power failure interrupt on Netra X1

[Chris Ross <cross+netbsd%distal.com@localhost>]

  I have NetBSD 5.1 (or, 5-stable from some many months ago) running on a Netra 
X1.   This seems to be working just fine.  The network interfaces seem unduly 
slow, but it is old hardware, so I don't presume that's a NetBSD issue.

  This weekend I tried net-booting a sparc64 FreeBSD 9-stable, just to see how 
it fared on the same hardware.  But, it never got to multiuser.  I'm not sure 
it got to single-user.  During boot, the end of the dmesg was:

uart1: <16550 or compatible> at port 0x2e8-0x2ef irq 43 on isa0
ctl: CAM Target Layer loaded
Timecounter "tick" frequency 500000000 Hz quality 1000
Event timer "tick" frequency 500000000 Hz quality 1000
Timecounters tick every 1.000 msec
Power Failure Detected: Shutting down NOW.

  After which, even a serial break, which would normally drop back to the OBP, 
had no effect.  It was dead until I used the LOM to reboot it.

  The FreeBSD list members suggested:

> This means that the machine is generating a power failure interrupt,
> which causes FreeBSD to initiate a graceful shutdown rather than
> waiting for the power to supply to suddenly die, which could cause
> data loss.
> In general, it's very model specific whether Sun hooked up that
> interrupt to anything and to what. F.e., in U5/U10 it's just
> connected to the power button rather than a circuit that monitors
> the power supply. I don't know for certain what it is connected to
> in X1. However, given that these latter use an ACPI-style power
> button and were intended as servers, it's quite likely that their
> power failure interrupt actually is connected to a power supply
> monitoring circuit.

  So there's the open question as to whether there is a real problem that's 
causing this interrupt, but my question to this list is what NetBSD is doing 
such that this appears to not cause any sort of problem?  Do we have special 
code in the interrupt handler to cope with this?  I actually have a 
recollection of such, from years ago, perhaps with this same machine.  And I 
intend to "use the source, Luke" to check on that.  But thought I'd send a note 
out to the list to see if others recall any better than I do.

  Thanks.

                                 - Chris