Disaster Recovery
Today's Flash ROM chips are highly reliable once data have been written successfully. If you do not write to the chips, most manufacturers guaranteed that their chips have data retention for more than 10 years. However, the seeming perfect reliability is basing on data have been successful written. What they didn't specify is the failure rate of writing itself. It does exist, though quite low.
In the embedded computer world, unfortunately, we need to update the contents of Flash so frequently, for example, writing to JFFS2 disk and firmware updating. Writing data to Flash is where most troubles come from.
If, for some reason, portion of the flash ROM corrupts, and the uClinux can not start normally. As long as the boot loader is still alive, we can use it to recover from disasters. The bootloader is network-ready and has a built-in TFTP server. Normally, to restore a 8 MB ROM image, it takes only 2.5 minutes.
Alternatively, using XMODEM 256/1K protocols on low speed serial interface is also supported, though it is not recommended for its poor performance (15 minutes for downloading 8 MB ROM image).
Debug Monitor
Connect to the serial console
Connect to the device with terminal emulation software, e.g. Hyper Terminal, and a RS232 cable, at 115200,n,8,1.
Connect the device to network.
The boot loader is network-ready. Files and images can be downloaded via TFTP.
Enable debug mode.
Set the hardware jumper to enable debug mode.
Reset the device
Reset or power off/on the device. The following messages will be shown on the terminal:
Enter debug monitor
Press ESC to enter debug monitor
|
Metavert
Bootloader SDRAM:
16 MB CFI
Flash ROM found, total 8192 KB Region
#1 64 KB, 8 KB/sector Region
#2 8128 KB, 64 KB/sector Serial
Number: 3D820240 Press
ESC to enter debug mode . Commands: XF Xmodem flash programming LS List
images in flash CLEAR Clear
MTD user disk IP Set IP
address Q
Quit >
IP = 10.0.0.29 (assigned by DHCP server) |
Restore System by TFTP
TFTP
Client Software
The TFTP client is available on both Windows and linux platforms:
Windows: built-in command
tftp –i [ip_address] put [file_name]
linux: The package ‘tftp-hpa’ needs to be installed
tftp –m octet [ip_address] –c put [file_name]
Supported
File Types
While receiving files from the TFTP client, the boot loader uses the file name to determine which operation should be performed:
|
File Name |
Operation |
|
bootloader.bin |
Update the boot loader in the 0-0x10000 preserved block. |
|
linux* |
Update the linux kernel. |
|
romfs* |
Update the rom file system. |
|
*.bin |
Other files with .bin suffix are treated as raw ROM images. |
Examples
Restore ROM Image
Windows: tftp –i 192.168.0.123 put ROM.bin
linux: tftp –m octet 192.168.0.123 –c put ROM.bin
Update linux
kernel
Windows: tftp –i 192.168.0.123 put linux.zip
linux: tftp –m octet 192.168.0.123 –c put linux.zip
Update rom
file system
Windows: tftp –i 192.168.0.123 put romfs.zip
linux: tftp –m octet 192.168.0.123 –c put romfs.zip
Update boot loader
Windows: tftp –i 192.168.0.123 put bootloader.bin
linux: tftp –m octet 192.168.0.123 –c put bootloader.bin
Restore System by XMODEM
The boot loader supports XMODEM 256 and XMODEM 1K protocols. Though still very slow, the later, XMODEM 1K is slightly faster than the former. If network interface is available, it is recommended to restore system by TFTP which is much faster than the serial interface.
There are three types of downloading:
XF All Update the whole image except the 0-0x10000 block.
XF linux Update the linux kernel
XF romfs Update the rom file system
Command Reference
XF
The XF command can transfer files to memory with XMODEM protocol and write them to FLASH ROM.
|
>
XF Usage:
XF [all | linux | romfs] all = update entire ROM linux =
update linux kernel only romfs =
update ROM file system only > |
LS
The LS command lists the images in the flash
|
>
ls romfs.zip 557 KB @0x0f0000 linux.zip 757 KB @0x020000 > |
CLEAR
The CLEAR command clears the user MTD disk (formatting)
|
>
clear Erase
MTD area ? Y/N [ ] Erasing ................................ ................................ ................................ ....... MTD
area erased > |
IP
The IP command sets the device’s IP address manually. This command is optional. Normally, the device will automatically request an IP from the DHCP server, if there’s a DHCP server on the network.
|
>
IP 192.168.0.100 Ok |
Q
The Q command quits the boot loader and proceeds to the normal boot process.
|
>
q Processing
image 6 ... Unzip
image 6 ... Processing
image 7 ... Unzip
image 7 ... Executing
image 7 ... Linux
version 2.4.20-uc0 (metavert@vm-linux) (gcc version 3.0) #651 Wed Nov 25 0 Processor:
Winbond W90P710 revision 1 Architecture:
W90P710 On
node 0 totalpages: 3808 zone(0): 0 pages. zone(1): 3808 pages. zone(2): 0 pages. Kernel
command line: root=/dev/rom0 rw Calibrating
delay loop... 39.83 BogoMIPS Memory:
14MB = 14MB total |