amd64/182740: BTX halted on Jetway NF81 motherboard when RAID is enabled

[Julian Pidancet]

>Number:         182740
>Category:       amd64
>Synopsis:       BTX halted on Jetway NF81 motherboard when RAID is enabled
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-amd64
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Oct 06 11:30:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator:     Julian Pidancet
>Release:        8.2
>Organization:
>Environment:
>Description:
Just got this brand new motherboard with an AMD APU and an AMD chipset.

Whenever I try to boot FreeBSD and AHCI or RAID is enabled in the BIOS, I am getting this message:

BTX loader 1.00  BTX version is 1.02
int=0000000a  err=00000000  efl=00006402  eip=000093e0
eax=534d4150  ebx=00000001  ecx=00000014  edx=534d4150
esi=00000000  edi=00000004  ebp=00000000  esp=0000004e
cs=0008  ds=0033  es=0033    fs=0033  gs=0033  ss=0010
cs:eip=cf 83 f8 01 75 1a 16 87-86 1f 1e 0f a1 0f a0 0f
       a9 b8 00 a0 00 00 03 44-24 0c 8d 60 04 58 ff d0
ss:esp=00 f0 39 e7 00 f0 e3 21-80 ce 2e e8 00 f0 d2 ef
       00 f0 00 e0 00 f0 f2 e6-00 f0 6e fe 00 f0 53 ff
BTX halted

It looks like to me the BTX is taking an "Invalid TSS" exception while executing an iret instruction.
>How-To-Repeat:
I tried: - Booting from the install cdrom
         - Booting from an USB install disk
         - Booting from boot/pxeboot in PXE mode

All exhibit the same issue.
>Fix:
Selecting "Legacy IDE" mode in the BIOS configuration instead of AHCI/RAID.

>Release-Note:
>Audit-Trail:
>Unformatted: