FPGA C Compiler on sourceforge.net (TMCC derivative)

Eric Smith wrote:
> That doesn't explain *why* it's an excellent alternative.  I can just
> as easily state that "C provides a terrible alternative to VHDL/Verilog
> for algorithmic expression of tasks targetting FPGAs for reconfigurable
> computing".  So why is their statement any more accurate than mine?

There are probably a few hundred billion statements of C/C++ IP for
designs which
contain easily reusable code segments (IE cores) in nearly every
application
area. Probably a few trillion, when you include privately held IP in
addition
to what is on SourceForge and other open source depositories.

I suspect, the total IP coded in VHDL/Verilog is three to four orders
of magnitude less.

So that is three reasons why C can be an excellent althernative for
reconfigurable computing projects, and for the home hobbyist that
already knows C and would like to use an FPGA for a reconfigurable
platform for their robotic or other project.

air_bits@yahoo.com wrote:
> Eric Smith wrote:
> 
>>That doesn't explain *why* it's an excellent alternative.  I can just
>>as easily state that "C provides a terrible alternative to VHDL/Verilog
>>for algorithmic expression of tasks targetting FPGAs for reconfigurable
>>computing".  So why is their statement any more accurate than mine?
> 
> 
> There are probably a few hundred billion statements of C/C++ IP for
> designs which
> contain easily reusable code segments (IE cores) in nearly every
> application
> area. Probably a few trillion, when you include privately held IP in
> addition
> to what is on SourceForge and other open source depositories.
> 
> I suspect, the total IP coded in VHDL/Verilog is three to four orders
> of magnitude less.
> 
> So that is three reasons why C can be an excellent althernative for
> reconfigurable computing projects, and for the home hobbyist that
> already knows C and would like to use an FPGA for a reconfigurable
> platform for their robotic or other project.

  How about some examples, of some real applications, that can be coded
in either, and the resulting source examples, and the FPGA resource
mapping that results ?

  I presume a mixed-language design is possible ? - an example of that
as well, would assist understanding.

  Otherwise, it's all arm-waving.....

-jg

Eric Smith wrote:
> I'm not the one claiming that any particular HDL is better than
> another.  But I'm trying to understand the hype about using C as
> an HDL.  Where is the actual benefit?

You have it backwards. The intent is not to use C for hardware design,
but to use FPGA's for computing. There is a grey area in between, but
the view point is from completely different ends of the problem design
space.

Jim Granville wrote:
>   How about some examples, of some real applications, that can be coded
> in either, and the resulting source examples, and the FPGA resource
> mapping that results ?
>
>   I presume a mixed-language design is possible ? - an example of that
> as well, would assist understanding.
>
>   Otherwise, it's all arm-waving.....

Most applications of reconfigurable computing are not hardware design
applications, so any pure HDL may be the wrong tool, as it's design
focus
is at the gate/register level.

Reconfigurable computing is about taking tranditional C/C++
applications and pushing the resource intensive parts into net lists
for a performance gain ... frequenly as much as 200 times the fastest
RISC/CISC processors by removing memory latency and ALU pipelines (both
of which are serial resources) from the critical path.

Moving the front end of web servers, router/classifier logic and TCP/IP
stacks into several large FPGA's ... VertexII-Pro's with rocket IO's
and PPC backend engines is one example. These applications are already
written in C, and get married to the external hardware with logic
typically written in VHD/Verilog.

Likewise, most protocol converters which interface different fibre
connections are freqently being pushed into fpga's to maintain wire
speed operation.

Mixed C, VHDL, Verilog, and schematic are all very likely. C is just
one
more implementation tool.

air_bits@yahoo.com writes:
> There are a few hundred thousand engineers on the planet that can
> express large complex algorithms in C, and a few tens of thousands of
> engineers that can express large complex algorithms in VHDL/Verilog,

Of those few hundred thousand that know C, very few have any clue how
to design hardware.  If you turn them loose with C as an HDL, you're
going to end up with really crappy hardware, just like when programmers
are thrust into Verilog or VHDL.

It's not knowledge of the syntax of a particular language that's the
problem.  The semantics of hardware design are fundamentally different
from the semantics of sequential software design.

> and probably a few thousand that can actually grasp the test vector
> space and simulation effort necessary to actually get a large
> VHDL/Verilog design working for large complex alogoritsms.

Are you claiming that test vectors and simulation aren't needeed when
using C as an HDL?  I'd be very skeptical of any such assertion.

> The embedded logic analyzer cores are a very poor subsitute when
> debugging complex algorithms with lots of state and data.

What's that got to do with your choice of HDL?  If you want to know
what's going on inside your FPGA, that's not fundamentally any easier
with C as your HDL than it is with Verilog or VHDL.

