Vivado进行Generate Bitstream时报错 [Drc 23-20]

在做OFDM项目上Zedboard验证时出现的问题，所有的输入输出接口没有被全部约束就会报错，如下：

[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.

[Drc 23-20] Rule violation (UCIO-1) Unconstrained Logical Port - 4 out of 142 logical ports have no user assigned specific location constraint (LOC). 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 pin locations. This design will fail to generate a bitstream unless all logical ports have a user specified site LOC constraint defined.  To allow bitstream creation with unspecified pin locations (not recommended), use this command: set_property SEVERITY {Warning} [get_drc_checks UCIO-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.

根据提示在 srcs文件夹下新建pre.tcl文件，在文件中添加：

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]

在Bitstream Setting中tcp.pre一栏添加该tcl文件，问题解决了

当然，问题的原因是有一部分I/O接口没有被写入约束中，也可以将所有I/O口写入约束来解决