> Last time I looked into this, it looked pretty difficult. The Ultras
> are pretty radically different from the old Sparcs; they have the
> 64-bit address space, 

You can run the processor in 32-bit mode, this is how the first
Linux/Ultra port was done.  Little changes to the Linux/SPARC tree and
they got it up in under a month.  

The current Linux/Ultra is a 64-bit port, and it has most of the arch/
stuff completely redone (but it still uses the device drivers from the
SPARC port). 

> a different processor memory model (PSO, I
> think),

This really does not matter, except in a place or two.  You can program

> a fourth distinct MMU, a new memory bus architecture, and different 
> devices. 

Probably the frame buffer is the only new driver you will need (and
then, some Ultras come with cg6 and cg3 video cards, we are using the
same video drivers for the Linux/Ultra port).

The ethernet card is the HME, which is available on the 4m machines as
well, and then, they still use SBus, so most of your SBus code can be
used here with just minor adaptations.

Miguel.
-- 
miguel@roxanne.nuclecu.unam.mx     
The GNU Midnight Commander: http://mc.blackdown.org/mc
Linux/SPARC project:        http://www.geog.ubc.ca/sparclinux.html