In the process of bringing up Palawan DVT1, I've run across a number of bugs in Grainuum. Most notably, several subtle timing errors where the loop was one cycle too short or too long. Or in the case of the end-of-packet signal, four cycles too short.
There was also an issue with a failure to unstuff everything after the first stuffed bit. That is, if you sent over 0xffffffff, you'd see something like 0xff7ffdf on the embedded host.
These problems have been fixed, and I've managed to send several hundred megabytes of data back and forth across a USB HID link without a single error.
Now that there is a reliable link, it's time to move on to writing the updater, and creating the actual Palawan firmware base.