Subject: Re: [sv-cc] Polls on extern/export and representation of SV data types
From: Michael Rohleder (michael.rohleder@motorola.com)
Date: Tue Mar 11 2003 - 09:12:38 PST
IMHO I would not have this problem, but I might be missing one of your important points here. I will describe this in my response to John
S.'s email, since there is some overlap. There is anyway a lot of email noise here.
-Michael
Joao Geada wrote:
> Michael,
>
> with respect to top-level externs: how would you solve this issue if you were
> not using DPI; ie if you were limited to just SystemVerilog ?
>
> Joao
> ==============================================================================
> Joao Geada, PhD Principal Engineer Verif Tech Group
> Synopsys, Inc TEL: (508) 263-8083
> 344 Simarano Drive, Suite 300, FAX: (508) 263-8069
> Marlboro, MA 01752, USA
> ==============================================================================
>
> -----Original Message-----
> From: Michael Rohleder [mailto:michael.rohleder@motorola.com]
> Sent: Tuesday, March 11, 2003 5:25 AM
> To: Joao.Geada@synopsys.COM
> Cc: sv-cc
> Subject: Re: [sv-cc] Polls on extern/export and representation of SV
> data types
>
> Joao,
> thanks a lot. Comments interspersed. Hope this clarifies my problems a little bit. Kevin might have some more or even better examples.
>
> -Michael
>
> Joao Geada wrote:
>
> > Michael,
> >
> > With respect to externs at top-level, the rules are no different than those
> > that apply to any other SV declaration: you cannot declare the same name
> > twice. Given that SV supports conditional compilation etc, I do not see a
> > compelling reason to violate basic SV rules just for DPI.
> > Of course, I am willing to change this if some can give a convincing reason as
> > to why DPI must have this flexibility.
>
> I agree to your point about compliance with other SV declarations, but I have to say that this is a restriction that I envision as being
> extremely reuse unfriendly. See the following example (currently from hot air, but I have seen sthg. similar already in other contexts):
>
> - Assume you have a company internal bus standard, and there are some C functions used by the related code. So you might have a
> testbench or protocol converter that uses some C code (e.g. for signature calculation, ECC calculation or similar) you have to declare
> as being external.
> - Of course your system need to include multiple instances of this bus/protocol
> - Now assume you have multiple groups providing you one or multiple blocks, all of them are using one instance of this bus
> - You are the poor integrator having to integrate all these blocks
> - Think about a system consisting of about 100 blocks from 7 groups located on 4 continents. I have seen this more than once!
>
> When for whatever reason more than one of these groups or you have decided to locate the blocks in the top-level, you might experience a
> massive amount of error messages due to multiple extern declarations, when the extern declarations are being done outside of other
> blocks. This is also the case when all these extern declarations are exactly matching.
>
> The only way to avoid this is to change the hierarchy of your system (I am sure you don't want to suggest this to a designer) or to
> introduce additional hierarchies, just to avoid those errors. On the other side this is something you very likely want to avoid.
> Everybody within your company should (re-)use the internal standard, which uses these external C functions. As such the bus/protocol
> block is very likely a standalone block that is located near to the top level. It will be only instantiated once (this can be of course
> controlled), but what about the extern declarations usually being done by the other blocks. Do you want to modify the source code 100
> blocks? Some of them you might simply not have write access to ...
>
> IMHO, the proposal is unbalanced here from a usage point of view:
> - everything is O.K. when you bury the extern definitions within lower hierarchy levels
> - as soon as you have a more flat hierachy or you want to reuse blocks containing C code on the top level or you want to define stuff
> at the top level you have to be very carefully not to collide with somebody else's code
>
> This is my problem.
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