I have more information on the odd 0x29 traps on my LX.

I put an SBus cgsix card into the LX.  Pointing my code at the onboard
cgsix still dies the same way.  Pointing my code at the addon cgsix
works Just Fine.

I still have no idea what's really happening (I am inclined to suspect
hardware bugs in the path to the onboard cgsix), but at least I have a
workaround.

In case it matters to anyone, here are the boot lines for the addon:

cgsix0 at sbus0 slot 0 offset 0x0 level 9: SUNW,501-2325, 1152 x 900, rev 11

and the onboard:

cgsix1 at sbus0 slot 3 offset 0x0 level 9: SUNW,501-1672, 1152 x 900, rev 8

The SS20 I mentioned in my first message (the one which works) has a
board that's reported as "SUNW,501-2325" and "rev 11" as well.  Maybe
it's a bug in rev 8 or something.

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