User`s manual

IA260-261-262 EM-2260 LX User’s Manual Introduction
The IA260/IA261/IA262/EM-2260’s built-in Flash ROM is partitioned into Boot Loader, Linux
Kernel, Root File System, and User directory partitions.
In order to prevent user applications from crashing the Root File System, the
IA260/IA261/IA262/EM-2260 uses a specially designed Root File System with Protected
Configuration for emergency use. This Root File System comes with serial and Ethernet
communication capability for users to load the Factory Default Image file. The user directory
saves the user’s settings and application.
To improve system reliability, the IA260/IA261/IA262/EM-2260 has a built-in mechanism that
prevents the system from crashing. When the Linux kernel boots up, the kernel will mount the root
file system for read-only, and then enable services and daemons. During this time, the kernel will
start searching for system configuration parameters via rc or inittab.
Normally, the kernel uses the Root File System to boot up the system. The Root File System is
protected, and cannot be changed by the user. This type of setup creates a “safe” zone.
For more information about the memory map and programming, refer to Chapter 5, Programmer’s
Guide.
Journaling Flash File System (JFFS2)
The Root File System and User directory in the flash memory is formatted with the Journaling
Flash File System (JFFS2). The formatting process places a compressed file system in the flash
memory. This operation is transparent to the user.
The Journaling Flash File System (JFFS2), which was developed by Axis Communications in
Sweden, puts a file system directly on the flash, instead of emulating a block device. It is designed
for use on flash-ROM chips and recognizes the special write requirements of a flash-ROM chip.
JFFS2 implements wear-leveling to extend the life of the flash disk, and stores the flash directory
structure in the RAM. A log-structured file system is maintained at all times. The system is always
consistent, even if it encounters crashes or improper power-downs, and does not require fsck (file
system check) on boot-up.
JFFS2 is the newest version of JFFS. It provides improved wear-leveling and garbage-collection
performance, improved RAM footprint and response to system-memory pressure, improved
concurrency and support for suspending flash erases, marking of bad sectors with continued use of
the remaining good sectors (enhancing the write-life of the devices), native data compression
inside the file system design, and support for hard links.
The key features of JFFS2 are:
y Targets the Flash ROM Directly
y Robustness
y Consistency across power failures
y No integrity scan (fsck) is required at boot time after normal or abnormal shutdown
y Explicit wear leveling
y Transparent compression
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