I was poking around in ddb trying to figure out why wdc is upset and 
managed to cause this. More later, session cap is available since I'm 
working from serial console, and this is a Beige G3.

...
wdc0:0:0: lost interrupt
         type: ata tc_bcount: 65536 tc_skip: 0
wdc0:0:0: lost interrupt
         type: ata tc_bcount: 65536 tc_skip: 0
wdc0:0:0: lost interrupt
         type: ata tc_bcount: 65536 tc_skip: 0
wdc0:0:0: lost interrupt
         type: ata tc_bcount: 65536 tc_skip: 0
wdc0:0:0: lost interrupt
         type: ata tc_bcount: 65536 tc_skip: 0
Breakpoint at   netbsd:cpu_Debugger+0x10:       lwz     r0, r1, 0x14
db> bt
0x004b0ee0: at zs_abort+0x70
0x004b0ef0: at zstty_stint+0xd4
0x004b0f10: at zsc_intr_hard+0x124
0x004b0f30: at zshard+0x54
0x004b0f50: at ext_intr+0x104
0x004b0fa0: at trapstart+0x8f4
0xd5640d20: at Idle+0x24
0xd5640d30: at mi_switch+0x210
0xd5640d70: at ltsleep+0x478
0xd5640db0: at sys_select+0x1d4
0xd5640ed0: at syscall_plain+0xe0
0xd5640f40: user SC trap #93 by 0xefd234b8: srr1=0xf032
             r1=0xffffb1c0 cr=0x24000048 xer=0x20000000 ctr=0xefd234b0
db> sync
syncing disks... panic: kernel diagnostic assertion "emsr & PSL_EE" 
failed: file "/usr/src/sys/arch/macppc/macppc/extintr.c", line 802
Begin traceback...
0x004b0b20: at __assert+0x28
0x004b0b30: at do_pending_int+0x278
0x004b0b70: at spllower+0x50
0x004b0b90: at vfs_shutdown+0x44
0x004b0bb0: at cpu_reboot+0x1c0
0x004b0be0: at db_sync_cmd+0x20
0x004b0bf0: at db_command+0xc8
0x004b0ca0: at db_command_loop+0xf4
0x004b0db0: at db_trap+0x138
0x004b0dd0: at kdb_trap+0xd8
0x004b0e00: at ddb_trap_glue+0x78
0x004b0e10: at trapstart+0xd08
saved LR(0xfffffffd) is invalid.End traceback...
dumpsys: TBD
rebooting