Re: [Iverilog-devel] need a language-lawyer ruling and/or a bug fix

[Larry D. <ldo...@re...>]

Cary -

On Wed, Apr 02, 2008 at 02:29:45PM -0700, Cary R. wrote:
> --- Larry Doolittle <ldo...@re...> wrote:
>  
> > The attached code shows a change in behavior in recent
> > (as of March 20) git.  It triggered a failure in my
> > inverse regression test.  I need to know if my Verilog
> > assumptions are wrong, or the new Icarus behavior is wrong.
> 
> This does seem to be slightly incorrect. Section 3.6 in 1364-2001 implies
> that the initial value should be z, but then the driver value should
> propagate. Given that this hasn't happened after #10 implies that the x is
> not propagating after the initial z.

Icarus, both before and after the patch in question,
gives "x" for the uninitialized fdbk_err_wide (sorry
about the strange names, this was stripped from a larger
code base and I didn't bother to change names).

The behavior change is how "x" propagates through the ternary
expression.  The old result (that I expect) is it comes out "x".
After the commit in question, it comes out "z".

I din't try to isolate this to a particular mux input; in this
case all three mux inputs are derived from fdbk_err_wide.  My
wild guess is that the confusion comes from the control input
to the mux.

   - Larry