Moxa Technologies UC-7420/7410 user manual Journaling Flash File System JFFS2, Software Package

UC-7420/7410 User’s Manual Introduction

services and daemons. During this time, the kernel will start searching for system configuration parameters via rc or inittab.

Normally, the kernel uses the User Root File System to boot up the system. The Mini Root File System is protected, and cannot be changed by the user, providing a “safe” zone. The kernel will only use the Mini Root File System when the User Root File System crashes.

For more information about the memory map and programming, refer to Chapter 5, “Programmer’s Guide.”

Journaling Flash File System (JFFS2)

The User Root File System 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, 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, which enhances the write-life of the devices; native data compression inside the file system design; support for hard links.

The key features of JFFS2 are:

yTargets the Flash ROM Directly

yRobustness

yConsistency across power failures

yNo integrity scan (fsck) is required at boot time after normal or abnormal shutdown

yExplicit wear leveling

yTransparent compression

Although JFFS2 is a journaling file system, this does not preclude the loss of data. The file system will remain in a consistent state across power failures and will always be mountable. However, if the board is powered down during a write then the incomplete write will be rolled back on the next boot, but writes that have already been completed will not be affected.

Additional information about JFFS2 is available at:

http://sources.redhat.com/jffs2/jffs2.pdf

http://developer.axis.com/software/jffs/

http://www.linux-mtd.infradead.org/

Software Package

Boot Loader	Redboot (V1.92)
Kernel	MontaVista embedded Linux 2.4.18
Protocol Stack	ARP, PPP, CHAP, PAP, IPv4, ICMP, TCP, UDP, DHCP, FTP, SNMP
	V1/V3, HTTP, NTP, NFS, SMTP, SSH 1.0/2.0, SSL, Telnet, PPPoE,
	OpenVPN
File System	JFFS2, NFS, Ext2, Ext3, VFAT/FAT

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