sun4_40 is now happy enough with my latest pull request that you can initialize the IDPROM, though apparently the SCSI and DMA support isn't solid enough to boot off a SCSI device.
First, booting up sun4_40 with -keyboard sparckbd will give you, by default, a SPARCstation IPC with 16 megs of RAM installed, and a bad IDPROM checksum:
You should press the N key on your keyboard to enter the Forth monitor. We can now update the IDPROM using instructions found here: https://groups.google.com/forum/#!topic/comp.sys.sun.admin/3eVsqoD8jVQ
byte 0: always 01
byte 1: first byte of host ID, machine ID (0x52, SPARCstation IPC)
bytes 2-7: MAC address, always starts with 08:00:20
bytes 8-b: Manufacture date, in my case 20160722
bytes c-e: Remaining three bytes of host ID
byte f: checksum (XOR of bytes 0-e)
After you do this, and make sure to type everything correctly, you can type "reset" to reboot the machine. At this point, you will see that it doesn't complain about the IDPROM checksum anymore.
Here's a crash course on Forth, followed by an interesting little Forth trinket.
It's a Mandelbrot generator! Courtesy of Lord_Nightmare for knowing the Forth snippet.