Powerpc based FreeBSD Compilation

[U Bhaskar-B22300]

Hi All,
                I want to compile FREEBSD Kernel on powerpc
                I am using Ubuntu as my development system and I am having the powerc tool chain, While compiling, I am getting the below error.

root at test-VirtualBox:/usr/src# bmake
bmake: no system rules (sys.mk).

bmake: stopped in /usr/src

What is this error ?

1. Can I compile FreeBSD on Ubuntu system.
2. Do I need the iso or src.tgz for FreeBSD compilation

Regards
--Bhaskar