I came across this page while looking for man pages to SYSVr3 for someone... Completely unrelated but I thought it’d be interesting to someone. Apparently it can be built with GCC/GAS/Binutils from a 680x0 based SUN.

From the readme:

Xinu for the ATT7300 (3B1) and MECB (Motorola Educational Computer Board)

This is an implementation of the Vol. I Xinu for diskless singleboard 68000/68010 systems. The ATT7300 is the preferred system, having at least .5M memory vs. the MECB's cramped 32K.

ATT7300 hardware and the Xinu support provided here:

MC68010, 10Mhz

.5M-2M onboard memory, up to 4M with expansion memory

VA space of 4M, monolithic page table (not used here for paging)

RS232 port with software-selectable baudrates to 19.2K baud, with NEC7201 SLU (used for Xinu console)

Line clock interrupting at 60Hz, used for Xinu clock.

Keyboard interface with MC6850 SLU--Xinu tty driver for it here, but not compatible with the serial encoding from the native keyboard, so you need to attach another terminal to use it.

Centronics parallel printer port (start on LPR driver here, fleshing it out is a good student project)

Floppy disk--not supported in Xinu, but used to boot monitor/downloading system

Hard disk--not supported or needed.

Realtime clock--not supported in Xinu.

Telephone interfaces--not supported.

Bitmap graphics monitor interface--not supported.

MECB hardware and Xinu support:

MC68000 CPU, 4Mhz

32K memory

2 serial ports, each with MC6850 SLUs, available as Xinu ttys or dlcs. Easy to add a third MC6850 at 0x30001, for 2nd dlc. (However running a Xinu net takes more than 32K memory, not so easy)

MC68230 PI/timer: Timer used as Xinu clock, setup for LPR driver using PI.