vhdl进程中的敏感性列表留空xilinx合成工具会显示错误

gopalkrishnarn写道：
我在vhdl书中读过，如果vhdl进程中的灵敏度列表留空，则进程无限期执行，但如果我将灵敏度列表留空，则xilinx合成工具会显示错误。所以我在灵敏度列表中放入一个虚拟输入位信号
并且据我所知，只有当灵敏度列表上有事件时，才会执行该过程。但在modelsim中，默认情况下该位信号的值为0，然后即使不改变它的值，模拟工作正确并且处理执行
。
这怎么可能 ？
您可能会在没有敏感列表的流程中看到错误，因为您的代码没有“等待”发生某些事情的逻辑。
具有敏感性列表的过程仅在该列表中的信号发生变化时触发。
对于注册过程，唯一感兴趣的信号是时钟（想想D触发器）。
对于组合过程，您必须考虑所有分配右侧的每个信号。
拥有没有敏感性列表的流程当然是合法的。
但是，这种过程必须有某种延时或等待机制;
否则进程将尝试在零时间内循环。
请购买Peter Ashenden的“VHDL设计师指南”。
它将为您澄清所有这些。
----------------------------是的，我这样做是为了谋生。



以下为原文

 

gopalkrishnarn wrote:
I have read in a vhdl book that if the sensitivity list in vhdl process is left blank the process executes indefinitely but if i leave the sensitivity list blank, the xilinx synthesize tool shows error.So i put a dummy input bit signal in the sensitivity list and as far as i know the process executes only when there is a event on the sensitivity list.But in modelsim it takes by default the value as 0 for this bit signal and then even if dont change it's value the simulation works correct and process executes.


How is this possible ?

 
You are likely seeing errors in processes without a sensitivity list because your code has no logic that "waits" for something to happen.
 
A process that HAS a sensitivity list will only trigger on a change in the signals in that list. For a registered process, the only signal that is of interest is the clock (think about a D flip-flop). For a combinatorial process, you must consider EVERY signal on the right-hand side of all assignments.
 
It is certainly legal to have a process without a sensitivity list. However, this sort of process must have some kind of time-delay or wait mechanism; otherwise the process will try to loop in zero time.
 
Please please please buy a copy of Peter Ashenden's "The Designer's Guide To VHDL." It will clarify all of this for you.
----------------------------Yes, I do this for a living.

无论如何，进程无限期地执行。
您看到的错误消息可能是一个警告，说合成器检测到列表中缺少的信号并自动添加它们。
我见过很多合成器都是这样做的。
吉姆



以下为原文

A process executes indefinitely anyway.
The error message you saw is probably a warning saying that the synthesizer detected signals missing from the list and is adding them automatically.  I have seen many synthesizers that do this.
Jim
 

嗨，
关于敏感性列表和过程需要记住的一些事项：
- 它们仅用于模拟并被合成忽略，即使某些工具发出警告（主要是告诉您模拟可能不准确）
- 在0时刻触发所有进程一次
- 如果没有敏感列表，进程必须至少有一个wait语句，否则它会无限重启并且你的模拟器会停止。
发布您的代码，以便我们为您提供有关其工作原理的更多具体信息。
有一个很好的模拟 
Eilert



以下为原文

Hi,some things to remember about sensitivity lists and processes:- They are only used in simulation and ignored by synthesis, even if some tools give warnings (mostly to tell you that the simulation may be inaccurate)- ALL processes are triggered once at time 0- Without a sensitivity list a process has to have at least one wait-statement, otherwise it restarts infinitely and your simulator stalls.Post your code, so we can give you more specific information about how it works.Have a nice simulation  Eilert