[U-Boot] [compile error] No rule to make target '.depend', needed by libul2410.a

[yihect]

 Hi all, I want to used u-boot for my linux port. 
 
 Accroding from content of file README in u-boot-1.3.4 package, I have did follows:
 1, vi Makefile, add one new entry for my ul2410 board;
 2, create a directory (board/ul2410) by:
         cp -rf ./board/smdk2410  ./board/ul2410
         cd ./board/ul2410
         mv  ./smdk2410.c  ./ul2410.c
 3, and create a new config file by:
         cp include/boards/smdk2410.h  include/boards/ul2410.h
 
 Finally, I config it:
 
 $make CROSS_COMPILE=arm-9tdmi-linux-gnu- ul2410_config
 Configuring for ul2410 board...
 $
 
 and than compile it:
 
 $make CROSS_COMPILE=arm-9tdmi-linux-gnu- 
 
 make does his work correctly unti error present as follow:
 
 ...
make[1]: Leaving directory '/home/yihect/.../u-boot-1.3.4/post'
make -C board/ul2410/
make[1]:Entering direcotory '/home/.../board/ul2410'
make[1]:*** No rule to make target '.depend', needed by 'libul2410.a'. Stop.
make[1]:Leaving directory.....
make: *** .... Error 2
$
 
 After catting the Makefile in /board/ul2410 dir, it seems that the $(obj)  is expanded to some blank space. That's why?
 
 I'm still a newbie to makefile, so can anybody help me? Any suggestion is appericated too. Thanks.