DirectC vote

Subject: DirectC vote
From: Michael Rohleder (michael.rohleder@motorola.com)
Date: Mon Sep 30 2002 - 08:59:02 PDT

Hello Yatin,

below is my input on the DirectC interface donation from Synopsys.

Short feedback the interface:
 - I very much like the clear and simple way of interfacing to C/C++
 - I also like that each function has a clearly defined scope of objects it can affect;
    this helps in optimizations and I expect some major performance improvements here.
 - the overall interface methodology is a good step in the right direction
BUT
 - Having abstract access and direct access exhibited to an user is a big failure
 - we need to make sure there is a 1:1 relationship between data types provided in SystemVerilog and the data types defined for DirectC; otherwise this interface is useless
 - I have some doubts that the functionality of DirectC (on its own) is sufficient for its stated purpose (e.g. permit to integrate a system consisting of multiple C/C++ into a Verilog simulation)
 - cmodules are an interesting concept, but I am not sure whether this method is not too specific for a compiled simulator like VCS (just from a gut feeling). I like the overall methodology, but I am unsure whether it might not be too specific or too
stringent. But, as said this is something that needs to be evaluated in more depth.
 - there seems to be some inconsistencies between the usual SystemVerilog language nomenclature (this needs some more elaboration, I think)
 - I have some concerns about how to use DirectC (it looks like you always have to start with the SystemVerilog side); but I am not sure whether this is imposed by the standard. Very like I just misunderstood the standard ...
 - Last but not least we need to clearly define the intended relationship to PLI and VPI (is it forbidden or permitted to run related functions within a DirectC code; I think it is essential to define this UPFRONT -- don't care is the wrong statement)

As everybody sees, I am having some problems and concerns with the DirectC interface. On the other side, I think it would be a very valuable starting point for defining an interface. Starting from here is for sure much, much better than doing everything
from the scratch. Within our team in Motorola we have three possible results of a review: accepted, conditionally accepted, denied.
DirectC is clearly a candidate for the second.

As such my vote is YES to accept DirectC as the basis for the work to define an interface, but it would be clearly NO, if someone would ask me to accept it as is. There is a good deal of work that needs to be done to make it an excellent and easy to use /
easy to understand interface.

Just my $0.02.

-Michael 

--
Quote of the day:
"Better to remain silent and be thought a fool than to speak out and remove all doubt."
[Abraham Lincoln (1809-1865)]

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