I'm both ashamed of myself for having gotten into this mess in the first place, but also proud of myself for figuring out how to fix it on my own. So I figured I'd share on here in case someone else runs into the same issue.
On the AR750 I attempted to flash the firmware meant for the AR300M. I had just set up the AR300M the day before and, in a lapse in judgment, didn't think the two devices would have separate firmware install files. The result was a device in a continuous boot loop. After fiddling around with Wireshark I discovered that the AR750 will, when attempting to recover from an upgrade failure, attempt to download a bin file from a TFTP server.
The AR750 will assign one of the interfaces (I believe the "WAN" interface on the left) an IP of 192.168.1.1. It then sends out an ARP request for 192.168.1.2. If it gets a response from the .2 machine, the AR750 will ping it. If the ping is successful, it will then attempt to download the file "openwrt-gl-ar750.bin".
The rest is pretty easy to guess if you've installed AREDN firmware before. Get a TFTP server program like Serva on Windows, or use dnsmasq if you're on Linux, rename the *correct* AREDN firmware file to "openwrt-gl-ar750.bin", put it in the TFTP folder, and let the machines do the rest.
On the AR750 I attempted to flash the firmware meant for the AR300M. I had just set up the AR300M the day before and, in a lapse in judgment, didn't think the two devices would have separate firmware install files. The result was a device in a continuous boot loop. After fiddling around with Wireshark I discovered that the AR750 will, when attempting to recover from an upgrade failure, attempt to download a bin file from a TFTP server.
The AR750 will assign one of the interfaces (I believe the "WAN" interface on the left) an IP of 192.168.1.1. It then sends out an ARP request for 192.168.1.2. If it gets a response from the .2 machine, the AR750 will ping it. If the ping is successful, it will then attempt to download the file "openwrt-gl-ar750.bin".
The rest is pretty easy to guess if you've installed AREDN firmware before. Get a TFTP server program like Serva on Windows, or use dnsmasq if you're on Linux, rename the *correct* AREDN firmware file to "openwrt-gl-ar750.bin", put it in the TFTP folder, and let the machines do the rest.