Current pieSense image status:

Install FreeBSD 11.2-RELEASE (amd64) on a machine with at least 25GB of hard disk (UFS partition) and at least 4GB of RAM to successfully build armv6 image. All tasks require a root user.

Install git, qemu-user-static, arm-gnueabi-binutils, u-boot-rpi2 and rpi-firmware

# pkg install git qemu-user-static arm-gnueabi-binutils u-boot-rpi2 rpi-firmware

Grab OPNsense/tools repositories (overwriting standard ports and src)

# cd /usr && git clone https://github.com/opnsense/tools
# cd tools
# make update
# sed -i -e 's/${_ARCH}/arm:armv6/1' Makefile
# sed -i -e 's/a10/rpi2/1' Makefile

Make armv6 image for RPI2

# make base 
# make kernel
# make xtools
# make packages
# make arm-3G

Your pieSense is there if successfully built

# make print-IMAGESDIR

Flash pieSense image to MicroSD card with your favourite tool. Eg: dd, Win32DiskImager.

Enjoy using your unofficial build of OPNsense. Stay safe.