1) checkout armv6
2) apply http://people.FreeBSD.org/~cognet/bapt-patch.diff
3) build a kernel toolchain (from the armv6 sourcetree, make TARGET_ARCH=arm kernel-toolchain)
4) build the kernel (make TARGET_ARCH=arm KERNCONF=PANDABOARD buildkernel) (if you plan to boot from an USB stick instead of NFS, remove the BOOTP/NFSROOT from the kernel config file, and add the relevant ROOTDEVNAME instead)
5) get omap4loader from here : http://web.me.com/dmarion/omap4loader/, build it, and download the aboot.bin when loading from 0x80200000
6) ./omap4loader aboot_0x80200000.bin /path/to/the/kernel/kernel.bin
At this point, you'll see the kernel babbling on the serial console, and eventually die because it failed to find a root
7) build a root ! make TARGET_ARCH=arm TARGET_CPUTYPE=xscale buildworld (xscale is a bit unoptimal, like building for i586 is a bit unoptimal for modern cpus)
8) if you're going to use NFSROOT, make TARGET_ARCH=arm TARGET_CPUTYPE=xscale DESTDIR=/path/to/your/nfsroot installworld, if you plan to use an USB stick, just install what you want on the stick
9) If you plan to boot using NFSROOT, setup a nfs and a bootp server
10) Beware, your new root needs a feeled /etc ! passwd stuff is a must, you probably want to copy src/etc.arm/ttys as /etc/ttys, as well)
11) If all went well, you're now able to boot multiuser