It seems that even in 1.5 the Pyxis DMA workaround is not perfect yet.
I was careful to try the netbsd.ram kernel, and it did not work properly
with my IDE disk. It was apparently able to read the disklabel but no
more than that. I did a careful "mount -r /dev/wd0d /mnt". At first it
just thought the superblock was invalid, on later attempts it crashed.
These are the same symptoms as when the workaround was first introduced.

If I make a kernel that just does not do IDE DMA, things work normally
(as far as I tested, anyway - read only).  I already use such a modified
kernel now with 1.4.1.

This is the remains of the console messages, as picked up after
subsequent reboot. First there are the messages from netbsd.ram, then
the crash message, then my normal 1.4.1 boot messages.  I have a
Personal Workstation 433au with an added ne2000 clone ne0, a SCSI
cd-writer cd1, and an IBM DPTA-353750 IDE disk wd0 .

Note that the output from the "trace" command is empty, so no stack 
backtrace.

g at dec 550 irq 0
de0: DEC 21143 [10-100Mb/s] pass 3.0
de0: address 00:00:f8:75:ba:d3
de0: enabling 10baseT port
pciide0 at pci0 dev 4 function 0: CMD Technology PCI0646 (rev. 0x01)
pciide0: bus-master DMA support present
pciide0: primary channel wired to compatibility mode
atapibus0 at pciide0 channel 0
cd0 at atapibus0 drive 0: <TOSHIBA CD-ROM XM-6102B, 7800327909, 1106> type 5 cdrom removable
cd0: 32-bit data port
cd0: drive supports PIO mode 3, DMA mode 2
pciide0: primary channel interrupting at isa irq 14
cd0(pciide0:0:0): using PIO mode 3, DMA mode 1 (using DMA data transfers)
pciide0: secondary channel wired to compatibility mode
wd0 at pciide0 channel 1 drive 0: <IBM-DPTA-353750>
wd0: drive supports 16-sector pio transfers, lba addressing
wd0: 35772 MB, 16383 cyl, 16 head, 63 sec, 512 bytes/sect x 73261440 sectors
wd0: 32-bit data port
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 4
pciide0: secondary channel interrupting at isa irq 15
wd0(pciide0:1:0): using PIO mode 4, DMA mode 2 (using DMA data transfers)
sio0 at pci0 dev 7 function 0: vendor 0x8086 product 0x0484 (rev. 0x43)
vga0 at pci0 dev 11 function 0: vendor 0x5333 product 0x88c1 (rev. 0x00)
wsdisplay0 at vga0
ppb0 at pci0 dev 20 function 0: vendor 0x1011 product 0x0024 (rev. 0x02)
pci1 at ppb0 bus 1
pci1: i/o space, memory space enabled
isp0 at pci1 dev 8 function 0
isp0: interrupting at dec 550 irq 12
isp0: Ultra Mode Capable
isp0: Board Revision 1040B, loaded F/W Revision 4.65.0
isp0: Last F/W revision was 5.57.1
scsibus0 at isp0: 16 targets, 8 luns per target
ne0 at pci1 dev 9 function 0: RealTek 8029 Ethernet
ne0: 10base2, 10baseT, 10baseT-FDX, auto, default [0x00 0x30] auto
ne0: Ethernet address 52:54:05:f0:bd:1b
ne0: interrupting at dec 550 irq 16
isa0 at sio0
com0 at isa0 port 0x3f8-0x3ff irq 4: ns16550a, working fifo
com0: console
com1 at isa0 port 0x2f8-0x2ff irq 3: ns16550a, working fifo
pckbc0 at isa0 port 0x60-0x64
lpt0 at isa0 port 0x3bc-0x3bf irq 7
fdc0 at isa0 port 0x3f0-0x3f7 irq 6 drq 2
fd0 at fdc0 drive 0: 1.44MB, 80 cyl, 2 head, 18 sec
mcclock0 at isa0 port 0x70-0x71: mc146818 or compatible
scsibus0: waiting 2 seconds for devices to settle...
sd0 at scsibus0 target 0 lun 0: <DEC, RZ1CC-BA (C) DEC, 883F> SCSI2 0/direct fixed
sd0: 4091 MB, 3708 cyl, 20 head, 113 sec, 512 bytes/sect x 8380080 sectors
cd1 at scsibus0 target 4 lun 0: <YAMAHA, CRW4416S, 1.0h> SCSI2 5/cdrom removable
md0: internal 4650K image area
root on md0a dumps on md0b
WARNING: clock gained 56 days -- CHECK AND RESET THE DATE!
root file system type: ffs

