今天实验调试时之前一直好好的，突然程序下载不进去了，烧写FPGA的bit文件出现如下报错：
ERROR:Bitstream:2 - The input file "E:\XXX.msk" does not exist. Please check that the specified location is correct and that the bitstream was succesfully created.
ERROR:iMPACT:123 - Mask file E:\XXX.msk is invalid
因为之前从来没有遇到这样的问题，一下子有点懵了，回家google了下，找到比较靠谱的答案：
The -v option you use is to have a Verify carried out on the design after programming. This is where iMPACT will read back the configuration data to determine if the device has been programmed correctly. The .msk file is used to mask out teh dynamic values in the design whiach may have changed. If you have not generated this file or it is not in the directory specified for the bit file you get this error. You can either not use teh -v option or ensure you have the correct .msk file. The ,msk fiel is generated by using the "Create Readback Data files" and "Create Mask File" options in bitgen (-m).
所以：
1，去掉烧写时的Verify。
2，bitgen -m
