Sun 3x <==> Sun 3 compatibility

[Allan Doyle]

Scenario:

	We have a Sun-3/280 based system at a customer site.
	We want to install a second system at the site.
	In order to give the customer a performance bonus, we 
	  want to upgrade to a 3-3/480.
	Our customer has spares for the 3/280 and does not want
	  to pay for a spare 3/480 CPU.

	We say "No problem, use the 280 spare as a fallback and
	the second system will run, albeit a little slower."

Problem:
	When I plug a 280 CPU into the system from which I have
	pulled the 480 CPU, it does not boot. I have, of course, already
	copied a kernel built on a 280 system into the root partition.
	The boot program gives up right away because of a page mapping
	problem.

Obviously, I'm getting bitten by boot code that was configured for a 68030
with native MMU, or am I? What is going wrong here? How do I fix it?  Once
I get the sucker to boot, what else is going to bite me. I noticed a bunch
of symbolic links in /usr/shar/mdec that are CPU specific.

The real question is: How do I put the 280 CPU into the system with the
shortest turnaround? The path of doing a new installation of 4.0.3 each
time I swap CPUs will probably work but takes too long. (The client after
all, likes short repair times...).

Any ideas you folks have will be welcome. I will post a summary and if I
get a good procedure, I'll post that as well.

	Allan Doyle


Allan Doyle                                              adoyle at bbn.com
BBN Systems and Technologies Corporation		 (617) 873-3398
70 Fawcett Street,   Cambridge, MA 02138