The Cx programming language

by jclis • 12 years ago

106 47 12 years ago

eps• 12 years ago

In the example, shouldn't it be checking that stop bits are ones?

Does available() extract and discard the bit if one's available? Or does it act a flag that's reset upon reading? Why doesn't loop() extract stop bits then?

I mean, this is clearly aimed at a technical audience with embedded background, so the code should really match the specs, even if it's just an illustartive example :)

MootWoop13• 12 years ago

Hi I'm the person who wrote this example. In fact you don't need to check that stop bits are ones because one is the default: when nothing is being written on the line, it is high all the time. This is why it's just a matter of convention (number of stop bits) rather than a specific pattern.

EDIT: available checks that data is available on a port. If the test is true, then you can read from the port; if you don't read from the port, this is equivalent to an implicit read and data is discarded.

kw712• 12 years ago

Hi. I think this UART can be made better. A typical hardware UART receiver is clocked at a multiple of the signalling rate (16x is common) and the pin is sampled according to the clock. During the middle of the bit period, marks on the bus affect a counter whose value is compared to a constant, the result of which indicates whether the majority of samples indicate a mark or a space. The result of this goes into the receive shift register. The samples from the beginning and the end of the bit period are discarded.

This mechanism allows for timing differences between either end, and some immunity to electrical noise.

Also, sampling and validating the stop bit(s) will reveal framing errors.

niklasni1• 12 years ago

Hard to tell from the site if the language is proprietary or if it's just the IDE they're flogging.

I have to say "what this needs is another proprietary component in the toolchain" is not something I've ever thought when working with FPGAs. Quite the contrary.

MootWoop13• 12 years ago

Hi I'm a co-founder of Synflow and author of the website. Sorry if this is not clear about what is open source or not.

To answer your question the language, compiler, and IDE are open source: https://github.com/synflow/ngDesign We're using Xtext to develop the language. The open source version includes everything you need to design with Cx and then generate VHDL code. We also have a proprietary version that adds a Verilog code generator, exporters to third-party tools, and a C-based simulator.

I agree that a lot of tools for FPGAs are much too proprietary, hopefully we're contributing to changing that. I wish we could make it all open source but we also have to make a living :-)

runeks• 12 years ago

This looks pretty cool.

Would love to see a toy example of a double-SHA256 engine. Would be kind of cool if people could build their own Bitcoin mining ASIC, crowd fund it, and give everyone access to cheap Bitcoin mining ASICs.

MootWoop13• 12 years ago

Thanks!

You might be interested by my implementation of SHA-256 in Cx available on Github: https://github.com/synflow/sha-256 It is a toy example (I haven't implemented the pre-processing step), with an architecture that offers a good trade-off in terms of performance / area, so it's probably not the ideal implementation if you want a very highly-optimized ASIC, but it's still a good starting point.

bpg_92• 12 years ago

This needs to become a thing!!! I guess I will give Cx a chance.

MootWoop13• 12 years ago

We hope so too :) If somehow Cx doesn't live up to its promises and what you expect from it, please let us know! We're still improving it based on the feedback we get. Thanks!

scott_wilson464• 12 years ago

I can't help but feel that the VHDL that was written is a bit overly verbose. You could probably write something like:

  i_sm: process(clk, reset)
  begin
    if (reset) then
      state <= DATA_BITS;
    elsif (clk'event and clk = '1') then
      case (state)
        when DATA_BITS => 
          if (data_valid = '1') then
            if (count < 8) then
              count <= count + 1;
            else
              state <= STOP_BIT;
              count <= 0; 
            end if;
          end if;
        when STOP_BITS => 
          if (data_valid = '1') then
            if (count < num_stop_bits) then
              count <= count + 1;
            else
              state <= DATA_BITS;
              count <= 0;
            end if; 
          end if;
       end case
    end if;
  end process i_sm;

which is not too dis-similar from the Cx example (I've missed a few things out like port/signal declerations, just wanted to show the guts of the code). The thing I like about VHDL/Verilog is that its easy to tell the exact port names, what the clk is, the name and type of reset, etc which is useful information for putting the block in the context of an overall system.

nsiret5• 12 years ago

Hi Scott, I'm a co-founder of Synflow. You're right, the VHDL on our website is a bit overly verbose. I will update the website with the right version of the code that day.

And I also agree on your point. This is why we added properties to the language (http://cx-lang.org/documentation/properties) so one can either use the (implicit) default names and types for the clk, reset, etc. or explicit/tweek things for more complex systems.

scott_wilson464• 12 years ago

Actually another thing I am curious about is how asynchronous clock domains are handled Usually this is something thats quite tricky to model in a HLS tool. Also, how about simulating the interactions between the domains?

