Re: Considering EOL of HP320/330/350 (Re: NetBSD/virt68k booting multi-user)

> On Jan 6, 2024, at 8:07=E2=80=AFPM, Izumi Tsutsui =
<[email protected]> wrote:
>=20
> thorpej@ wrote on port-m68k:
> https://mail-index.netbsd.org/port-m68k/2024/01/06/msg000845.html
>=20
>>> I guess we can simply change PGSHIFT to 13, but I wonder we should
>>> also consider again to reorganize 040 pmap to make it possible to
>>> expand L2 STEs on demend, as mhitch@ mentioned back in 2009:
>>> https://mail-index.netbsd.org/port-m68k/2009/05/12/msg000143.html
>>>=20
>>> Maybe we also have to consider about 3-level pmap like sun3x..
>>> https://mail-index.netbsd.org/port-m68k/2001/07/20/0003.html
>>=20
>> That's an idea, but that won't work for the HP MMU on the 320 / 350.
>=20
> I should have asked this earlier, but now is the good timing:
> "I'm considering dropping support of (at least) HP320 and =
HP318/319/330"

Boo :-(  I mean, I regret getting rid of my (pretty stacked) 9000/380 =
many years ago, but there was a time I had easy access to 319, 320, and =
350 models, although, alas, I did not own them.

> The reason why is it looks memory bus design of these hardware
> don't support CAS instruction.

I need to go back and re-read the signal description in the 68020 =
manual, I guess.  But, yah, the r/m/w instructions do assert a =
=E2=80=9Clock=E2=80=9D signal, I think.

> Recently (back in 2022) I have acquired HP319 and HP320
> (as hp300 maintainer) and tried NetBSD 9.3.
> However both machine panicked by bus error on CAS instructions
> in mutex_enter(9) during early boot:

[ ROOTROM Rev. C boot message elided=E2=80=A6 ]

> NetBSD/hp300 5.0 also fails in mutex_enter(9).
> NetBSD/hp300 4.0.1 boots:
> https://dmesgd.nycbug.org/index.cgi?do=3Dview&id=3D6786
>=20
> (The late) ryo@ commented that he also saw the similar bus errors
> on CAS/TAS instructions on his X68000 with 3rd party expansion RAM
> that didn't support read-modified-write cycle.
>=20
> I'm afraid HP320 and HP330 (also 318/319) have the similar hardware
> design, because SMP was unlikely yet in 1980s.
> (though it looks Sun 3/60 bus supports CAS properly)

Yah, it=E2=80=99s certainly possible that none of the 68020 HPs support =
it.  318 and 319 were basically 320s, and the 350 was, IIRC, a 320 + an =
external cache.  330 had the PMMU, so maybe it worked differently?

> I tried to build a kernel without CAS but using RAS for sun2/m68010
> implementation, it booted to multiuser on HP320:
> https://twitter.com/tsutsuii/status/1597909609205104640

I think we should do some indirection there to support those models =
using RAS.  Perhaps I=E2=80=99m just nostalgic (or a luddite :-), but I =
think so long as the burden isn=E2=80=99t too great, we should try to =
keep these machines running.

> (BTW, it looks HP98543 topcat seems to have VRAM only at even =
addresses
> so we need more work in rasops(9) (as 4-depth in 16-bpp?) to support
> it properly)

Perhaps we could bribe macallan :-)

> If the only reason we cannot switch to 3-level MMU pmap is HP-MMU,
> those machines (at least HP320) need more special work, including
> userland binaries, to keep them "supported".  That's my point.

Eh, I don=E2=80=99t see it as a huge burden.  I don=E2=80=99t see a real =
tangible benefit to switching the =E2=80=98851/=E2=80=98030 over to a =
3-level scheme just to match the 68040.  The pmap design I=E2=80=99m =
working with keeps the page tables in an rb-tree (and eliminates the =
fixed-size =E2=80=9Cuser PT map=E2=80=9D that linearly maps the user =
PTEs), and deals with =E2=80=9Cleaf=E2=80=9D as part of the lookup key.  =
Whether that is a 2nd or 3rd level table is irrelevant unless the leaf =
table doesn=E2=80=99t exist at which point the code paths diverge to =
deal with page table allocation.  And it handles 8K and 4K pages the =
same (just sizes the objects in the pools the PTs are allocated from =
differently).

> I wonder if HP350 (that has RAMs on its local bus, not 16-bit DIO =
bus?)
> supports CAS/TAS instructions (i.e. read-modified-write cycle), but
> I have not have a chance to acquireq it.
>=20
> Does anyone still have HP350 and tried recent NetBSD (5.0 and later)
> on it?
>=20
> Thanks,
> ---
> Izumi Tsutsui

-- thorpej