DMX light not responding on GalliumOS Chromebook

[superlou]

I've been using dmx-rs as the DMX interface for a basic DMX controller. It's been working great with a cheap USB<->RS-485 dongle on my Linux Mint desktop. With the exact same lighting hardware but running on an Acer C720 GalliumOS Chromebook, the DMX light doesn't react to commands. It has a blinking LED indicating it's getting some kind of traffic, and the dongle is lit up indicating I have control of the serial port.

I don't think this is explicitly a dmx-rs issue, but I figured I'd ask with the hope that someone might have an idea on how to debug this. My fear is that I have some kind of subtle timing issue that is only debuggable via oscilloscope.