#993 Synthesis does not support some common styles for coding flip-flops

[Larry Doolittle]

$ iverilog -V | grep "version 1"
Icarus Verilog version 11.0 (devel) (s20150603-96-g19009ec)
Icarus Verilog Preprocessor version 11.0 (devel) (s20150603-96-g19009ec)
Icarus Verilog Parser/Elaborator version 11.0 (devel) (s20150603-96-g19009ec)
$ iverilog -Wall mp_proc.v
$ iverilog -Wall mp_proc.v -t sizer
mp_proc.v:8: warning: Process not synthesized.
mp_proc.v:8: warning: Process not synthesized.
mp_proc.v:8: warning: Process not synthesized.
ivl: t-dll.cc:1062: virtual void dll_target::logic(const NetLogic*): Assertion `nex->t_cookie()' failed.
Aborted

This example stripped down from working, tested production code.

[Martin Whitaker]

I've pushed a temporary fix for this to both the master and v10 branches, that outputs a "sorry" message instead of an assertion failure. Currently synthesis does not support the styles of coding flip-flops that use multiple statements, e.g.

q <= 0;
if (a) q <= d;

or

if (clr) q <= 0;
if (set) q <= 1;

I don't think it would be too hard to support this - but I'm out of time tonight. I'll change the bug title to reflect where we are now.

[Stephen Williams]

This will probably be a bit much for a stable branch, so I'd
say to not worry about porting into the v10 branch.

On 02/21/2016 03:41 PM, Martin Whitaker wrote:

• status: open --> closed-fixed
• Comment:

Well, it turned out to be quite a bit harder than I thought, but this is
now fixed in the master branch. This could be back-ported to v10, but
I'll leave it to mature a bit first.

---

[bugs:#993] http://sourceforge.net/p/iverilog/bugs/993/ Synthesis
does not support some common styles for coding flip-flops

Status: closed-fixed
Group: devel
Created: Thu Aug 20, 2015 08:35 PM UTC by Larry Doolittle
Last Updated: Sat Jan 30, 2016 10:54 PM UTC
Owner: nobody
Attachments:

• mp_proc.v
  https://sourceforge.net/p/iverilog/bugs/993/attachment/mp_proc.v
  (356 Bytes; application/octet-stream)

$ iverilog -V | grep "version 1"
Icarus Verilog version 11.0 (devel) (s20150603-96-g19009ec)
Icarus Verilog Preprocessor version 11.0 (devel) (s20150603-96-g19009ec)
Icarus Verilog Parser/Elaborator version 11.0 (devel) (s20150603-96-g19009ec)
$ iverilog -Wall mp_proc.v
$ iverilog -Wall mp_proc.v -t sizer
mp_proc.v:8: warning: Process not synthesized.
mp_proc.v:8: warning: Process not synthesized.
mp_proc.v:8: warning: Process not synthesized.
ivl: t-dll.cc:1062: virtual void dll_target::logic(const NetLogic*): Assertion `nex->t_cookie()' failed.
Aborted

This example stripped down from working, tested production code.

---

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--
Steve Williams "The woods are lovely, dark and deep.
steve at icarus.com But I have promises to keep,
http://www.icarus.com and lines to code before I sleep,
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[Martin Whitaker]

Well, it turned out to be quite a bit harder than I thought, but this is now fixed in the master branch. This could be back-ported to v10, but I'll leave it to mature a bit first.