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Normally, one would used "boot -c" to disable ACPI prior to kernel probes; it looks like, for some reason, the kernel isn't even getting far enough to do that.
Some things to try, knowing none may work:
- booting the MP kernel
- disabling ACPI in /bsd and /bsd.mp kernel while running from the ramdisk kernel, then trying both again.
- trying a recent snapshot.
To do #2, here are step-by-step instructions. Assuming wd0a is your root partition, and wd0d is your /usr partition. Adjust accordingly. The config program resides in /usr/sbin, and it uses dynamic libraries reside in /usr/lib and /usr/libexec. You'll engage the program via a chroot(8) shell, which will make the /mnt directory "/" until you exit.
Boot bsd.rd (or the install cd), select the shell, then:
# mount /dev/wd0a /mnt
# mount /dev/wd0d /mnt/usr
# /mnt/usr/sbin/chroot /mnt ksh
# config -ef /bsd
# config -ef /bsd.mp
# exit
From config's ukc> prompts: use "disable acpi" then "quit" to disable acpi in the UP and MP kernels.