一、首先得分清楚几个基本概念：

     1、文件系统

  文件系统是操作系统用于明确存储设备（常见的是磁盘，也有基于NAND Flash的固态硬盘）或分区上的文件的方法和数据结构；

即在存储设备上组织文件的方法。操作系统中负责管理和存储文件信息的软件机构称为文件管理系统，简称文件系统。文件系统由三部

分组成：文件系统的接口，对对象操纵和管理的软件集合，对象及属性。从系统角度来看，文件系统是对文件存储设备的空间进行组织

和分配，负责文件存储并对存入的文件进行保护和检索的系统。具体地说，它负责为用户建立文件，存入、读出、修改、转储文件，控

制文件的存取，当用户不再使用时撤销文件等。

　　嵌入式系统中常用的文件系统包括：jffs2、squashfs、ubifs、initramfs、nfs、、、、jffs2是最常用的日志文件系统，ubifs是

属于下一代jffs2，initramfs用于验证kernel是否正常运行，squashfs是一种压缩型文件系统，所占空间要比jffs2小一半，它通过解压

缩文件系统后，创建新分区rootfs_data，通过overlay（需要内核patch支持）文件系统挂载新分区到jffs2上，从而实现可写。使用相

应的文件系统需要相应的内核配置支持。

     各文件系统的制作：

     jffs2：：

     ubifs：：

     suqashfs：：

     initramfs：

　　其中offset是分区开始的偏移地址，MTDPART_OFS_APPEND，表示紧接着上一个分区，

     MTD Core会自动计算和处理分区地址；size是分区的大小，在最后一个分区我们设为

  MTDPART_SIZ_FULL，表示这个NAND剩下的所有部分。这样配置NAND的分区并不是唯

  一的，需要视具体的系统而定，我们可以在kernel中这样显式的指定，也可以使用bootloader

  传给内核的参数进行配置。

     2、内核

     kernel的几种格式：

     vlinux：

     vlinuxz：

     image：

     uImage.img:

     3.uboot

     几个重要的uboot启动参数：

     bootargs：

     bootcmd：

二、BCM特有的bootloader--CFE基本操作：

Decompressing...done
Found a ST compatible serial flash with 256 64KB blocks; total size 16MB

CFE version 6.30.163.2002 (r382208) based on BBP 1.0.37 for BCM947XX (32bit,SP,)
Build Date: Thu Feb 28 22:09:40 EST 2013 (root@localhost.localdomain)
Copyright (C) 2000-2008 Broadcom Corporation.

Init Arena
Init Devs.
Boot partition size = 262144(0x40000)
DDR Clock: 400 MHz
Warning: using legacy sdram_ncdl parameter to set DDR frequency. Equivalent setting in clkfreq=800,*0* will be ignored.
et0: Broadcom BCM47XX 10/100/1000 Mbps Ethernet Controller 6.30.163.2002 (r382208)
CPU type 0x0: 800MHz
Tot mem: 262144 KBytes

CFE mem: 0x00F00000 - 0x00FDA500 (894208)
Data: 0x00F4EB5C - 0x00F4F014 (1208)
BSS: 0x00F4F020 - 0x00F74500 (152800)
Heap: 0x00F74500 - 0x00FD8500 (409600)
Stack: 0x00FD8500 - 0x00FDA500 (8192)
Text: 0x00F00000 - 0x00F44874 (280692)
Boot: 0x00FDB000 - 0x0101B000
Reloc: I:00000000 - D:00000000

Device eth0: hwaddr 00-90-4C-0F-F0-01, ipaddr 192.168.1.1, mask 255.255.255.0
gateway not set, nameserver not set
Loader:raw Filesys:tftp Dev:eth0 File:: Options:(null)
Loading: Failed.

CFE> printenv
Variable Name Value
-------------------- --------------------------------------------------
BOOT_CONSOLE uart0
CFE_VERSION 1.0.37
CFE_BOARDNAME BCM947XX
CFE_MEMORYSIZE 262144
NET_DEVICE eth0
NET_IPADDR 192.168.1.1
NET_NETMASK 255.255.255.0
NET_GATEWAY 0.0.0.0
NET_NAMESERVER 0.0.0.0
STARTUP go;
*** command status = 0

CFE> help
Available commands:

nvram NVRAM utility.
reboot Reboot.
set console Change the active console device
loop Loop a command
flash Update a flash memory device
memtest Test memory.
f Fill contents of memory.
e Modify contents of memory.
d Dump memory.
u Disassemble instructions.
batch Load a batch file into memory and execute it
go Verify and boot OS image.
boot Load an executable file into memory and execute it
load Load an executable file into memory without executing it
save Save a region of memory to a remote file via TFTP
ping Ping a remote IP host.
arp Display or modify the ARP Table
ifconfig Configure the Ethernet interface
show clocks Show current values of the clocks.
show heap Display information about CFE's heap
show memory Display the system physical memory map.
show devices Display information about the installed devices.
unsetenv Delete an environment variable.
printenv Display the environment variables
setenv Set an environment variable.
help Obtain help for CFE commands

For more information about a command, enter 'help command-name'
*** command status = 0
CFE>
CFE> help flash

SUMMARY

Update a flash memory device

USAGE

flash [options] filename [flashdevice]
Copies data from a source file name or device to a flash memory device.
The source device can be a disk file (FAT filesystem), a remote file
(TFTP) or a flash device. The destination device may be a flash or eeprom.
If the destination device is your boot flash (usually flash0), the flash
command will restart the firmware after the flash update is complete

OPTIONS

-noerase Don't erase flash before writing
-offset=* Begin programming at this offset in the flash device
-size=* Size of source device when programming from flash to flash
-noheader Override header verification, flash binary without checking
-mem Use memory as source instead of a device

*** command status = 0
CFE>
CFE>
CFE> help load

SUMMARY

Load an executable file into memory without executing it

USAGE

load [-options] host:filename|dev:filename
This command loads an executable file into memory, but does not
execute it. It can be used for loading data files, overlays or
other programs needed before the 'boot' command is used. By
default, 'load' will load a raw binary at virtual address 0x20000000.

OPTIONS

-elf Load the file as an ELF executable
-srec Load the file as ASCII S-records
-raw Load the file as a raw binary
-z Load compessed file
-loader=* Specify CFE loader name
-tftp Load the file using the TFTP protocol
-fatfs Load the file from a FAT file system
-rawfs Load the file from an unformatted file system
-fs=* Specify CFE file system name
-max=* Specify the maximum number of bytes to load (raw only)
-addr=* Specify the load address (hex) (raw only)

*** command status = 0
CFE>
CFE> load tftp 192.168.1.10:Image
*** command status = -6
CFE>
CFE> load -tftp -addr=81008000 192.168.1.10:Image
Loader:raw Filesys:tftp Dev:eth0 File:192.168.1.10:Image Options:(null)
Loading: .. 6566180 bytes read
Entry at 0x81008000
*** command status = 0
CFE>
CFE>
CFE> help go

SUMMARY

Verify and boot OS image.

USAGE

go
Boots OS image if valid. Waits for a new OS image if image is invalid
or boot_wait is unset or not on.

*** command status = 0
CFE>

CFE> load -addr=82000000 -tftp 192.168.1.10:u-boot.bin
Loader:raw Filesys:tftp Dev:eth0 File:192.168.1.10:u-boot.bin Options:(null)
Loading: .. 537212 bytes read
Entry at 0x82000000
*** command status = 0
CFE>

CFE> show devices
Device Name Description
------------------- ---------------------------------------------------------
uart0 NS16550 UART at 0x18000300
uart1 NS16550 UART at 0x18000400
flash0 ST Compatible Serial flash size 16384KB
flash0.boot ST Compatible Serial flash offset 00000000 size 256KB
flash0.trx ST Compatible Serial flash offset 00040000 size 1KB
flash0.os ST Compatible Serial flash offset 0004001C size 16064KB
flash0.nvram ST Compatible Serial flash offset 00FF0000 size 64KB
flash1.boot ST Compatible Serial flash offset 00000000 size 256KB
flash1.trx ST Compatible Serial flash offset 00040000 size 16064KB
flash1.nvram ST Compatible Serial flash offset 00FF0000 size 64KB
eth0 Broadcom BCM47XX 10/100/1000 Mbps Ethernet Controller
*** command status = 0
CFE>

CFE> flash -noheader 192.168.1.10:u-boot.bin -offset=0 flash0
Reading 192.168.1.10:u-boot.bin: Done. 537212 bytes read
Programming...done. 537212 bytes written
*** command status = 0
CFE>