A flurry of activity over the last few days has brought us to the end of the road with this project. Marlin 2.0 now has support for the chitu boards in bugfix-2.0.x, and I opened a PR that will enable disk based updates that should be done soon. THe disk based updates required a bit more reverse engineering, because the bootloader leaves hardware in a half-initialized state. Since DMA drops receive buffers straight at the beginning of RAM, I had to write some custom initialization code to turn off interrupts, clear devices and reset the system. Soon, building Marlin will be as simple as "pio run -e chitu_f103" and copying over the update.cbd to an SD card.

It's been fun...