Moxa W325A-LX [61/74] Before programming your embedded system

W315A/325A Linux User's Manual Programmer's Guide

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Before Programming Your Embedded System

Caution Required when Using File Systems

We recommend that you only store your programs on the onboard NOR Flash. The log data generated by your

programs should be stored in an external storage device, such as an SD card or Network File System. Note that

a Network File System will generally provide the largest amount of storage space. In addition, it is easier to

replace a full or damaged SD card than an onboard NOR Flash.

A NOR Flash has a life cycle of 100,000 write operations in the block (128 KB) level, but does not support BBM

(Bad Block Management). An SD card also has a life cycle, but most SD cards are made from a NAND Flash, for

which the hardware controllers implement BBM. This feature allows FAT to skip bad blocks if they exist.

Furthermore, the memory space of an SD card is much larger than that of the NOR Flash. Cautiously utilizing

this space will ensure that its life cycle will not be exceeded. When creating a file for storing log data, we

suggest setting up your program to create a large empty file (e.g., 30 MB), and then write data evenly over the

space. When reaching the end of the space, the program rewinds the write operations. As a result, the number

of write operations on each block will be reduced.

Using a RAM File System instead of a Flash File System

Although data in the RAM file system will be wiped out after a power off, this file system has several advantages

over a Flash file system. The RAM file system includes faster read/write access, and has no life cycle issues.

For timely and/or important applications that relay data directly back to the host, you should write the

necessary log data to the RAM file system. After the host accesses the data, the application will erase the data

to free up the space for further uses.

The embedded computer has limited resources, and for this reason, designers should determine if storing data

in a file system is really necessary. If it is necessary, then be sure to choose the most appropriate file system

for your application.

Flash Memory Map

Partition sizes are hard coded into the kernel binary. To change the partition sizes, you will need to rebuild the

kernel. The flash memory map is shown in the following table.

Address Size Contents

0x00000000 – 0x0003FFFF 256 KB Boot Loader—Read ONLY

0x00040000 – 0x001FFFFF 1.8 MB Kernel object code—Read ONLY

0x00200000 – 0x009FFFFF 8 MB Root file system (JFFS2) —Read ONLY

0x00A00000 – 0x00FFFFFF 6 MB User directory (JFFS2) —Read/Write

Device API

The W315A/325A supports control devices with the ioctl system API. You will need to

include

<moxadevice.h

, and use the following ioctl function.

int ioctl(int d, int request,…);

Input: int d - open device node return file handle

int request – argument in or out

Use the desktop Linux’s man page for detailed documentation:

#man ioctl