> > Could you try using the cmdide driver instead of pciide ?
> 
> Added:
> 	cmdide* at pci? dev ? function ? flags 0x0000
> 
> Result:
> 
> cmdide0 at pci0 dev 11 function 0
> cmdide0: CMD Technology PCI0646 (rev. 0x01)
> cmdide0: bus-master DMA support present
> cmdide0: primary channel wired to compatibility mode
> cmdide0: primary channel interrupting at isa irq 14
> atabus2 at cmdide0 channel 0
> cmdide0: secondary channel wired to compatibility mode
> cmdide0: secondary channel interrupting at isa irq 15
> atabus3 at cmdide0 channel 1
> isa0 at sio0
> 
> [ ... ]
> 
> satalink0: port 1: device present, speed: 1.5Gb/s
> wd0 at atabus1 drive 0scsibus0: waiting 2 seconds for devices to settle...
> : <ST3250823AS>
> wd0: drive supports 16-sector PIO transfers, LBA48 addressing
> wd0: 232 GB, 484521 cyl, 16 head, 63 sec, 512 bytes/sect x 488397168 sectors
> 
> unexpected machine check:
> 
>     mces    = 0x1
>     vector  = 0x670
>     param   = 0xfffffc0000006068
>     pc      = 0xfffffc00004f4b74
>     ra      = 0xfffffc00004e0688
>     code    = 0x98
>     curlwp = 0xfffffc0000ade870
>         pid = 10.1, comm = atabus3
> 
> panic: machine check
> syncing disks... done
> rebooting...
> 
> Note that wd0 is a SATA disk on its own SATA controller, not the PATA one
> connected to the CMD.
> 
> I can talk to the disk by sticking it into a USB-to-PATA external box,
> until it hits an unreadable sector which then seems to require
> a power cycle.  There are some corrupted sectors as well as unreadable ones.
> 
> Haven't been able to get fsck to complete, due to the unreadable sector
> problem.  Haven't tried letting it run overnight, maybe it would eventually
> time out or exhaust some retry counter?
> 
> Are there any diagnostics for the CMD PATA controller?
> I'm beginning to wonder if some smoke came out when I wasn't looking.

More data:

I get the same machine check with a CD/DVD drive attached instead of the
hard drive.

With no drive attached, it boots up okay.

Without cmdide configured into the kernel it boots okay,
even with a drive attached, but doesn't configure the drive.

Ideas?  I'm running out of things to try.