flash mapping structures, so that the

NOTE: Storing data in flash memory requires the use of a manufacturer-supplied

programming algorithm, which is defined in the MTD. Consequently, writing to

flash is often referred to as programming flash.

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RAM 6.0 BUX II Series Guía de usuario Pagina 29