发布于 2014-09-05  3.41k 次阅读

1."WARNING:Route:455 - CLK Net:trn_clk_OBUF may have excessive skew because 0 CLK pins and 1 NON_CLK pins failed to route using a CLK template."


This message informs the user that some loads on the clock net are not clock pins. Therefore, the clock template that is normally used to connect clock pins will not be used to connect the loads. A different routing that involves local routing will be used, potentially inducing some skew on the clock net. Opening your design in FPGA EDITOR will allow you to see what loads are connected to the clock net, and the cause of the warnings. The amount of skew on the net will be reported in the Place and Route report. If the loads on the net shown in FPGA Editor are in accord with your design, the skew reported in the PAR report is not critical for the design, and the timing constraint requirement on that net is met, then this warning can be safely ignored.

实例原因:在代码中用到这样的语句时(aa’event and aa=’1’),aa不是时钟信号,最多只是时钟信号产生的一类周期信号,aa被作为了另一个进程或模块的类似周期信号的作用。(我是在行场信号发生器中出现的这样的问题,用产生的行同步信号(行同步信号是由全局时钟信号驱动产生的)再去驱动产生场同步信号,产生的场同步信号相对与输入的全局时钟,有一定 的倾斜)

  1. "WARNING:Xst:647 - Input <name> is never used." or

"WARNING:Xst:648 - Output <name> is never used."


This particular port has been declared in your HDL description, but does not drive or is not driven by any internal logic. Unused input ports will remain in the design, but they will be completely unconnected. If the port is not intended to be used, this message can be safely ignored. To avoid this message, remove any loadless or sourceless elements from your HDL description. Output ports will remain in the final netlist and will be driven by a logic 0. To avoid the message and to save the port resource, remove the unused output port from your HDL description.

实例原因:一般输入端口不要预留,即使不使用,在代码中定义的输入端口就一定要有输入的;而输出端口不用到的可以用OPEN封上,最常见的是在利用DLL和DCM时,CLK90,CLK180, CLK270等一般不用,在端口连接的时候都用OPEN封上。

  1. ERROR:HDLParsers:3562 - pepExtractor.prj line 1 Expecting 'vhd ' or 'verilog' keyword, found 'work'。SolutionThis occurs when there are spaces embedded in the project location. A bad example for project location would be: C:/Documents and Settings/User/example.ise. A good example fpr project location would be: C:/ISE_tests/example.ise.


  1. "ERROR:Xst:2587 Port <port_name> of instance <inst_name> has different type in definition <def_name>" .


Compare the component declaration and instantiation to the submodule that is instantiated. When this error occurs, the declaration matches the instantiation, but does not match the port declarations of the submodule. Change either the port declarations in the declaration/instantiation pair or the submodule port declarations so that they match. This error is specific to the types of ports in the submodule.

实例原因:一般是子模块宣称和子模块的实体定义中端口的宽度和类型(in, out, inout, buffer)不匹配造成的。

  1. XST can generate very large log files for certain designs. In some cases, the generation of these log files can even cause an increase in runtime. How can I eliminate or hide certain frequently generated messages?


For users of XST via Project Navigator Starting in ISE 7.1i, Project Navigator has the capability to do message filtering for all Xilinx tools. Please refer to the Project Navigator help on how to use this method. For users of XST via command line You can hide specific messages generated by XST at the HDL or Low-Level Synthesis steps in specific situations by using the XIL_XST_HIDEMESSAGES environment variable. This environment variable can have one of the following values:

-- none: maximum verbosity. All messages are printed out. This is the default.

-- hdl_level: reduce verbosity during VHDL/Verilog Analysis and HDL Basic and Advanced Synthesis.

-- low_level: reduce verbosity during Low-level Synthesis

-- hdl_and_low_levels: reduce verbosity at all stages

The following messages are hidden when hdl_level or hdl_and_low_levels values are specified for the XIL_XST_HIDEMESSAGES environment variable:

WARNING:HDLCompilers:38 - design.v line xx Macro 'my_macro' redefined

NOTE: This message is issued by the Verilog compiler only.

WARNING:Xst:916 - design.vhd line xx: Delay is ignored for synthesis.

WARNING:Xst:766 - design.vhd line xx: Generating a Black Box for component comp. Instantiating component comp from Library lib. Set user-defined property "LOC = X1Y1" for instance inst in unit block. Set user-defined property "RLOC = X1Y1" for instance inst in unit block. Set user-defined property "INIT = 1" for instance inst in unit block. Register reg1 equivalent to reg2 has been removed.

The following messages are hidden when low_level or hdl_and_low_levels values are specified for the XIL_XST_HIDEMESSAGES environment variable:

WARNING:Xst:382 - Register reg1 is equivalent to reg2.

Register reg1 equivalent to reg2 has been removed.

WARNING:Xst:1710 - FF/Latch reg (without init value) is constant in block block.

WARNING:Xst 1293 - FF/Latch reg is constant in block block.

WARNING:Xst:1291 - FF/Latch reg is unconnected in block block.

WARNING:Xst:1426 - The value init of the FF/Latch reg hinders the constant cleaning in the block block. You could achieve better results by setting this init to value.


  1. "WARNING:Xst:737 - Found n-bit latch for signal <name>." The listing for "n" is the width of the latch. If latch inference is intended, you can safely ignore this message. However, some inefficient coding styles can lead to accidental latch inference. You should analyze your code to see if this result is intended. The examples below illustrate how you can avoid latch inference.


Solution 1:

Include all possible cases in the case statement

These two examples create latches because there is no provision for the case when SEL = "11." To eliminate the latches, add another entry to deal with this possibility.

Using the "DEFAULT" (Verilog) or "WHEN OTHERS" (VHDL) clause always works, but this can create extraneous logic. This is always the safest methodology, but might produce a larger and slower design since any unknown state has logic that is needed to bring it to a known state.

Solution 2:

Assign to all the same outputs in each case.

These examples infer latches because the "11" case assigns two outputs, while the others assign only one. Looking at this case from TEMP's point of view, only one of four possible cases are specified, so it is incomplete. You can avoid this situation by assigning values to the exact same list of outputs for each case.

Solution 3:

Make sure any "if / else if" statements have a concluding "else" clause:


7.ERROR:Place:1018 - A clock IOB / clock component pair have been found that are not placed at an optimal clock IOB / clock site pair. The clock component <CLK16_inst> is placed at site <BUFGMUX_X0Y3>. The IO component <Ref_Clk_p> is placed at site <A8>.  This will not allow the use of the fast path between the IO and the Clock buffer. If this sub optimal condition is acceptable for this design, you may use the CLOCK_DEDICATED_ROUTE constraint in the .ucf file to demote this message to a WARNING and allow your design to continue. However, the use of this override is highly discouraged as it may lead to very poor timing results. It is recommended that this error condition be corrected in the design. A list of all the COMP.PINs used in this clock placement rule is listed below. These examples can be used directly in the .ucf file to override this clock rule. < NET "Ref_Clk_p" CLOCK_DEDICATED_ROUTE = FALSE; >


8.WARNING:PhysDesignRules:781 - PULLUP on an active net. PULLUP of comp Flash_rst_n is set but the tri state is not configured. Your problem is in the source code,not your constraints. It's complainingthat you don't ever tristate the signal, either because your equations don't have a tristate term or because that term has been optimised away.


9.WARNING:PhysDesignRules:372 - Gated clock. Clock net AD_RD_N_OBUF is sourced by a combinatorial pin. This is not good design practice. Use the CE pin to control the loading of data into the flip-flop.