Subject: Re: 240/260 CPU hacking....
To: None <port-pmax@netbsd.org>
From: Bob Lantz <lantz@Stanford.EDU>
List: port-pmax
Date: 03/27/2001 18:56:23
On Tue, 27 Mar 2001, John Maier wrote:

> > IRIX eventually evolved into a stable 64bit OS which runs 32bit
> > applications, then NetBSD could do.
> 
> Sure, the R4x00, even in 64bit mode can run 32bit MIPS II code.  The
> problem is, if the R4x00 is initalized in 32bit mode (via a small serial
> PROM) it can't use it's 64bit MIPS III instuctions efectively.  i.e. running
> 64bit instructions and data on a 32bit bus requires two words per
> instruction.

Why should this be? The instruction length is still 32 bits. 

> This would be the biggest stumbling block in getting a NetBSD 64bit running
> on a /260.
> Well not stubling block but it would run slow (half as fast as 32bit
> instuctions).