Re: [sv-cc] New Mantis item (274) on DPI's svBitVec32 --> open arrays 27.1.2

> Please check in the "Description" field of this Mantis item.
> In there I explicitly state that the directly-C-compatible
> small value types (longint, int, shortint, and byte) are still
> to be passed by value rather than by svBitPackedArrRef.

Doug,

Types 'int' and 'signed bit[31:0]' seem to be semantically equivalent
and thus mutually exchangable. Yet the former is to be passed by value and
the later by reference? Or I'm missing something?

Consider this:

import "DPI" foo = function foo1(int i);
import "DPI" foo = function foo2(signed bit[31:0] i);

I suppose that the above definitions are correct since both function headers
are equivalent. Both refer to the very same function foo, so both should
pass their argument using the same passing mode.

Thanks,
Andrzej

> I totally agree with you that it's vital to continue to do so.
>
> The case I'm talking about here is for non-C-compatible type
> of dimensioned, packed bit arrays "bit [y:x]".
>
> Regards,
> Doug
>
> > -----Original Message-----
> > From: Andrzej I. Litwiniuk [mailto:Andrzej.Litwiniuk@synopsys.com]=20
> > Sent: Wednesday, October 27, 2004 7:18 AM
> > To: Warmke, Doug
> > Cc: sv-cc@eda.org
> > Subject: Re: [sv-cc] New Mantis item (274) on DPI's=20
> > svBitVec32 --> open arrays 27.1.2
> >=20
> > > We discovered another minor difficulty in DPI.
> > > The crux of the matter involves the "small" packed 2-state type
> > > modeled with svBitVec32. When a 2-state vector is <=3D 32 bits,
> > > it is no longer passed by reference, but rather by value.
> > > This makes it impossible for a DPI user to create a single
> > > imported function that accepts an arbitrary width 2-state
> > > vector as an argument.
> >=20
> > Doug,
> >=20
> > I believe that open arrays were intended exactly for what you=20
> > want to achieve,=20
> > i.e. to "make it possible for a DPI user to create a single=20
> > imported function=20
> > that accepts an arbitrary width 2-state vector as an argument."
> >=20
> > LRM 27.1.2: "Formal arguments of an imported function can be=20
> > specified as open arrays.=20
> > A formal argument is an open array when a range of one or=20
> > more of its dimensions, packed=20
> > or unpacked, is unspecified. [...] An actual argument shall=20
> > match the formal one regardless=20
> > of the range(s) for its cor-responding dimension(s), which=20
> > facilitates writing generalized=20
> > code that can handle SystemVerilog arrays of different sizes."
> >=20
> > So in my opinion we have both; generality and efficiency for=20
> > "typical" cases.
> > Pls. also note, that passing small values 'by value' rather=20
> > than by a reference is consistent=20
> > with C. If small values, like int, were not passed by value,=20
> > then it will be impossible=20
> > to call standard C library functions from SV.
> >=20
> >=20
> > Thanks,
> > Andrzej
> >=20
> >=20
> > > Details are located at
> > > http://www.eda.org/svdb/bug_view_page.php?bug_id=3D0000274
> > >=20
> > > Charles,
> > >=20
> > > Can you please assign me to be the owner of this item?
> > > I will upload a proposal that basically simplifies DPI by
> > > eliminating the exception for bit vectors <=3D 32 bits in width.
> > >=20
> > > Thanks and regards,
> > > Doug
> > >=20
> > >=20
> >=20
> >=20
>
Received on Wed Oct 27 08:37:21 2004