Uboot build Failure

I have just dowloaded the Android Pie source code
Trtying to build UBoot results in

/Vim3Android/bootloader/uboot# ./mk TARGET
Clean up
CLEAN scripts/basic
CLEAN scripts/kconfig
CLEAN .config
Compile config: TARGET
HOSTCC scripts/basic/fixdep
GEN ./Makefile

*** Can’t find default configuration “configs/TARGET_defconfig”!

/home/rowland/Vim3Android/bootloader/uboot/Makefile:480: recipe for target ‘TARGET_config’ failed
make[1]: *** [TARGET_config] Error 1
Makefile:147: recipe for target ‘sub-make’ failed
make: *** [sub-make] Error 2
Pre-build failed! exit!

I succeded in building the code about 3 weeks ago. But I tried on a different PC and got the above error. I then tried again on my old PC (The one that succeeded three weeks ago) and again got the same error.

You should look at the document more carefully