The continuing saga of my 5000/200 [was Re: DECstation 5000/200 timekeeping]

So, about that 5000/200 that's been suffering from inability to keen
even vaguely decent time: the saga continues.

Lacking much else to try, I decided to try for 1.4T on the 5000/200, in
the hope that that would work better.

1.4T appears to have a moderately mature pmax port, but it has next to
no cross-build support, so it's a bit more complicated.  I installed
stock 1.4 and timekeeping is _much_ improved - but now, the SCSI driver
is flaky.  It's not using the MI SCSI subsystem; disks show up as, for
example,

asc0 at tc0 slot 5 offset 0x0 (bus speed: 25 MHz) : target 7
Beginning old-style SCSI device autoconfiguration
rz1 at asc0 drive 1 slave 0 SEAGATE ST373307LC rev 0003
rz1: 69809MB, 49855 cyl, 4 head, 204 sec, 512 bytes/sect x 142969680 sectors

and, unless the hardware decided to break just at the same time as I
started running 1.4T, this rz stuff is depressingly flaky.  I see
things like

rz1: Illegal request

which typically gets reflected as EIO to userland.  Sometimes there are
additional messages as well, such as

asc_get_status: cmdreg 11, fifo cnt 3

I've got the machine running pseudo-diskless (booted off a disk, but
NFS-mounted my house NFS server and chrooted to that mount point) to
sidestep the SCSI issues and am trying a build of 1.4T into /altroot,
in the hope that that will produce something more useful.  If not, I
may experiment with other versions; I've got an archive of, I _think_,
every release from 1.0 through 6.1.2, though it remains to me seen
whether there's a version that doesn't suffer from either of the above
issues (flaky SCSI or flaky timekeeping), and any version other than
1.4T, 4.0.1, or 5.2 would mean a significant effort to port the most
important of my changes over.

I also may have a stab at moving it to the MI SCSI subsystem, if 1.4T
doesn't bring that in.

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