Re: New pmap module for m68k

[Jason Thorpe <thorpej%me.com@localhost>]

> On Oct 25, 2026, at 7:55 AM, Romain Dolbeau <romain%dolbeau.org@localhost> wrote:
> 
> As far as I can tell, only U0 (bits 8 in the page descriptor, visible
> to pin UPA0) is used by the NetBSD kernel (for PG_W), while the first
> available UR bit from the '040 (bits 11, not outputed to external
> hardware) is not used. If PG_W was moved from bit 8 to bit 11, the UPA
> bits would be freed for the SMP-intended purpose of snooping (with
> Motorola suggesting wiring SC0/1 to UPA0/1).

The U0 bit is only used in the older Utah/Hibler pmap_motorola.c, largely because it was original written to support the HP MMU (used in the HP 9000/320 and 350) and the 68851, and 68040 support was shoe-horned in there and the bit was never moved elsewhere.

-- thorpej