User`s manual

Moxa C Programmable RTU Controllers Introduction
1-3
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 users.
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.ative data compression inside the file system design, and support for hard links.
The key features of JFFS2 are:
• Targets the Flash ROM Directly
• Robustness
• Consistency across power failures
• No integrity scan (fsck) is required at boot time after normal or abnormal shutdown
• Explicit wear leveling
• Transparent 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 system 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 Moxa Boot Loader (v1.2)
Kernel Linux 2.6.9
Protocol Stack ARP, PPP, CHAP, PAP, IPv4, ICMP, TCP, UDP, DHCP, FTP, HTTP, NTP, NFS, SMTP, SSH
1.0/2.0, SSL, Telnet, PPPoE, OpenVPN
File System JFFS2, NFS, Ext2, Ext3, VFAT/FAT
OS shell command Bash
Busybox Linux normal command utility collection
Utilities
tinylogin Login and user manager utility
telnet Telnet client program
ftp FTP client program
smtpclient Email utility
scp Secure file transfer Client Program
Daemons
pppd Dial in/out over serial port daemon
telnetd Telnet server daemon