Well I got on the bandwagon and bought 70 of these modules. I hope they all or mostly all work. Anyways, I have been poking through the ROM images posted, and I found a font inside of the parallel flash. It lives around 83180h or so (I will check for more than 1 copy of it... the install PDF claims there's backup firmware in the flash in one of the troubleshooting sections). The font looks like this:
I used yy-chr to grab it. Interesting that it's 6 pixels high, I guess this is so they can fit 6 lines of it on one of the modules.
Was poking through the EEPROM_panel file too, and it seems to be calibration data and possibly pixel order data too. There's several distinct sections of data. The EEPROM_control file is kind of weird, there's obviously data in here but it doesn't seem to be calibration data, I am not sure what would be living in here. I guess it could be a local copy of adjusted calibration data maybe?
My current working theory is on bootup, the controller will fetch the panel's calibration and control data out of the EEPROM_panel chip and load it into the SRAM (after some kind of processing and possible calibration with the light sensor/LEDs). I guess over time the panel could recalibrate itself too. The SRAM most likely holds the frame buffer as well, and during scanout it reads the pixel data and calibration data and does the fixup.
Reading literature for other similar LED walls, they do a 3*3 matrix multiply for every single pixel to effect the calibration. I am not sure if this does it, but I wouldn't be surprised if it does. It might be interesting to creatively corrupt the RAM contents as it runs to see if anything happens.
Because there is a font in the ROM, this thing most likely has some kind of diagnostics it can perform.