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Old 05-14-2009, 06:34 AM
Andreas Ehliar
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Default Re: XML for LUT+FF netlist representation in (academic) tools

On 2009-05-14, acd <[email protected]> wrote:
> I think this second step should be easily doable with XSLT if the
> netlist is represented as XML.
> I wonder if there are existing formats and tools to do this.


I would look at the kind of formats that commercial synthesis tools
output. This is most likely going to be some sort of EDIF based format.
I know that Precision outputs EDIF files when synthesizing to Xilinx and
I guess that other vendors' backend tools can handle EDIF inputs as well.

Another choice if you are targetting Xilinx is XDL, although that is
a bit more low level (you will have to map LUTs into slices before you
can use XDL).

/Andreas
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Old 05-14-2009, 08:14 AM
acd
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Default XML for LUT+FF netlist representation in (academic) tools

Hi,

I am currently working on a circuit generator problem, which I also
want to target to FPGAs.
However, I want to make my tools somewhat technology/vendor
independent by generating a netlist of LUT's and
FlipFlops. This means my tool would be configured with the available
LUT sizes and area costs.
A second step should then translate the netlist into a technology-
specific form.
I think this second step should be easily doable with XSLT if the
netlist is represented as XML.
I wonder if there are existing formats and tools to do this.
I have found individual academic projects that do something similar,
but none seemed to have reached a wider scope.
Is there a wide-spread approach?

Currently I target ASIC technologies and generate VHDL.
If I give this VHDL for instance to ISE, it runs for hours and I am
not convinced that the result is close to what I intend.
The reason is that this VHDL shares signals on a gate level. So the
FPGA mapper has a hard time to figure out which gates need to be
replicated and put together with other gates into a LUT.

Regards,
Andreas

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Old 05-14-2009, 10:42 AM
Brian Drummond
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Default Re: XML for LUT+FF netlist representation in (academic) tools

On Wed, 13 May 2009 23:14:41 -0700 (PDT), acd <[email protected]> wrote:

>Hi,
>
>I am currently working on a circuit generator problem, which I also
>want to target to FPGAs.
>However, I want to make my tools somewhat technology/vendor
>independent by generating a netlist of LUT's and
>FlipFlops. This means my tool would be configured with the available
>LUT sizes and area costs.
>A second step should then translate the netlist into a technology-
>specific form.

....

>Currently I target ASIC technologies and generate VHDL.
>If I give this VHDL for instance to ISE, it runs for hours and I am
>not convinced that the result is close to what I intend.
>The reason is that this VHDL shares signals on a gate level. So the
>FPGA mapper has a hard time to figure out which gates need to be
>replicated and put together with other gates into a LUT.


It sounds as if your tool has a good idea what to replicate and how to optimally
map it.

You could consider adding this information to the VHDL in the form of attributes
- e.g. "keep" and "RLOC" when targetting Xilinx; others for other technologies;
probably at the second tech-specific stage. Search online for "Death of the
RLOC?" to see this in action.

Be prepared for a tussle with ISE to overcome its optimisations...

- Brian
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