This is in a 7500 with an Adaptec 2940UW PCI card, (driver version 4.1).  I
can load almost any kernel from floppy or a SCSI drive on another bus (MESH
"internal" or NCR "external").  Once it gets to the point of probing the
SCSI busses for devices, it always fails in pretty much the same way:

[...]
ahc0 at pci0 dev 15 function 0
ahc0: interrupting at irq 25
ahc0: aic7880 Wide Channel A, SCSI ID=7, 16/255 SCBs
scsibus0 at ahc0 channel 0: 16 targets, 8 lunx per target
[...]
Waiting 2 seconds for scsi devices to settle
ahc0: ahc_intr = referenced scb not valid during SELTO scb(9, 255)
[repeats a lot]
probe(ahc0:0:0): SCB 1d - timed out while idle, SEQADDR == 0x5
SCSIRATE == 0x0
probe(ahc0:0:0): SCB 1d: Immediate reset.  Flags = 0x4040
probe(ahc0:0:0): no longer in timeout, state = 0
panic: Waiting List inconsistency.  SCB index == 255, yet numscbs == 30.
stopped at cpu_Debugger+0x10:    lwz r0, r1, 0x14,
db> trace
at wskbd_cnbell+190
at wskbd_cnbell+1348
at wskbd_input+68
at kbd_intr+bc
at kbd_adbcomplete+c0
at kbd_adbcomplete+5c
at adb_soft_intr+d0
at softclock+208
at hardclock+23c
at decr_intr+118
at extint+call+180
at cpu_switch+30
at mi_switch+1a0
at ltsleep+294
at scsipi_execute_xs+f8
at scsi_scsipi_cmd+190
at scsipi_command+bc
at scsipi_inquire+7c
at scsi_probedev+d0
at scsi_probe_bus+108
at scsibus_config_interrupts+64
at config_interrupts+16c
at configure+78
at main+41c
at __start+90

The kernels I tried are:
<ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-1.5_ALPHA2/macppc/binary/sets/kern.tgz>
<ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-1.5_ALPHA2/macppc/installation/floppy/bo
ot.fs>
<ftp://ftp.netbsd.org/pub/NetBSD/arch/macppc/snapshot/20000620-1.5/binary/kernel
/netbsd.GENERIC.gz>
<ftp://ftp.netbsd.org/pub/NetBSD/arch/macppc/snapshot/20000620-1.5/installation/
netbsd.ram.gz>
<ftp://nandra.iri.co.jp/pub/NetBSD/macppc/netbsd.hfsboot>

The firmware driver for the Adaptec card is from:
<http://www.adaptec.com/support/overview/pd2940uw.html#drivers>
One interesting note is that they have different drivers for "AV PowerMacs"
and everything else (where the "AV PowerMacs" are the 7200-9600").

Any suggestions, other than unplugging the Adaptec PCI card?

Thanks,
  -- MW