It is hard to consider anything ported when interrupts and DMA remain out of reach. This article describes only the trivial parts of porting.

It would have been better to get those working and then publish.

Also, sorting display objects when rendering seems pointless considering the small number of objects that could possibly be on there. If there are layers it would be better to keep them on separate lists. (It was not clear which direction is "y". Is that toward top of screen, or bottom, or does it mean a layer?)

That said, I will always upvote microcontroller project reports, and will look forward to the rest.