Filesystem Information While searching through the partial filesystem I extracted from the package updates, I found /etc/dev.tar which appears to be a skeleton of the dev filesystem. We can infer several things about the partition layout on the internal MMC with this information.
Building the SD Card Partitioning the SD Card It appears that uBoot will only attempt to use the partition named main-A as the root filesystem. I created a small partition named _ because there is a bug with get_partition_num that will cause it to occasionally be unable to find the first partition on the disk.
... Update: You can view Ike Clinton’s paper that is mentioned in this article here. It is the basis for most of this research so far. There is also a Slack channel and wiki about this subject. The PCBs I ordered came in but I haven’t had time to solder the components on or test it out. A few people in the Slack channel have gotten their own code running on the Echo, so it is possible!