Build Process

1. You need to get the latest Source-Tree with subversion:
   # pkg install subversion
   # svn co https://svn0.us-west.freebsd.org/base/head /usr/src
   Subversion is a version control system, which allows you to keep old versions of files and directories (usually source code), keep a log of who, when, and why changes occurred, etc., like CVS, RCS or SCCS. Subversion keeps a single copy of the master sources. This copy is called the source repository, it contains all the information to permit extracting previous versions of those files at any time.
   If something goes wrong and you must to it again first issue this command:
   # svn cleanup /usr/src/
2. Now it’s time to get Crochet to build our image:
   # pkg install git-2.13.0
   # git clone https://github.com/freebsd/crochet.git
3. Select which board you want to build for:
   # cd crocket
   # cp config.sh.sample config.sh.rpi3
   # ee config.sh.rpi3
   uncomment this line 38 and exit:
   board_setup RaspberryPi3
4. Build the image:
   # pkg install u-boot-rpi3-2017.01
   Cross-build U-Boot loader for RPi3
   Das U-Boot (subtitled “the Universal Boot Loader” and often shortened to U-Boot) is an open-source, primary boot loader used in embedded devices to package the instructions to boot the device’s operating system kernel. It is available for a number of computer architectures, including 68k, ARM, AVR32, Blackfin, MicroBlaze, MIPS, Nios, SuperH, PPC, RISC-V, and x86.
   U-boot-rpi3 is a Cross-build U-Boot loader for Rpi3.
   # ./crochet.sh -c config.sh.rpi3
   The build process depends on your CPU speed but in general needs a lot of time.

You can get full edition at:
https://bsdmag.org/download/creating-scaling-applications-using-containerpilot-pattern/
Or:
https://contents.meetbsd.ir/ebook/rpi3_Freebsd12_bsdmag.pdf