[U-Boot] u-boot was skipped: because UBOOT_MACHINE is not set

Hi all,

I am trying to buildhttp://gumstix.org/software-development/yocto-project.html a bitbake target for my RobOvero board.I get this following error: "*ERROR: u-boot was skipped: because UBOOT_MACHINE is not set*"

How do I set values and build uboot for Overo Series RobOvero board(PCB 30019-R3277)

Thank You.