Readme as supplied by ZyXEL:

(1) Environment Setup:
    a. Install Ubuntu 12.04.5 LTS.
    b. Get root privilege.
        # sudo su
        # <password>
    c. Synchronize the package index files.
        # apt-get update
    d. Install toolchain.
        # apt-get install build-essential subversion git-core libncurses5-dev zlib1g-dev gawk flex quilt libssl-dev xsltproc libxml-parser-perl mercurial bzr ecj cvs libglib2.0-dev
    e. Create the symbolic link that point sh to bash.
        # rm /bin/sh
        # ln -s /bin/bash /bin/sh
    f. Extract and decompress bz2 file of source code.
        # tar jxvf <FileName>.tar.bz2
    g. Move to GPL working directory.
        # cd vmg1312_release/

(2) Build Source Code:
        # make clean
        # make

(3) Image File: bin/brcm963xx/zyxel/ras.bin