vivado2017.4生成比特流失败，报错信息：
- [Drc 23-20] Rule violation (NSTD-1) Unspecified I/O Standard - 4 out of 142 logical ports use I/O standard (IOSTANDARD) value ‘DEFAULT’, instead of a user assigned specific value. This may cause I/O contention or incompatibility with the board power or connectivity affecting performance, signal integrity or in extreme cases cause damage to the device or the components to which it is connected. To correct this violation, specify all I/O standards. This design will fail to generate a bitstream unless all logical ports have a user specified I/O standard value defined. To allow bitstream creation with unspecified I/O standard values (not recommended), use this command: set_property SEVERITY {Warning} [get_drc_checks NSTD-1]. NOTE
- When using the Vivado Runs infrastructure (e.g. launch_runs Tcl command), add this command to a .tcl file and add that file as a pre-hook for write_bitstream step for the implementation run. Problem ports: USBIND_0_port_indctl[1:0], USBIND_0_vbus_pwrfault, USBIND_0_vbus_pwrselect.
解决办法：
新建记事本，添加以下三句：
set_property SEVERITY {Warning} [get_drc_checks NSTD-1]
set_property SEVERITY {Warning} [get_drc_checks RTSTAT-1]
set_property SEVERITY {Warning} [get_drc_checks UCIO-1]
重命名为 name.tcl文件（确定后缀格式有效）
在进入vivado软件，在generate bitstream 界面如下，右键进入setting
点击tcl.pre
选中刚才配置的name.tcl
点击OK，就行了，之后就可以成功生成bit流了。
来源：CSDN
作者：yohe12
链接：https://blog.csdn.net/yohe12/article/details/104790430