1.1 diag mode
如果用tftp連不上，就要把進入diag mode的流程多試幾次，因為那代表沒有成功進行diag mode
下面是openwrt網站中找出來的操作方式，不過因為我慧根不夠，沒有試成功。
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Using diag mode
To install OpenWrt using TFTP or the ASUS firmware restoration tool you have to put the router in diag mode. To put the router in the diag mode, do this:
Unplug the router's power cord.
Confirm your PC is configured to request an address via DHCP.
Connect the router's LAN1 port directly to your PC.
Push the black RESTORE button using a pen or such, and keep the button pushed down.
Plug the power on while keeping the RESTORE button pushed for few seconds.
When you see a slowly blinking power light, you are in diag mode.
Now the router should accept an image via TFTP or via the ASUS firmware restoration tool.
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tftp 192.168.1.1
tftp> binary
tftp> trace
tftp> put openwrt-brcm-2.4-squashfs.trx
1.2.failover mode
這是我測試時實際生效的方式，上面第一個方式我並沒有測成功
開機時按reset紐，進入電源燈快閃模式，此時可用telnet直接連進機器，不用密碼就是root
這本來是用來忘記密碼時，reset密碼用的，我卻是拿來重裝OS
在telnet後，打下面的指令下載並把image檔「安裝」好，只要兩個指令就解決了。
wget http://downloads.openwrt.org/kamikaze/7.09/brcm-2.4/openwrt-brcm-2.4-squashfs.trx
mtd write openwrt-brcm-2.4-squashfs.trx linux && reboot
