Subject: Re: [sv-cc] Perspectives from a "user" of the SV DPI C-layer
From: Andrzej Litwiniuk (Andrzej.Litwiniuk@synopsys.com)
Date: Tue Apr 01 2003 - 11:12:41 PST
> I've tried to put on the hat of a user of the DPI C-layer
> use model and have come up with some possibly interesting
> perpectives.
>
> In the C-layer we've created two categories of applications
> in terms of compatibility across environments:
>
> 1. Binary compatible - those that only require svdpi.h
> 2. Source compatible - those that also require svdpi_src.h
>
> After attempting to use the interface, I'm beginning to
> think there will be a widely used 3rd model of compatiblity:
>
> 3. Binary compatible across all environments that chose
> to use svBitVec32[] as the implementation type for
> svBitPackedArrRef.
John,
I'm not surprised at all.
In section A.3, last paragraph, we wrote:
"The values of SystemVerilog packed types can be accessed [...] or directly
through pointers using the implementation representation. [...] The latter
[mode] allows for tool-specific, performance-oriented tuning of an application,
though it also requires recompiling with the implementation-dependent
definitions provided by the vendor and shipped with the simulator."
> It is my feeling that many implementors will choose svBitVec32[]
> as the implementation type and user of those products will
> benefit from the cleaner, simpler use model offered by #3 above.
Implementors may as well want to take advantage of 64-bit hardware
and use svBitVec64[] where suitable (or depending on the platform), or - I'm speculating - use less memory cosuming representation where possible, something
like svBitVec8[], svBitVec16[], or svBitVec128[] in order to take advantage of
loads/stores for quadwords.
That's why it is smart not to bind them.
With canonical representation and no specific representation required
we can have it both ways.
Regards,
Andrzej
> I'm not suggesting that we change our spec - let's just be aware
> that there may be a "de-facto" compatibility model that a set of
> vendors may choose just in the interest of making things easier
> for their users.
>
> -- johnS
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