Boot-time question

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

I don't know if anyone remembers enough of old booters/kernels to help
with this, or perhaps if this is version-independent....

Teal deer version: trying to boot NetBSD/i386, machine consistently
hard-resets at some point after loading kernel and before kernel prints
anything, I'm wondering if anyone has hints for how I might be able to
get some handle on debugging it.

Longer version....

A friend recently gave me two tablets.  Their model numbers are DT360
and DT366.  They have proved to be basically peecees.

They came to me with Windows CE installed on the DT360 and Linux on the
DT366.  In case it helps, uname -a on the Linux install says

Linux dt366 2.6.26-1-486 #1 Sat Jan 10 17:46:23 UTC 2009 i586 GNU/Linux

Naturally, I wanted to put NetBSD on them.  So I used F1 on a keyboard
to drop into the BIOS, tell it to boot from USB disk first, and put my
NetBSD/i386 USB drive on them.

On the DT360, this worked fine.  It booted just fine and I installed
NetBSD on its internal flash "disk".  (It was a bit cramped - half a
gig - but I made it fit by dropping source code.)

On the DT366, I have been unable to make it do anything but hard-reset
immediately after loading the kernel.  The booter starts and runs
apparently normally, including user interaction.  Telling it to boot,
though, produces the usual twirler, the %d+%d+%d [%d+%d+%d text, then a
little more text I get only the briefest of glimpses of (I think it
includes a hex number), and then it resets.  In my experience, this
usually means I'm trying to boot an amd64 disk on an i386 machine - but
this same disk boots fine into NetBSD/i386 on the DT360.

This is with a 4.0.1 kernel; I tried a 1.4T i386 kernel as well, with
the same results (well, the numbers were different, but it still resets
in much the same way).

I'm wondering if anyone has any hints on how I might be able to start
debugging this.  It's particularly frustrating because, as far as I can
tell, it resets before it even enters the loaded kernel - certainly
before it prints enough text for me to see, though UTSLing indicates
the kernel does quite a bit of stuff before it prints anything.

I'm going to be experimenting a bit more - for example, I tried the
1.4T kernel with the 4.0.1 booter; I don't know if that might be
relevant.  Oddly, the booter reports itself as being the i386 booter in
one place and the amd64 booter in another, even though it boots fine on
the DT360, which I have no reason to think is any more amd64 than the
DT366 (also works on various other i386-but-not-amd64 machines):

USB Boot Device : MASS Storage Class [0400h/51h/3Fh]
NetBSD MBR boot

NetBSD/i386 ffsv1 Primary Bootstra


>> NetBSD/amd64 BIOS Boot, Revision 3.3
>> (mouse%Basckstop.Rodents-Montreal.ORG@localhost, Mon Jul 27 14:31:13 EDT 2015)
>> Memory: 639/252608 k
Press return to boot now, any other key for boot menu

I manually transcribed the BIOS's self-report screen; it says

Rev: XpressROM_BIOS_DT366_0.01.18                 Built: 07/01/2005 17:29:43
GX2 Rev: 2.1 @ 398MHz            PCI: 33MHz                5535 Rev: A3
Memory: 253632k @ 199MHz/DDR   CAS: 2.5   FbDIV: 9/24 CPUDIV: 0/2 GLDIV: 2/4
Floppy A: 1.44M  Drive 80: 524MB   COM1: 03F8              XpressROM: 4.23.00
RTC: Present     Drive 81: 2675MB                          VSA: 03A0
USB: Legacy                                                VideoBIOS: 051F
PM: Disabled
CPU Temp: 0°C

I'm going to see if I can figure out what's with the amd64 claim and
see if (if I can) replacing it with the i386 one makes any difference.
And, of course, see if I can cokme up with any way to debug this.  But
if anyone has any suggestions that might help, I'd love to hear.  I
can, of course, rebuild things with special-purpose code added, if that
might be useful - but I'm at something of a loss to figure out what
code ot add, or where, to do anything helpful.

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