User`s manual

ThinkCore IA241/240 Linux User’s Manual Introduction
1-3
AP
API
Protocol
Stack
Device
Driver
Microkernel
User Application
Daemon (Apache, Telnet, FTPD, SNMP)
Application Interface (POSIX, Socket, Secure Socket)
TCP, IP, UDP, CMP, ARP, HTTP, SNMP, SMTP
PCMCIA, CF, WLAN, USB, UART, RTC, LCM, Keypad
Memory control, Schedule, Process
RS-232/422/485, Ethernet, PCMCIA, CompactFlash, USB
File
System
Hardware
OS Kernel
The IA241/240’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 IA241/240 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 IA241/240 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