esp32生成makefile的时候，始终提示出错，为什么？

我买了个esp32的开发板，我下载sdk只有，
在执行cmake .
来生成makefile的时候，始终提示出错，
错误提示如下：
CMake Error at tools/cmake/kconfig.cmake:76 (file):
  file problem creating directory: /config
Call Stack (most recent call first):
  CMakeLists.txt:68 (kconfig_process_config)


CMake Error at CMakeLists.txt:71 (include):
  include could not find load file:

    /config/sdkconfig.cmake


CMake Error at tools/cmake/idf_functions.cmake:204 (message):
  Internal error, toolchain has not been set correctly by project (or an
  invalid CMakeCache.txt file has been generated somehow)
Call Stack (most recent call first):
  CMakeLists.txt:74 (idf_verify_environment)


-- Configuring incomplete, errors occurred!
See also "/home/lu/pro/esp32/esp-idf-master/CMakeFiles/CMakeOutput.log".
请问下是什么原因