FraaJad• 12 years ago

That Ada roots doe.

csirac22• 12 years ago

It's been 10 years since I did much FPGA dev, but at the time I had a lot of fun in Celoxica Handel-C. Sadly I could never quite synthesize my project to the size I could achieve with Verilog. I seem to recall having the Virtex-II datasheets next to me when coding Verliog, not so much with the Handel-C so perhaps I never quite got the hang of driving the language optimally for the target device at hand...

My question is, to a layman like me - does Cx bring something to the table that other C-like HDLs missed?

Edit: I Also very much enjoyed a scheme-like HDL called confluence... Seems it fizzled out. Have any alternative HDLs stuck?

MootWoop13• 12 years ago

I think that the philosophy is different, and this implies a lot of things. We wanted to try something different, create a language and IDE that were easy to use rather than make something more or less compatible with C; and we aimed at making a language that could replace HDLs for most uses in the long term. This is why we created a new language from scratch rather than patching things up on top of C.

In practice, this means saner defaults (and better performance) than past C-like HDLs. Cx is cycle-accurate because this is how digital hardware works, and within a cycle you can have as many instructions as you want. There is no need for Handel-C's "par" statement, and it is much easier to understand and write code with good performance. In Cx, ports (Handel-C channels) can be "bare metal" so you can interact with the rest of the world, or slightly more sophisticated (with an additional synchronization signal). In general Cx is "fat free", what you type is what you get, so I'm pretty confident that logic consumption would remain under control :-) I've never written Handel-C, but from the manual it seems kind of complicated for even the simplest designs, and not very elegant.

I think most alternative HDLs have been abandoned :-/ Often the technology did not meet users' expectations: logic consumption was too high, and it was very difficult to obtain the desired performance. Additionally, I believe that these initiatives weren't targeted at the right public, and the target market itself was way too small. If you're interested, I've written a post about this on our blog: https://blog.synflow.com/marketing-disruptive-innovation/

csirac22• 12 years ago

Cool! I've actually had a Virtex-6 ML605 eval board for quite some time now, gathering dust... I always wondered what the Synflow toolchain looked like, it seems quite expensive - perhaps I can dust it off for Cx :-)

daphreak2• 12 years ago

I don't know if MyHDL(http://www.myhdl.org/) really stuck but I've used it a few times for some smaller things. What I really liked about it was how fast I could simulate while iterating on a design, and the fact that I could use Python unittest for testing.

I will definitely be taking Cx for a spin. Not wasting time with clock/reset/fsm boilerplate will make development faster. If I can get my hands on a trial of their cycle accurate simulator and can automate my test suites I'd be thrilled.

MootWoop13• 12 years ago

Yes it is still in use, and the simulation capabilities are quite advanced! It remains a HDL, better than VHDL and Verilog, so you still have to worry about resetting, clocks and state machine.

Just a word of caution the cycle accurate simulator is still a bit experimental (don't use big numbers, and bit accurate signed arithmetic is not finished yet... we're working on it)

scott_wilson464• 12 years ago

If you are interested in using python for unit testing there is also Cocotb which is a python based library for running verilog and vhdl simulations. It interfaces to the simulator and allows you to stimulate your design directly from python:

https://github.com/potentialventures/cocotb

davidb_• 12 years ago

Bluespec is a language that's getting attention from academia and industry: http://www.bluespec.com/

txomon2• 12 years ago

I would love to use this instead of VHDL, I have been searching for an alternative to those such verbose languages for a long time, but wasn't able to find any.

Where can I download a compiler? How may I start using it? I haven't found any reference of low level that could help me to understand what is the output of the compilers.

txomon2• 12 years ago

I have found everything but the last part, which the output format is... I suppose I will have to download and test it.

MootWoop13• 12 years ago

Good point, we need to make this clearer I think. We (Synflow) have a compiler and IDE that you can download from https://www.synflow.com The compiler and IDE are open source, and the compiler generates VHDL code. We also have additional (proprietary) features that include a Verilog code generator, a C-based simulator, and exporters to third-party tools.

nsiret5• 12 years ago

You can download the tool on www.synflow.com, start using it with our online course on https://eliademy.com/catalog/basic-of-the-cx-language.html and the output of the compilers are VHDL and Verilog.

gothenburg3• 12 years ago

I fail to understand what kind of advantage this language brings to the table compared to the existing solutions.

You touched the subject of the awkward syntax of VHDL. But what about the syntax of Verilog? The syntax seems to be very similar to Verilog.

And besides of the syntax, what are the other features that this language brings that we can't find anywhere else?

And why do you claim that this is oriented "for developers"? Who are these "developers"? Software guys?