fatal kernel trap:

    trap entry = 0x2 (memory management fault)
    a0         = 0xfffffe000239c000
    a1         = 0x1
    a2         = 0x0
    pc         = 0xfffffc000039c6c0
    ra         = 0xfffffc000052eadc
    curproc    = 0xfffffc0000e89180
        pid = 17, comm = mount_ffs

panic: trap

syncing disks... done
rebooting...

[ preserving 178552 bytes of netbsd ELF symbol table ]
Copyright (c) 1996, 1997, 1998, 1999
    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 1.4.1 (AZENOMEI) #27: Wed Jun 14 01:41:57 CEST 2000
    rhialto@azenomei.falu.nl:/usr/src/sys/arch/alpha/compile/AZENOMEI
Digital Personal WorkStation 433au, 432MHz
8192 byte page size, 1 processor.
real mem = 67108864 (2039808 reserved for PROM, 65069056 used by NetBSD)
avail mem = 54288384
using 794 buffers containing 6504448 bytes of memory
mainbus0 (root)
cpu0 at mainbus0: ID 0 (primary), 21164A-0 ()
cia0 at mainbus0: DECchip 2117x Core Logic Chipset (Pyxis), pass 1
cia0: extended capabilities: 1<BWEN>
cia0: using BWX for PCI config access
cia0: WARNING: Pyxis pass 1 DMA bug; no bets...
pci0 at cia0 bus 0
pci0: i/o enabled, memory enabled
de0 at pci0 dev 3 function 0
de0: interrupting at dec 550 irq 8
de0: DEC 21143 [10-100Mb/s] pass 3.0
de0: address 00:00:f8:75:ba:d3
de0: enabling 10baseT port
pciide0 at pci0 dev 4 function 0: CMD Technology PCI0646
pciide0: hardware does not support DMA
pciide0: primary channel wired to compatibility mode
atapibus0 at pciide0 channel 0
cd0 at atapibus0 drive 0: <TOSHIBA CD-ROM XM-6102B, 7800327909, 1106> type 5 cdrom removable
cd0: 32-bits data port
cd0: drive supports PIO mode 3, DMA mode 2
pciide0: secondary channel wired to compatibility mode
wd0 at pciide0 channel 1 drive 0: <IBM-DPTA-353750>
wd0: drive supports 16-sector pio transfers, lba addressing
wd0: 35772MB, 16383 cyl, 16 head, 63 sec, 512 bytes/sect x 73261440 sectors
wd0: 32-bits data port
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 4
cd0(pciide0:0:0): using PIO mode 3
wd0(pciide0:1:0): using PIO mode 4
sio0 at pci0 dev 7 function 0: Intel 82378ZB System I/O (SIO) (rev. 0x43)
vga0 at pci0 dev 11 function 0: S3 86C864-1 ("Vision864") (rev. 0x00)
wsdisplay0 at vga0
ppb0 at pci0 dev 20 function 0: Digital Equipment DECchip 21152 PCI-PCI Bridge (rev. 0x02)
pci1 at ppb0 bus 1
pci1: i/o enabled, memory enabled
isp0 at pci1 dev 8 function 0
isp0: interrupting at dec 550 irq 20
isp0: Ultra Mode Capable
isp0: Board Revision 1040B, loaded F/W Revision 7.55
isp0: Last F/W revision was 5.57
isp0: driver initiated bus reset
scsibus0 at isp0: 16 targets, 8 luns per target
sd0 at scsibus0 targ 0 lun 0: <DEC, RZ1CC-BA (C) DEC, 883F> SCSI2 0/direct fixed
sd0: 4091MB, 3708 cyl, 20 head, 113 sec, 512 bytes/sect x 8380080 sectors
cd1 at scsibus0 targ 4 lun 0: <YAMAHA, CRW4416S, 1.0h> SCSI2 5/cdrom removable
probe(isp0:4:1):  Check Condition on CDB: 0x00 20 00 00 00 00
    SENSE KEY:  No Additional Sense
     ASC/ASCQ:  No Additional Sense Information

