Hi,
  I met a problem when I play with SIMH/VAX version 3.30 and
NetBSD/vax version 1.6.1. To generate the problem, do the following:
1. go to simh directory PDP11/
2. edit the file pdp11_rq.c, add "UNIT_DIS" to the flag of unit
rq_units[2], to disable unit 2, such that you have the following,

UNIT rq_unit[] = {
	{ UDATA (&rq_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE+
		(RD54_DTYPE << UNIT_V_DTYPE), RQ_SIZE (RD54)) },
	{ UDATA (&rq_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE+
		(RD54_DTYPE << UNIT_V_DTYPE), RQ_SIZE (RD54)) },
	{ UDATA (&rq_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE+UNIT_DIS+
		(RD54_DTYPE << UNIT_V_DTYPE), RQ_SIZE (RD54)) },
	{ UDATA (&rq_svc, UNIT_FIX+UNIT_ATTABLE+UNIT_DISABLE+UNIT_ROABLE+
		(RX50_DTYPE << UNIT_V_DTYPE), RQ_SIZE (RX50)) },
	{ UDATA (&rq_tmrsvc, UNIT_DIS, 0) },
	{ UDATA (&rq_quesvc, UNIT_DIS, 0) }  };

3.make executable, "make BIN/vax"
4.suppose you have installed NetBSD/vax to the RD53 file "netbsd.dsk",
and try to boot from that file mounted at rq3.

Now because there is a gap (rq2 is disabled), NetBSD/vax fails to boot
from rq3. See the screen message for details.

--vax, 9000

$ ./vax
 
VAX simulator V3.3-0
sim> load -r KA655.BIN
sim> set rq0 rd53
sim> at rq0 test.dsk
sim> set rq1 rd53
sim> at rq1 SCSItest.dsk
sim> set rq3 rd53
sim> at rq3 netbsd.dsk
sim> boot cpu
 
 
KA655-B V5.3, VMB 2.7
Performing normal system tests.
40..39..38..37..36..35..34..33..32..31..30..29..28..27..26..25..
24..23..22..21..20..19..18..17..16..15..14..13..12..11..10..09..
08..07..06..05..04..03..
Tests completed.
>>>show dev
UQSSP Disk Controller 0 (772150)
-DUA0 (RD53)
-DUA1 (RD53)
-DUA3 (RD53)
 
UQSSP Tape Controller 0 (774500)
-MUA0 (TK50)
-MUA1 (TK50)
-MUA2 (TK50)
-MUA3 (TK50)
 
RLV12 Controller 0 (774400)
-DLA0 (RL01)
-DLA1 (RL01)
-DLA2 (RL01)
-DLA3 (RL01)
 
Ethernet Adapter 0 (774440)
-XQA0 (08-00-2B-AA-BB-CC)
>>>boot DUA3
(BOOT/R5:0 DUA3
 
 
 
  2..
-DUA3
  1..0..
 
 
>> NetBSD/vax boot [1.11 Wed Sep 11 10:05:08 UTC 2002] <<
>> Press any key to abort autoboot 0
nfs_open: must mount first.
open netbsd.vax: Device not configured
> boot netbsd
1517664+210032 [153168+110527]=0x1e64f4
[ using 264228 bytes of netbsd ELF symbol table ]
Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002
    The NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 1982, 1986, 1989, 1991, 1993
    The Regents of the University of California.  All rights reserved.
                                                                       
NetBSD 1.6 (GENERIC) #0: Wed Sep 11 10:14:37 UTC 2002
    autobuild@tgm.daemon.org:/autobuild/vax/OBJ/autobuild/src/sys/arch/vax/compi
le/GENERIC
           
MicroVAX 3800/3900
cpu: KA655, CVAX microcode rev 6 Firmware rev 83
total memory = 16328 KB
avail memory = 11816 KB
using 229 buffers containing 916 KB of memory
mainbus0 (root)
ibus0 at mainbus0
uba0 at ibus0: Q22
dz1 at uba0 csr 160100 vec 304 ipl 15
mtc0 at uba0 csr 174500 vec 774 ipl 15
mscpbus0 at mtc0: version 5 model 3
mscpbus0: DMA burst size set to 4
mt0 at mscpbus0 drive 0: TK50
mt1 at mscpbus0 drive 1: TK50
mt2 at mscpbus0 drive 2: TK50
mt3 at mscpbus0 drive 3: TK50
uda0 at uba0 csr 172150 vec 770 ipl 15
mscpbus1 at uda0: version 3 model 3
mscpbus1: DMA burst size set to 4
ra0 at mscpbus1 drive 0: RD53
ra1 at mscpbus1 drive 1: RD53
qe0 at uba0 csr 174440 vec 764 ipl 15
qe0: delqa, hardware address 08:00:2b:aa:bb:cc
rlc0 at uba0 csr 174400 vec 160 ipl 15
rl0 at rlc0 drive 0: RL01, drive not loaded
rl1 at rlc0 drive 1: RL01, drive not loaded
rl2 at rlc0 drive 2: RL01, drive not loaded
rl3 at rlc0 drive 3: RL01, drive not loaded
Kernelized RAIDframe activated
ra0: size 138672 sectors
ra1: size 138672 sectors
boot device: <unknown>
root device: