FreeBSD 5.3p6-5.4RC3, Supermicro X6DHR-8G, Dual 3.6GHz Xeons,Adaptec aic7902 SCSI interface doesn't work in UP kernel

[Guy Helmer]

I have SuperMicro X6DHR-8G machines with dual 3.6GHz Xeons and a Seagate 
73G drive attached to the on-board aic7902 SCSI channel.  A uniprocessor 
FreeBSD 5.3p6 or 5.4RC3 kernel booted on this machine stops at the SCSI 
bus probe for a minute or so, and then occasionally spews messages 
"SIMOE0[0xc]: (ENOVERRUN|ENIOERR)" followed by more info and finally 
"Issued Channel A Bus Reset, <n> SCBs aborted".  It never seems to get 
past this point.

I've tried both BIOS revisions 1.2 and 1.2a with no effect on the errors.
Disabling ACPI seemed to have no effect on the errors.
Disabling the APIC allowed it to boot successfully.
Booting an SMP kernel allows it to boot successfully (this is the 
obvious workaround, but the problem was first discovered when trying to 
boot from a GENERIC UP kernel on CD-ROM; booting 5.4-RC3 Disc 1 hangs 
the same way unless I boot in "Safe" mode).

dmesg (from a successful boot), mptable, and "acpidump -t -d" output are 
available if anyone cares to look:

http://www.palisadesys.com/~ghelmer/X6DHR-8G-dmesg.txt
http://www.palisadesys.com/~ghelmer/X6DHR-8G-mptable.txt
http://www.palisadesys.com/~ghelmer/X6DHR-8G.asl

If there is anything else I can provide that will help diagnose the 
problem, please let me know.

Guy

-- 
Guy Helmer, Ph.D.
Principal System Architect
Palisade Systems, Inc.