RE: [sv-bc] enumerated variable used with an equality operator

I see a lot of SV RTL code that uses enums and not just in FSMs.

Shalom


> -----Original Message-----
> From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org] On Behalf Of
> Greg Jaxon
> Sent: Friday, March 21, 2014 22:24
> To: Steven Sharp; SV_BC List
> Subject: Re: [sv-bc] enumerated variable used with an equality operator
> 
> We've certainly seen FSMs written with enum-valued states.
> I don't know whether they're "trending" or not.
> But the 'X initialization aspect does not directly affect synthesis.
> It's a matter of concern to simulators, if they are going to
> track how the first valid state of the machine emerges.
> 
> We don't synthesize implicit initializations at time 0.
> Instead we (try to) statically detect uses of uninitialized nets.
> Type-safety of enums opens up the possibility of optimizations that re-
> encode the enum state values.
> Some of this is old practice, and some is still blue-sky.
> So far the SV language hasn't unlocked any new opportunities here.
> 
> On 3/21/2014 2:59 PM, Steven Sharp wrote:
> > Your mention of synthesis makes me curious.
> >
> > One of the reasons for the "schizophrenia" that Gord mentioned is
> that
> > there are at least two different general uses for enums, which may
> have
> > different requirements.  There is the software-like use in
> testbenches,
> > where strong typing is more likely to be desired.  And there is the
> > hardware-like use in designs, for things like state machine states,
> where
> > overly strong typing is inconvenient.
> >
> > I originally assumed that the hardware-like uses would be common.  I
> > proposed the initialization of 4-state enums to X for this reason,
> because
> > initializing state machine states to known values would not correctly
> > model hardware initialization.  This could have led to faulty
> hardware.
> > But when I saw very little of this in user designs, I started
> thinking
> > that I had been wrong about this.
> >
> > Now I am curious whether you have started seeing more enums used in
> > synthesizable code.  Were they just slower to be adopted by users in
> > synthesizeable code (perhaps due to limited tool support as well as
> > conservativism), but are finally becoming more common?  Or are you
> just
> > speaking theoretically about what would be possible if users actually
> did
> > start using them this way?

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