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After re-deploying the Ubiquiti Unifi UAP-Pro at the new base-camp, it simply didn't work anymore. No DHCP reaction, nothing. Except for the LED blinking white sometimes, it seemed completely broken. After opening and attaching a terminal to the serial console, the boot output didn't look promising but at least it wasn't completely dead.

U-Boot unifi-v1.2.3.74-ge597862a (Mar 14 2013 - 18:30:11)

Board: Ubiquiti Networks AR9344 board (e507-27.2122.0030.0030)
DRAM:  128 MB
Flash: 16 MB
Net:   eth0
Hit any key to stop autoboot:  0
Scanning JFFS2 FS: .| 
Unknown node type: e008 len 52 offset 0xf41eec
[...]                                                                                                                                       done.
cant find .firewall.uci-mWgTyx��
[...]
cant find .wireless.uci-HxpWh9
cant find .network.uci-anmaB1
�����������������������������������������������������������������������
�����������������������������������������������������������������������
�����������������������������������������������������������������������
�������������������������������������������������������

It is still unclear what exactly causes this jffs2 corruption, but there have been at least three other reported cases and one directly confirmed by djs500, who found the draft-wip-template for this mission log on the net, had exactly the same problem and came back with positive feedback that he was able to fix it using Solution 3, as we did too.

https://community.ubnt.com/t5/UniFi-Troubleshooting/UniFi-TFTP-soft-recovery-for-bricked-access-point/ta-p/607605

Set a static IP on your PC's NIC from 192.168.1.0/24 range, but not 192.168.1.20 (this is the Unifi AP default TFTP IP).

Follow the steps to unbrick your UAP:

1. Set the IP on your PC to be able to access the bricked unit and prepare the firmware file.
2. On your PC, open your TFTP client and locate the firmware.bin file so you can start it later. Do not initiate the transfer.

Using the Windows integrated TFTP client the command to prepare is: “tftp -i 192.168.1.20 PUT [path to file]\firmware.bin” Unplug the bricked unit. Plug the LAN connection of the PoE injector directly to your PC's NIC. Keep the UniFi AP's reset button depressed and plug in network/PoE in the unit. Keep the reset button depressed until you see the light cycling relatively fast through amber/green/off colors (~14 seconds from power on) → Release it. Now the device is in TFTP transfer mode. Engage the TFTP push command and wait. The device will write the firmware and it will reboot. If you wait too long to start the TFTP transfer, the push will not work as the device will stall. Please redo from step 3. To ensure all goes clean, after the device gets stable (blinking or steady amber LED), give it a reset: Remove power. Reconnect holding the reset button for ~7 seconds (green led will flash once) → release reset button and wait for the device to stabilize again. After device is stabilized, power cycle it again, and you are good to go on adopting the device in the controller again.

This may be due to the fact that it expects a bricked UBNT firmware and NOT an OpenWRT installation.

Soft Unbrick via Serial using urescue and a tftp server was another method mentioned somewhere, but sadly it never really flashed anything and went staight to the reset in less than a second instead. It could never have written the complete firmware in this short time period and after testing: it didn't, so “Firmware update complete” was a lie:

ar7240> urescue
Setting default IP 192.168.1.20
Starting TFTP server...
Using eth0 (192.168.1.20), address: 0x81000000
Waiting for connection: -
Receiving file from 192.168.1.254:39067
Received 4683453 bytes
Firmware Version: BZ.ar934x.v3.2.1.2601.140606.1622
Setting U-Boot environment variables
Will not overwrite u-boot partition! Skipped.

Firmware update complete.

Resetting..

None of the above solutions worked with our OpenWRT UAP-Pro, so we had to grab one of the original jffs2 images from a live one with original UBNT firmware and use a tftp server to transfer that jffs2 image file to the AP and write the image by hand, which finally worked.

The following unbrick trace documents the 9 easy to follow steps codec, fpletz and I took to restore the UAP to its orginal UBNT firmware with default configuration (and default ubnt login) to be able to finally reinstall OpenWRT.

Just bunzip2 the downloaded jffs2.img.bz2 and put jffs2.img into your tftproot so that the AP can access it via LAN. If you don't know which tftp-server to pick, dnsmasq and atftp have been reliable alternatives and have a solid base of documentation and HOWTOs to get started out there.

