[U-Boot-Users] [for clues] No rule to make target .depend

Hi all, I am newbie. I am trying to port u-boot to my board. I did these things: 1. copy a existing board directory, say m5445evb, to a new one "mercury" 2. copy the M5445X_config section and rename it to "MERCURY_config" 3. change board name "m5445evb" in the "@mkconfig -a ..." line to mercury but when I try to compile u-boot make says "no rule to make target .depend", needed by lib_mercury.a in the board/freescale/mercury directory. I can compile u-boot for m5445evb normally. What's the matter?