Xilinx Floating Point C Simulation aka VHDL/Verilog --> C Conversion?

Hi Guys,

I need a C Simulation of some Floating Point Cores from the Xilinx coregen. 
I thought about automatically converting the behavioral VHDL code to C, e.g. 
with V2C or VHDL-2-C (found via comp.lang.vhdl FAQ part 3).

While I'm investigating this -- has anyone in this group already done 
something similar, or are there C Simulations of the cores available 
somewhere?

Thanks,
Simon

Hi Simon,

"Simon Heinzle" <sheinzle@inf.ethz.ch> wrote in message
news:449fefd7$1@news1.ethz.ch...
> Hi Guys,
>
> I need a C Simulation of some Floating Point Cores from the Xilinx
coregen.

YHM.

At the risk of being deluged: if anyone else has a similar requirement, now
would be a good time to ask. Reply here or email me directly with details of
what you're looking for...

Cheers,

    -Ben-

Simon Heinzle wrote:
> I need a C Simulation of some Floating Point Cores from the Xilinx coregen.
> I thought about automatically converting the behavioral VHDL code to C, e.g.
> with V2C or VHDL-2-C (found via comp.lang.vhdl FAQ part 3).
>
> While I'm investigating this -- has anyone in this group already done
> something similar, or are there C Simulations of the cores available
> somewhere?

Hi Simon,

People simulate for two reasons ... to prove correctness, and to
evaluate timings and performance. The translation from HDL to C is
primarily simulation to verify correctness, especially where cores are
involved. Timing/performance simulation requires a very tight
integration with the target tool chain and architecture, something lost
with generic C simulation of an HDL source.

Just what are you looking for?

John

Can't you co-simulate? that is, put a SystemC/FLI/VHPI wrapper around your C 
code and load that into your simulator? Alternatively, use shared 
memory/files/sockets to communicate between your C code and your simulator.

If you do translate,  how are you planning to validate your translated 
model? Remember you are converting from a concurrent to a sequential 
language which might not be that easy...,

Hans
www.ht-lab.com



"Simon Heinzle" <sheinzle@inf.ethz.ch> wrote in message 
news:449fefd7$1@news1.ethz.ch...
> Hi Guys,
>
> I need a C Simulation of some Floating Point Cores from the Xilinx 
> coregen. I thought about automatically converting the behavioral VHDL code 
> to C, e.g. with V2C or VHDL-2-C (found via comp.lang.vhdl FAQ part 3).
>
> While I'm investigating this -- has anyone in this group already done 
> something similar, or are there C Simulations of the cores available 
> somewhere?
>
> Thanks,
> Simon
>
> 

fpga_toys@yahoo.com wrote:

: People simulate for two reasons ... to prove correctness, and to
: evaluate timings and performance. The translation from HDL to C is
: primarily simulation to verify correctness, especially where cores are
: involved. Timing/performance simulation requires a very tight
: integration with the target tool chain and architecture, something lost
: with generic C simulation of an HDL source.

: Just what are you looking for?

I can think of a few things...

For example you might want to create a model in C / Matlab / whatever of a 
wider system incorporating an FPGA pipeline and feed it lots of sample 
datasets or link it to a Monte-Carlo simulation etc., and look at the 
effect of precision/dynamic range in the context of the overall system.

A quick and dirty way of doing that is to do some bit masking etc. in C.

---

cds

Hi John and cds,

> People simulate for two reasons ... to prove correctness, and to
> evaluate timings and performance. The translation from HDL to C is
> primarily simulation to verify correctness, especially where cores are
> involved. Timing/performance simulation requires a very tight
> integration with the target tool chain and architecture, something lost
> with generic C simulation of an HDL source.

We have an arithmetic C model with standard IEEE single precision floats. 
However, in our FPGA implementation we use several different (custom) 
floating point formats, mainly due to the limited resources.

The C model is used to generate stimuli vectors for the HDL simulation. 
Surely we play tricks to quantize the intermediate results of the single 
precision operations, but the results often differ (in a few bits) from the 
HDL simulation, which is quite annoying (and not practical for automated 
testing).

In short: I'm just looking for a bit-accurate (non cycle-accurate) model of 
the Floating Point Operators from Xilinx.

Thanks,

Simon

Hi Hans,

also see my other post.

> Can't you co-simulate? that is, put a SystemC/FLI/VHPI wrapper around your 
> C code and load that into your simulator? Alternatively, use shared 
> memory/files/sockets to communicate between your C code and your 
> simulator.

I need floating point operators which produce the same result as the Xilinx 
FP Cores (bit-accurate, not cycle accurate). Shared memory/files/sockets 
sound like a lot of work.

> If you do translate,  how are you planning to validate your translated 
> model? Remember you are converting from a concurrent to a sequential 
> language which might not be that easy...,

I think the Xilinx Cores don't include feedback paths, only a forward 
pipeline. This should not be so difficult to translate. Validation could be 
done by applying the same stimuli to a HDL and the C Simulation and 
comparing the outputs.

Thanks,
Simon 

Simon Heinzle (sheinzle@inf.ethz.ch) wrote:
: Hi John and cds,

: We have an arithmetic C model with standard IEEE single precision floats. 
: However, in our FPGA implementation we use several different (custom) 
: floating point formats, mainly due to the limited resources.

: The C model is used to generate stimuli vectors for the HDL simulation. 
: Surely we play tricks to quantize the intermediate results of the single 
: precision operations, but the results often differ (in a few bits) from the 
: HDL simulation, which is quite annoying (and not practical for automated 
: testing).

: In short: I'm just looking for a bit-accurate (non cycle-accurate) model of 
: the Floating Point Operators from Xilinx.

I'll second that request in light of Ben Jones' posting.

Simon, I don't know if you are aware of GHDL?  It's a VHDL front end for 
GCC which spits out object files, so you may be able to compile the Xilinx 
Behavioural model into a form you can link C code against...

What sort of performance would you be happy with compared to machine 
native floats?

Cheers,
	Chris

Hi Chris,

> I'll second that request in light of Ben Jones' posting.

Dito, I really hope Xilinx will develop the C models.

> Simon, I don't know if you are aware of GHDL?  It's a VHDL front end for
> GCC which spits out object files, so you may be able to compile the Xilinx
> Behavioural model into a form you can link C code against...

Thanks! I'll definitely have a look at that one.

> What sort of performance would you be happy with compared to machine
> native floats?

Hmm, doesn't need to be very fast, but it should be faster than the HDL 
simulation. Compared to native floats, I think there will be a huge 
performance drop (~10 to 100 times slower) when doing it bit-accurate.

Best,
Simon