Subject: RE: Proposal: Deprecate procedural assign-deassign
From: David Smith (david_smith@avanticorp.com)
Date: Mon Oct 29 2001 - 10:50:13 PST
So, what is the voting process? I agree by the way as well.
David
-----Original Message-----
From: John Sanguinetti [mailto:jws@forteds.com]
Sent: Monday, October 22, 2001 1:04 PM
To: vlog-pp@eda.org
Subject: Re: Proposal: Deprecate procedural assign-deassign
Again, I agree.
At 8:42 AM -0700 10/22/01, Clifford E. Cummings wrote:
>Deprecate procedural assign-deassign
>
>I don't know the formal wording but I propose that we vote to
>deprecate procedural assign-deassign statements. Some of the most
>gosh-awful models have been written with these infinitely abusable
>statements that at first glance appear to be similar to a continuous
>assignment statement.
>
>I think every new Verilog user at some time has placed an assign
>statement inside of an always block where no assign statement was
>required and either got lucky on the behavior or confused.
>
>The concept of taking control of a variable with a procedural assign
>statement that updates the LHS anytime the RHS variable changes,
>even if the RHS variable is not in the sensitivity list is pretty
>strange. The concept that last assign wins is also confusing and
>restoring other non-assign procedural assignments to activity after
>a deassign statement is similarly confusing. I have worked with
>customers that had to translate their old assign-deassign Cadence
>Synergy code into synthesizable code for Synopsys and Synplicity
>with multiple assign statements spread throughout a large model.
>Ultimately, I could not figure out what the assign priorities were
>within the code.
>
>The force-release commands do the same thing but they are rarely
>abused, not synthesizable by any tool, and rather clearly documented
>to be mostly for debugging purposes.
>
>Having both assign-deassign and force-release where the latter has
>higher priority and can also assign to wire types has always been
>confusing to new users.
>
>I would like to see this committee take a stand for sanity and
>deprecate procedural assign-deassign.
>
>Regards - Cliff
>
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