probe(isp0:4:2):  Check Condition on CDB: 0x00 40 00 00 00 00
    SENSE KEY:  No Additional Sense
     ASC/ASCQ:  No Additional Sense Information

probe(isp0:4:3):  Check Condition on CDB: 0x00 60 00 00 00 00
    SENSE KEY:  No Additional Sense
     ASC/ASCQ:  No Additional Sense Information

probe(isp0:4:4):  Check Condition on CDB: 0x00 80 00 00 00 00
    SENSE KEY:  No Additional Sense
     ASC/ASCQ:  No Additional Sense Information

probe(isp0:4:5):  Check Condition on CDB: 0x00 a0 00 00 00 00
    SENSE KEY:  No Additional Sense
     ASC/ASCQ:  No Additional Sense Information

probe(isp0:4:6):  Check Condition on CDB: 0x00 c0 00 00 00 00
    SENSE KEY:  No Additional Sense
     ASC/ASCQ:  No Additional Sense Information

probe(isp0:4:7):  Check Condition on CDB: 0x00 e0 00 00 00 00
    SENSE KEY:  No Additional Sense
     ASC/ASCQ:  No Additional Sense Information

ne0 at pci1 dev 9 function 0: RealTek 8029 Ethernet
ne0: 10base2, 10baseT, 10baseT-FDX, auto, default auto
ne0: Ethernet address 52:54:05:f0:bd:1b
ne0: interrupting at dec 550 irq 24
isa0 at sio0
com0 at isa0 port 0x3f8-0x3ff irq 4: ns16550a, working fifo
com0: console
com1 at isa0 port 0x2f8-0x2ff irq 3: ns16550a, working fifo
lpt0 at isa0 port 0x3bc-0x3bf irq 7
sb0 at isa0 port 0x220-0x237 irq 5 drq 1: dsp v3.01
midi0 at sb0: <SB MIDI UART>
audio0 at sb0: half duplex
opl0 at sb0: model OPL3
midi1 at opl0: <SB Yamaha OPL3>
sb: can't map i/o space 0x220/24 in probe
pckbc0 at isa0 port 0x60-0x64
pcppi0 at isa0 port 0x61
spkr0 at pcppi0
isabeep0 at pcppi0
fdc0 at isa0 port 0x3f0-0x3f7 irq 6 drq 2
fd0 at fdc0 drive 0: 1.44MB, 80 cyl, 2 head, 18 sec
mcclock0 at isa0 port 0x70-0x71: mc146818 or compatible
root on sd0a dumps on sd0b
isp0: Target 0 at 20MHz Max Offset 8, 16 bit wide, Tagged Queueing Enabled
root file system type: ffs
IP Filter: initialized.  Default = pass all, Logging = enabled
de0: enabling 100baseTX port

-Olaf.
-- 
___ Olaf 'Rhialto' Seibert - rhialto@polder --Soep van de dag, wat zal dat zijn
\X/ land.nl     --wat kan dat wezen, beter maar het ergste vrezen -Boy Bensdorp