Re: CVS commit: src/sys/arch/x68k/stand/boot_ustar

[Dennis Ferguson <dennis.c.ferguson%gmail.com@localhost>]

On 15 Apr, 2014, at 05:14 , Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost> 
wrote:
> - NetBSD/x68k supports only X680x0 machines with MC68030 and higher
>  processors.
> 
> - Normal X68000 machines (i.e. all X680x0 except X68030) have MC68000,
>  so 030 accelerators are required for the X68000 models, i.e.
>  XVI, SUPER, EXPERT, PRO, and ACE.
> 
>  (BTW the normal X68030 has MC68EC030 so users also have to replace
>   its CPU to with MC68030 to use NetBSD/x68k)
> 
> - On the other hand, probably early x68k developers considered
>  that some stupid users could try to boot NetBSD/x68k on X68000
>  without 030 and bootloaders should have some sanity checks.

I'm pretty sure NetBSD could never run on a 68000 since the 68000
had no memory management unit.  The 68010 and 68020 didn't have memory
management units either, but Sun did proprietary MMUs for both (that's
sun2 and sun3, respectively) and I think other companies may have done
MMUs for the 68020.  The 68030 was the first CPU in the series to come
with an MMU built in.

That generic x68x requires a 68030 makes sense since that's the first
CPU where the code can count on knowing how the MMU works.  A 68020
would have a manufacturer-specific MMU, while for the 68010 there is
only sun2.  There is no reason to restrict the instruction set to
that of the 68000 in any case since NetBSD won't run on that.

I once had a 68000 board that ran a 4.3 BSD kernel, but it was a
4.3 BSD kernel with all the process scheduling hacked out so that
it ran exactly 1 compiled-in "user space" process, without memory
protection.  I used it as an ntp server.

Dennis Ferguson