Subject: Re: [Fwd: [sv-bc] Removal of the SystemVerilog logic data type]
From: Stefen Boyd (stefen@boyd.com)
Date: Fri Jan 24 2003 - 16:07:36 PST
At 03:23 PM 1/24/2003 -0800, Stuart Sutherland wrote:
>Perhaps calling logic a "universal" data type is too general, but keep in
>mind that SV 3.0 makes logic the default type for most
>circumstances. That makes it pretty close to universal, if not completely
>universal. In fact, in the few places that SV 3.0 says the default data
>type is something other than logic, I have noticed the SystemSim Superlog
>simulator still defaults to logic, further proving the potential of logic
>being a universal data type. The last-write-wins behavior for wired
>outputs may not be the best representation of hardware, but syntactically,
>logic can truly be used almost universally.
If we do move to using var to get the shared variable behavior
in 3.1 versus the shared behavior we got by default for all the
new types added in 3.0, the possibility of logic as a truely
"universal" data type is reopened.
The strongest argument that killed my universal type proposal
for logic was that all the new types allowed shared variable
behavior, so making an exception for logic would be a strange
exception.
What I had proposed for logic was:
1) Allow it to be driven by procedural blocks (i.e. always, initial)
*or* drivers (i.e. cont assigns, module inst outputs, gate outputs)
2) If both procedural assignment and driver, then error (nothing new
so far)
3) If there are multiple drivers, use net resolution (treat it like a
wire)
If the bc decides to use explicitly shared variable behavior using
var instead of the 3.0 implicitly shared variable behavior, I would
love to see the reconsideration of having a logic type that could
morph itself into a truly universal type. That would make the retention
of this keyword worthwhile. Otherwise reg and logic are almost
identical (assuming *explicit* shared variable behavior).
Eliminating logic by allowing reg to take on ability to be used
with a single driving statement (such as cont assign) would be ok,
but retaining logic and making it truly universal would be extreemly
valuable (but this would seem to hinge on the BC going to explicitly
shared variables).
Stefen
--------------------
Stefen Boyd Boyd Technology, Inc.
stefen@BoydTechInc.com (408)739-BOYD
www.BoydTechInc.com (408)739-1402 (fax)
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