I have been trying to boot netbsd onto an XL266.  Many have offered
suggestions and sent things to try.  If I only wanted unix I would
have settled on Linux, since it is known to run with the ARC console;
however, I was ultimately targeting Digital unix because I need to
use the PL/I compiler (which I wrote, with help from colleagues).

I thought I would summarize my experience so that anyone else trying
the same thing wouldn't have to duplicate my experiments.

The XL233/266 machines were designed (probably by marketing) to be NT
only machines, because they were aggessively priced.  Hence, the
flash ROM is only 512KB, big enough to hold the ARC console, but not
also SRM, the latter which is required to boot anything other than
NT.

The boot sequence on these platforms is as follows:

	SROM  ->  DROM  ->  ARC

on the cpu daughterboard are jumpers to prevent the transition from
SROM to DROM (used for manufacturing) and , more importantly, a
jumper to cause the DROM code to load from the failsafe floppy rather
than the ARC console from flash.  Thus, if you trashed your flash,
and had the the right floppy, you could still bring up NT from the
ARC on the floppy.

I'm not sure of the exact function of the first two stages, because
there is not a lot of documentation available.  I have scoured
Digitals ftp site, and nada.

I have tried several different firmware images, one of them modified
by Drew at Duke with the mkboot utulity, I have tried using the ARC
update utility, I have tried "RUN A PROGRAM" option under the ARC menu
and they all failed.  This last one failed, I believe, because of an
object code format incompatibility (i.e. header infor, magic number
or the like).  Now to run programs from ARC, it has to be in FAT
format, and you have to give the full path, thus

scsi(0)disk(0)rdisk(0)partition(1)\XLUPDATE.EXE  for drive C
multi(0)disk(0)fdisk(0)\XLUPDATE.EXE

according to documentation on the ftp site the name has to be as
above for ARC to recognize it, and it has to be FAT

The images I was trying were based on SRM console, the theory being
that like linux milo you start life FAT and then slim down.

CONCLUSIONS:

I have a hunch that the hooks between DROM and ARC are probably the
same as SRM, and I bet that there exists within Digital a failsafe
floppy image of SRM for this platform.  I was operating under the
theory that I could build a floppy image, in lieu of the flash, which
would always be used to boot unix (from SRM).  For the moment, linux
is the only option, Digital unix and netbsd are out.

For anybody who is interested I have more details.