I was working with 1.1 version of this router. first of all I installed openwrt-ar71xx-generic-tl-wa701n-v1-squashfs-factory.bin firmware in it. it was working. but when I re flashed it with openwrt-ar71xx-generic-tl-wa701n-v1-jffs2-sysupgrade.bin it stopped at a point during flashing. since i lost connection with it.
I tried failsafe and was able to log into fail safe. it if accessible through telnet, but while changing password it is saying cannot create /modify a file as no space on device. so scp can not start. is there any way to revive it/re flash it? I don't have any serial cable.

During failsafe, the root partition is mounted read-only, so you can write to it

You can only write into /tmp, which is a ramdisk.

The failsafe mode purpose is to reflash a working firmware using /tmp as temporary storage.

Put the working "openwrt-ar71xx-generic-tl-wa701n-v1-squashfs-factory.bin" file at the root of a webserver on your PC, then:

# cd /tmp
# wget http://your_pc_ip_address/openwrt-ar71xx-generic-tl-wa701n-v1-squashfs-factory.bin
# mtd -r write openwrt-ar71xx-generic-tl-wa701n-v1-squashfs-factory.bin firmware
# reboot -f

This should put you back on tracks!

or if you manage to get the AP online for example with:

ifconfig eth0 192.168.1.2
route add default gw 192.168.1.1
echo "nameserver 8.8.8.8">/etc/resolv.conf

then you can

cd /tmp
wget http://downloads.openwrt.org/attitude_adjustment/12.09-rc1/ar71xx/generic/openwrt-ar71xx-generic-tl-wa701n-v1-squashfs-factory.bin
mtd -r write openwrt-ar71xx-generic-tl-wa701n-v1-squashfs-factory.bin firmware
reboot -f

Dear friend nebbia88, It really Worked. the router is now back on track.
should I put the jffs2 firmware over it or run the sqashfs firmware?

With jffs2, you don't have failsafe mode, whereas it is present in squashfs.

In jjfs2 mode, you only have a single r/w jffs2 partition, where you can actually remove installed packages. But no failsafe as you can destroy everything

In sqashfs mode, you have both a r/o squashfs partition and a jffs2 partition. You can mark the packages as "removed", but they are still present in Flash memory if they were on the squashfs partition, you cannot reclaim space. But you have failsafe mode available.

If unsure, choose the squashfs type!

Just to summarise Squonk's post:
DO NOT USE JFFS unless you have friends to drink lots of alcohol and forget you ever had a router. Or you are an openWRT guru.

... with a serial UART to USB adapter and a soldering iron

yea, that would do it!

701ND is my first TP-LINK board that I success  porting UBNT airOS firmware a.k.a openwrt Kamikaze 8.09 by upgrading the flash chip size to 8MiB and putting XM series u-boot on flash chip the rest finished by tftp-ing XM image to router.

=~=~=~=~=~=~=~=~=~=~=~= PuTTY log 2013.02.22 22:15:34 =~=~=~=~=~=~=~=~=~=~=~=
øð>C¡H¨Õ½½Ñ1.1.4.2-s564 (Jul 19 2012 - 10:41:56)

Board: Ubiquiti Networks XM board (rev 0.1 a091)
DRAM: 8 MB
WLAN Module found (#1).
Net:   No valid address in Flash. Using fixed address
No valid address in Flash. Using fixed address

Hit any key to stop autoboot:  1  


## Booting image at 9f050000 ...
   Image Name:   MIPS Ubiquiti Linux-2.6.15--LSDK
   Created:      2010-02-09  16:41:08 UTC
   Image Type:   MIPS Linux Kernel Image (lzma compressed)
   Data Size:    755831 Bytes = 738.1 kB
   Load Address: 80002000
   Entry Point:  80002000
   Verifying Checksum ...Kernel Image ... 
Starting kernel ...

Booting...
init done

(Last edited by xopal on 22 Feb 2013, 16:49)

my friend, thanks a lot !