In this setup dnsmasq was hosted on a laptop, eth0 IP 192.168.1.254 connected via LAN to the main port of the UAP-Pro.

image: ttl-serial-connection-info

Power up the AP and press a key to enter u-boot menu, then transfer and load the original firmware-image over tftp to memory address 0x83000000:

ar7240> tftp 83000000 jffs2.img

If the tftp server is reachable, the output should look like this:

Using eth0 device
TFTP from server 192.168.1.254; our IP address is 192.168.1.20
Filename 'jffs2.img'.
Load address: 0x83000000
Loading: #################################################################
         #################################################################
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         #############################
done
Bytes transferred = 16121856 (f60000 hex)

The firmware image is stored in RAM now and occupies f60000 bytes. Writing it from there to flash memory may fail when the target area has not been erased or if it is write-protected. Let's take cae of that first.

This gives you an overview of the partition table layout

ar7240> mtdparts

device nor0 <ath-nor0>, # parts = 5
 #: name                        size            offset          mask_flags
 0: u-boot                      0x00040000      0x00000000      0
 1: u-boot-env                  0x00010000      0x00040000      0
 2: jffs2                       0x00f60000      0x00050000      0
 3: cfg                         0x00040000      0x00fb0000      0
 4: EEPROM                      0x00010000      0x00ff0000      0

active partition: nor0,0 - (u-boot) 0x00040000 @ 0x00000000

defaults:
mtdids  : nor0=ath-nor0
mtdparts: mtdparts=ath-nor0:256k(u-boot),64k(u-boot-env),15744k(jffs2),256k(cfg),64k(EEPROM)

Reset partition table to defaults with

ar7240> mtdparts default

Save environment changes:

ar7240> saveenv

Saving Environment to Flash...
Un-Protected 1 sectors
Erasing Flash.... done
Erased 1 sectors
Writing to Flash... write addr: 9f040000
done
Protected 1 sectors

Now it is time to make sure that any write-protection is disabled:

ar7240> protect off all

Un-Protect Flash Bank # 1

Figuring out the correct address and length was a bit difficult, uncertain, not well documented and took us quite a while, because we didn't want to brick it more by writing stuff somewhere other than we intended. Unfortunately, there was no documentation about the process of how we derived at that conclusion, but in the end we finally decided to start at address 0x9f050000 for the length of the jffs2 image as indicated by the tftp transfer (0xf60000) and the mtd partition size (0xf60000)

ar7240> erase 0x9f050000 +0xf60000

...................................................................................................................................................................................................................................................... done
Erased 246 sectors

The cp command knows about flash memory areas and will automatically invoke the necessary flash programming algorithm when the target area is in flash memory.

ar7240> cp.b 0x83000000 0x9f050000 0xf60000

Copy to Flash... write addr: 9f050000
done

Since we still have the ubnt jffs2 image stored in RAM we can comfortably byte-compare the content starting at address 0x83000000 (RAM) and the content of address 0x9f050000 (Flash) for the length of 0xf60000. Both have to match, otherwise something obviously went wrong during the flashing process.

ar7240> cmp.b 0x83000000 0x9f050000 0xf60000

Total of 16121856 bytes were the same

ar7240> reset

Resetting...

U-Boot unifi-v1.2.3.74-ge597862a (Mar 14 2013 - 18:30:11)

Board: Ubiquiti Networks AR9344 board (e507-27.2122.0030.0030)
DRAM:  128 MB
Flash: 16 MB
Net:   eth0
Hit any key to stop autoboot:  0
Scanning JFFS2 FS: . done.
## Booting image at 81000000 ...
   Image Name:   MIPS Ubiquiti Linux-2.6.32.33
   Created:      2014-06-06  23:26:31 UTC
   Image Type:   MIPS Linux Kernel Image (lzma compressed)
   Data Size:    4450109 Bytes =  4.2 MB
   Load Address: 80002000
   Entry Point:  80002000
   Verifying Checksum at 0x81000040 ...OK
   Uncompressing Kernel Image ... OK

Starting kernel ...

When you are done with your draft, enter the following URL schema, create the page (with current date and your title) and copy the content into it:

https://apollo.open-resource.org/mission:log:2013:09:24:title-of-mission-log