It's all open sauce.

A little birdie told me this only builds properly on Linux hosts ('buntu 13.10 confirmed OK); building with the target OMAP3430_RX51 produces a binary you can combine with GenericBooter which passes... stuff along from the boot environment (u-boot) to the xnu kernel.

The little birdie also told me that a real N900 on-hand (this was ported first to the N900 QEMU...) would help - you may want to send the guy one to help 'em along!

Birdie also notes that the recommended userland filesystem package for this would be iPhone OS 4.3.5. Accelerated graphics don't work for now, so you're stuck in console (non-single user at least!) mode.

This would also be semi-effortlessly portable to the N9/50 if a u-boot port was made. The N900 port is a good place to start.

Hardware keyboard doesn't work. Yet, at least. Use the serial console if you need it.