Eric

air_bits@yahoo.com writes:
> You have it backwards. The intent is not to use C for hardware design,
> but to use FPGA's for computing. There is a grey area in between, but
> the view point is from completely different ends of the problem design
> space.

You're right, I wasn't aware of that distinction.

Still, if you're going to use reconfigurable computing, surely each
configuration is a hardware design, and much better expressed in a
language optimized for hardware design, rather than a language optimized
for strictly sequential operation.

Eric

air_bits@yahoo.com wrote:

> Rene Tschaggelar wrote:
> 
>>Why are those guys so keen on C ? Suggesting
>>compatibility with something while having least
>>readability ?
>>
>>Rene
> 
> 
> The description at the project page pretty much says it all:
> 
> "C provides an excellent alternative to VHDL/Verilog for algorithmic
> expression of tasks targeting FPGAs for reconfigurable computing."
> 
> Project page at http://sourceforge.net/projects/fpga
> 
> The object is to use FPGAs as computing engines, and less concerned
> about how to describe circuits in an HDL for synthesis, as most
> hardware designers would with VHDL or Verilog. VHDL and Verilog are the
> rough equivalent of programming in assemenbly language, as the
> implementation languages are directly expressing clocks, registers and
> wires which adds a tremendous design state factor and skill level in
> their use.
> 
> Simplifed C to netlist compilers, such as FpgaC are attempting to hide
> most of synthesis details, to ease the design burden for hardware
> implementations of applications which have rich algorithmic complexity.
> These applications range from doing network stacks in FPGAs for wire
> speed performance at gigabit rates, to richly parallel algorithms such
> as searching which are performance limited by the serial nature of
> traditional CPU/Memory architectures.
> 
> FPGAs in this decade are simply building blocks for high performance
> computing,
> not just a dense PLD to express hardware funtions for the logic
> designer.

Thanks. It is a pitty that C was chosen. The choice
of C means some guys want to adhere to a standard,
instead of flexibly adapt to the problems ahead.
There should be a way to tell the compiler how
quick I want to have an operation. Do I want a one
cycle result with an enormous loockup table, do I
want an N-digit multiply accumulate loop, do I
want an NlogN solution or is it even less important.
Is this being solved by a bunch of #pragma ?

I'd be interested in the first floating point unit
coming out of such a compiler.

Rene

HDL has a benefit that you can include abstract ideas in your FPGA.  That's
why HDL is better.

I can also see the point of using C as a base language... But I can just
imagine the latest windows.. instead of crashing once a week..it now crashes
every mili second :-).. Poor software is still poor software... C isn't
typed strong enough to use with out  adding other tools, so it would be at
the bottom of my list of recommended software.  Also anything you create in
C you will need to be able to verify.  Failing to do so will only lead to
hours and hair loss.

Pascal would have been a better choice IMO.

Simon


"Eric Smith" <eric@brouhaha.com> wrote in message
news:qhfyqelkvf.fsf@ruckus.brouhaha.com...
> air_bits@yahoo.com writes:
> > I can build them at a schematic level too, so why is any HDL better?
> > I can even wire them out of TTL so why is using an FPGA better?
> > Heck, I can even wire them out of diodes or vacumn tubes, ....
> >
> > So why waste people time bitching about others preferences, and the
> > tools
> > they use to implement them. If you like VHDL, certainly use it.
>
> I'm not the one claiming that any particular HDL is better than
> another.  But I'm trying to understand the hype about using C as
> an HDL.  Where is the actual benefit?
>

Simon Peacock wrote:
> HDL has a benefit that you can include abstract ideas in your FPGA.  That's
> why HDL is better.
> 
> I can also see the point of using C as a base language... But I can just
> imagine the latest windows.. instead of crashing once a week..it now crashes
> every mili second :-).. Poor software is still poor software... C isn't
> typed strong enough to use with out  adding other tools, so it would be at
> the bottom of my list of recommended software.  Also anything you create in
> C you will need to be able to verify.  Failing to do so will only lead to
> hours and hair loss.
> 
> Pascal would have been a better choice IMO.

Or Modula-2, or IEC 61131, ... or even better, something like :


http://research.microsoft.com/fse/asml/
"AsmL is the Abstract State Machine Language. It is an executable 
specification language based on the theory of Abstract State Machines."

-jg

Rene Tschaggelar (none@none.net) wrote:

: Why are those guys so keen on C ? Suggesting
: compatibility with something while having least
: readability ?

: Rene

Oee might ask the same question about hardware engineers and 
Perl - why is this such a commonly used tool?  I'd venture to
guess that after being forced to accept VHDL or Verliog as the
prime language, the idea of using Perl or C derivatives for 
hardware proramming doesn't seem so twisted.

cds