map 问题"due to having no input or output PAD connections .."

Pack:198 - NCD was not produced. All logic was removed from design.
This is usually due to having no input or output PAD connections in the design and no nets or symbols marked as 'SAVE'.
You can either add PADs or 'SAVE' attributes to the design, or run 'map -u' to disable logic trimming in the mapper.

ise map时出现上述错误退出，但我的设计有输入输出信号啊，怎么被remove了?