I have been tinkering with AREDN as of late when I saw that they supported some of the GL.inet line of devices, which I enjoy as they are cheap, fairly well engineered, designed on top of OpenWRT. I am, unfortunately, 10 miles away from the nearest node and I think tunneling is "cheating" so I am slowly bootstrapping myself into a "local mesh" to experiement. I saw from forum posts that the Mikrotik hAP AC series of devices were a popular device to use and seemlingly recommended as the best "home node" so I recently purchased a hAP AC Lite (RB952Ui) off of Amazon.
Taking it out of the box and starting to read the flashing guidelines I realized I was spoiled by GL.iNet's embrace of OpenWRT where the flashing process was "upload firmware, press flash, wait, done". Nonetheless, I am good on TFTP, netbooting, and such. What gives me heartburn is warnings in the AREDN Instructions that say...
OpenWRT firmware (and therefore AREDN®) may experience a boot loop during installation of the sysupgrade file on Mikrotik devices with RouterOS v6.45.8 or newer.
...and a big warning on the OpenWRT Page that states...
OpenWrt is not compatible with the bootloader of RouterOS v7 or v6.46 or above. Do NOT upgrade the firmware on your device past RouterOS v6.45.8 or, if you did, downgrade to RouterOS Firmware v6.45.8 or earlier before installing OpenWrt.
...especially when my system is running RouterOS 6.48.6.
Thankfully, OpenWRT does have a pretty good explainer on how to downgrade the system and I downloaded the right files, uploaded them to the system, and merrily typed the requisite commands into the terminal. All was well, until I told the bootloader to downgrade...
Do you really want to upgrade firmware? [y/n] y
ERROR: can not change firmware to this version, please try newer one
Oh poop.
After having a minor panic attack thinking I wasted $60 on a device that now was useless to me, I cracked my knuckles and started researching the error message. Sadly, most references to it were buried in extremely long OpenWRT forum threads that never had a clear answer. I finally did find a reference that said "yeah, I put OpenWRT on a system that ran v6.48.6." but with no clarification on how many goats to sacrafice, the models of the ceremonial knives used, or what techniques used. Undaunted, I opted to take my chances that I was going to be one of the lucky ones in that "may" statement from AREDN.
I opted to take a more scenic route and decided to take my device and flash "vanilla" OpenWRT as a first step. This, I rationalized, would give me a better chance of having a successful flash from RouterOS to a non MikroTik operating system. I used the OpenWRT Instructions and TinyPXE to push the initial firmware image and then used the sysupgrade image to flash the bootloader. It took (what I felt was) a lot longer than what I was used to flashing the GL.iNet devices and I exhaled when the USR light went solid and I was able to see the familiar LuCi control panel. After cold booting it a few times to make sure the firmware image had "stuck" and that I wasn't accidentally booting off of a image in RAM somewhere, I logged into LuCi and flashed it with the AREDN firmware. Again, after waiting what seemed to be a long time, it did flash successfully and I am in busiess on my hAP AC Lite.
One thing that I did notice is that the device did seem to lock up about five minutes after its first boot into AREDN. I didn't do any kind of extended troubleshooting into it while it was in that state as I just groaned, thought I messed it up, and just power cycled it. It has been behaving since.
So, I can state that with RouterOS Firmware v6.46.8, you successfully reflash it with AREDN on a RB952Ui. Was I lucky? Maybe. But I wanted to post this out here to try to give a more definitive answer for other users who may be having the same heartburn I did while reading those incredbily long OpenWRT threads.