Flash File System

Flash memory is widely used to hold a file system for an embedded device. The following is some facts about flash file system:
  • Flash has two types: NAND and NOR flash. NOR is expensive and allows random-access for reading, NAND is cheap and allows only page access.
  • Flash memory has finite number of erase/write cycles. >100K
  • Flash devices allow programming values from a “1” to a “0”, but not from “0” to a “1” value. To program values back to “1”s requires erasing a full block. The time taken to erase blocks can be significant. In most cases when data is edited it must be written to a new location in flash and the old data invalidated. (Wear levelling)
  • Flash file system types: JFFS2 and YAFFS.
  • Flash file system contains of both code and data. There are two ways to execute the code: Store and Download (SnD) and eXecute in Place (XiP).
SnD (upper) and XiP (lower)

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