These are the commands for the serial console to recover an otherwise bricked device when doing firmware development. You will need to download the recovery version of the firmware and have those files in the correct directory in your ftp server for it to work.
You need a ftp or tftp server running and a static ip of 192.168.1.2 or 192.168.1.10 ip address on the server running the ftp server.
For serial connection to work, set the baud rate to 115200, data bits 8, parity: None Stop bits:1
Hit any key during bootup to stop the regular boot process and get into recovery mode. You will know you are in recovery mode when you see the prompt represented as: ath> Instead of the usual: root@anonabox:/#
Paste the following commands into the serial terminal in order. After the last command is entered the device will boot itself up.
tftpboot 0x81000000 openwrt-ar71xx-generic-ap143-16M-kernel.bin
erase 0x9fe80000 +0x130000
cp.b 0x81000000 0x9fe80000 0x130000
tftpboot 0x81000000 openwrt-ar71xx-generic-ap143-16M-rootfs-squashfs.bin
erase 0x9f050000 +0x800000
cp.b 0x81000000 0x9f050000 0x800000