So, I just botched a firmware update on one of my PowerLine couplers. The model I had trouble with is a TP-Link TL-PA4020P. However, this quick guide should work with pretty much any Atheros-based PLC device.
Steps to Reproduce
- Download manufacturer’s setup tool
- Download firmware files (“nvm” and “pib” files)
- Refrain from directly connecting the PLC to the computer, instead leave it hooked up to a switch and other hardware.
- Start firmware update using the aforementioned setup tool
- Have a bit of bad luck
- “Firmware Upgrade failed” error message.
- Next up, “Local device not connected” error message.
- After unplugging and re-plugging the PLC, no lights light up.
- Faint hissing from the device, in normal operation it is silent.
OK, keep calm. This is a modern piece of hardware, surely it wouldn’t need to be disassembled to flash a firmware. Right? Or so my hopes went as I started panicking. Looks like I’m not getting the manufacturer tool to retry the update on the (hopefully just) soft-bricked device. That piece of software only tells me that it can’t find the local device. A quick web search (“TP-Link PowerLine failed firmware fix” and similar) didn’t come up with anything good right away.
Well then, I thought, let’s see if it gives off any signs of life. I directly connected the PLC to my trusty MacBook and fired up WireShark. When the first packets started appearing I breathed a sigh of relief. The PLC still manages to get an ethernet link up. Amidst the stuff the Mac fires off when detecting a link (DHCP, MDNS, etc.) I finally found what I was looking for: Broadcast packets, “HomePlug AV” protocol, “Atheros_something” MAC, “Action Required Notification (Bootloader)”. Awesome! This thing is even politely asking me to remote-boot it. Let’s figure out how.
Armed with the right keywords to feed to my preferred search engine, I finally found “open-plc-utils“. BSD-Licensed tools to set up Atheros-based PLC equipment. And, not really surprisingly, that includes a “plcboot” tool, which does just that – feed the PLC a firmware such that it can proceed to boot.” aka “
- Rename the .nvm and .pib files from the manufacturer firmware package to nvm and pib (The atheros utilities are picky when it comes to file names, something I only found out after head-scratchingly reading the code.)
git clone https://github.com/qca/open-plc-utils.git cd open-plc-utils make plc/plcboot -N nvm -P pib
- Finally, flash the firmware again, using the manufacturer tool. plcboot only performs a one-time boot when given the options above. To make the firmware permanent again, the flash needs to be rewritten. (Allegedly, plcboot can do that too, but it needs a “softloader” file, which I couldn’t be bothered to extract from the TP-Link software.)
I love the fact that chip manufacturers are building in sensible bootloaders, and that there is open source software available to access these. This is for example also the case with the Atmel ARM processor families of Arduino Due fame. I, for one, welcome this trend, making it increasingly hard to turn your hardware into a paperweight. On the downside, OEMs like TP-Link try to hide these as best as they can: the manual just says to return the device to the distributor for service when experiencing the symptoms I’ve encountered.
Bottom line: When a firmware update goes bad, don’t panic. It’s just a matter of finding the right tools. Also, it helps a lot having a general grasp of how things work on the inside to actually know what may or may not be possible.