--- Quote Start ---
For simple reasons already explained by others, if you can't specify a timing relation between a and b input,
no tool will be able to perform a timing analysis. You have to exepect glitches at c. If c is only clocking a single FF as in your example, there are probably no consequences for your design, otherwise you should be cautious.
As an additional remark: The problems brought on by such designs are typically more serious with rare timing violation events. You don't see them in a test, but the system reveals unreliable in operation at customer site.
--- Quote End ---
Thank you for reminding, FvM!
In my design,just as you said,the c is only clocking a single FF.
when a or b changed, the "out" must flip,i don't know how to achive it except the way i posted.
Honored Contributor
