[myhdl-list] Re: Cosimulation with the simple FSM example.

[Jan D. <ja...@ja...>]

Brendan Rankin wrote:
> I'm having some issues getting cosimulation to work with the simple FSM example
> an d Icarus.  I have two issues:
> 
> 1.  I'm seeing an 'x' being assigned to the state value, at some point.
>     - I can get around this by removing the $finish from the casez statement in
> the generated Verilog.
>     - I suspect that this issue is due to the active-inactive transition of
> reset_n.  If so, then it's not an issue at all.

It's not clear to me what's happening. It would be useful to see the
exact code you're using, including the testbench.

> 2.  It appears that the enum'ed state types are not being properly de-enum'ed. 
> I get the following traceback:

> I can work around this, as well, by simply changing this exception to a print
> statement, but it would be nice to have a "fix" for this one.  It does appear
> that I'm seeing the values of SEARCH, CONFIRM, SYNC...but these are not being
> converted to the expected type _enum.

Enum is a high-level type with no direct equivalent in Verilog. So the
Verilog convertor maps enum items to encoded values. So there is some
information loss.

Co-simulation has no idea that the Verilog you co-simulate came from a
MyHDL conversion, or that you wrote it by hand. So it cannot
automatically map the encodings back to the high-level type -
you have to do that explicitly (by a map from encodings to
enum items, in the MyHDL domain).

Thinking about it, I guess that the Enum type should offer some
help to make this easier, that is, offer some kind of an interface
to retrieve an enum item based on its encoding. But currently
it doesn't.

> Unless I'm doing something terribly wrong, you should be able to duplicate this
> by simply trying to cosimulate the FSM example with Icarus.

Please consider posting the code you're using. It always saves time
when troubleshooting.

Best regards,

Jan

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