Video of First Blinking Pixel!
Last night, the first pixel finally turned on. We have two videos, one of two-color transitions and one of purely random colors. Check these out. Then imagine another 511 pixels next to it, lighting up the room in trippy color.
The problem was due to an incorrectly inserted programming cable. When inserted backwards, the AVR programmer would still turn on, and report that everything was ok. When trying to program a chip, however, there were plenty of errors. It just so happens that the AVR 6-pin ISP connection delivers power to a programmer when inserted backwards, by drawing power from the RESET and MISO lines. With a working programmer, we could finally put the firmware on the main chips, and set them to the proper speed, 8 Mhz. Then... it worked.
Things are looking up now, with the most critical (and delayed) piece in place!