RE: [sv-ec] use model for non-blocking event triggers

Also, the nonblocking event trigger was added early in the development of
SystemVerilog, before program blocks and new event scheduling regions were
added.  The later constructs remove much of the need for a nonblocking event
trigger, but it is still useful for verification that for whatever reason
does not use program blocks.

Stu
~~~~~~~~~~~~~~~~~~~~~~~~~
Stuart Sutherland
stuart@sutherland-hdl.com
+1-503-692-0898
  

> -----Original Message-----
> From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On 
> Behalf Of Steven Sharp
> Sent: Monday, February 27, 2006 11:21 AM
> To: sv-ec@eda.org; michael.burns@freescale.com
> Subject: Re: [sv-ec] use model for non-blocking event triggers
> 
> Since nobody else has responded, I'll take a stab:
> 
> I don't know that they were added for any particular use-model, or
> for any interaction with SystemVerilog constructs.  They were added
> for completeness and consistency within Verilog.  An event is like
> a variable that has no data value, just the abstract concept of a
> "value change".  Since variables can have their values changed with
> blocking or nonblocking assignments, it also makes sense to be able
> to create this abstract "value change" on an event using either
> blocking or nonblocking semantics.  Otherwise, you might have the
> bother of creating a 1-bit variable, initializing it, and toggling
> it, because you wanted nonblocking semantics and there was no way
> to do this with a named event.
> 
> One possible reason for this would be to avoid race conditions where
> one process triggers the event before another starts waiting on it.
> This is similar to the reason why the "triggered" property was added
> to named events, but is a more Verilog-like solution.  It 
> also provides
> a finer degree of control than the "triggered" property.  Once the
> "triggered" property is set, it stays set until simulation time
> advances.  There is no way to use it to signal back and forth multiple
> times in zero-delay.  The nonblocking event trigger could do so.
> 
> Steven Sharp
> sharp@cadence.com
> 
>