MootWoop13• 12 years ago

Don't worry, you're not the first to find that this looks similar to Verilog. I have commented about the syntax aspect on EETimes: see http://www.eetimes.com/author.asp?section_id=36&doc_id=13252...

It's more than the syntax though, it's about having a language for hardware design that most developers (yes software developers) will be able to read, understand, and write. For all sorts of purposes, from playing with FPGAs to designing devices for the IoT. And I think this is something pretty unique :-)

gothenburg3• 12 years ago

What I really wanted was a better explanation of Cx's advantages other than "The syntax is similar to C".

And I'm not sure if you fully understand the difference between a programming language and a hardware description language. Yes, HDL's syntax might be awkward sometimes (whether it's Verilog or VHDL) but I think you are tackling the wrong problems with the wrong way.

Taking the example you gave:

always @(negedge reset_n or posedge clock) begin

  if (~reset_n) begin

    count <= 4'b0;

    FSM <= init;

  end else begin

    case (FSM)

      init: begin

        if (count != 4'h8) begin

          count <= count + 1;

          FSM <= init;

        end else

          FSM <= next_state;

     end

   next_state: // blah

  end
  
 end

end

Can you point exactly what do you think it's wrong with this syntax? And don't compare it with a while() cycle in C, because this is a totally different thing. I'm not saying that this is the perfect way of doing things but there are good reasons why Verilog ended up this way.

I'm really scared with this whole "Hardware design for software developers" thing. Hardware design is very complex and if you aren't careful with what you write, you might end with problems like: CDC, synthesis tools mistaking flip-flops with latches, problems with the insertion of scan chain, and so on.

And by the way, where do you define your clocks in Cx?

correnos2• 12 years ago

One difference from Verilog/VHDL is that Cx will handle state machines for procedural code automatically. Bluespec has a similar facility. Also like Bluespec, it makes the clock implicit which makes a lot of code less noisy.

jclis• 12 years ago

I looked at Bluespec before I tried Cx, it has good points and very powerful features (parameterization of modules comes to mind), but overall I find the semantics to be too complicated for my taste. Rules firing in parallel with custom priorities and possibly non-deterministic?

Quanticles• 12 years ago

The VHDL defines a reset and reset conditions, actually uses a clock, and many other things that the Cx code is leaving out.

MootWoop13• 12 years ago

Exactly! Isn't that a breeze? Reset and clock are implicit by default, but you can always override them (change name, set reset synchronous, etc.)

kw712• 12 years ago

Very cool, I was wondering where the clock was.

chillingeffect• 12 years ago

This is interesting, but if you really want to get user traction, look deeper into how the industry uses HDLs.

For example, one of the most common use cases is scaling code from year-to-year, e.g. the video card market. This means that in 2012, your code works with 16 bits, then 2013, 32, then 2014, 64-bit etc. And you need to keep updating your code to do this, having not touched it for just about six months - perfect time to be kind of familiar but not enough. This is currently handled by integrating perl-like syntax into the HDL. Then it gets "pre-processed" into the proper values in place. It sounds clumsy , but it may be how the machine you're using to read this was made.

A second important use case is integrating writing test code with the source code. As the register, path widths, number of cycles, etc., change, the verification cases have to track. If you could find a way to simplify that, companies would pay a LOT for it.

Another major problem becomes "ifdef-hell" in which sometimes dozens of hierarchical #ifdefs are used to compile and configure HDL code. it's maddening, hence the pre-processor approach.

So, in summary, it's not the clumsy syntax of HDLs that slows progress, it's the ecosystem in which the HDLs are used.

MootWoop13• 12 years ago

Really? Aren't they using VHDL generics/Verilog parameters?

Cx supports specialization of entities with this kind of semantics, so you give an instance parameters and the compiler generates specialized code (so there's no more need for Perl scripts thankfully ^^). Right now you can't enable or disable things, but this is something that would be excellent: modify the hierarchy, add or remove ports, all depending on which flags the entity was instantiated with.

As I explained in another comment a few minutes ago, we're not so much about syntax as we're about better semantics and higher level description (I agree this isn't very clear on the website). Your remark about the ecosystem is perfectly right, and this is what makes EDA a tough market.

I don't know enough about verification to comment. I know SystemVerilog is very powerful but very complex, I've read about UVM and stuff, some people use SystemC. I wonder how they even manage to get hardware validated!

scott_s2• 12 years ago

Advice to the authors: don't stress syntax, but semantics. People here are getting caught up on the notion that "this syntax is not too different from Verilog/VHDL". But that's not the point; it's not what you say, but what that means. You have created a programming model that software people can understand intuitively, but also easily maps to hardware.

People may get hung up on this because the example on your page is so simple. The equivalent VHDL and Verilog is also relatively simple. A simple example is good, and a comparison is good, but just presenting the differences is not enough. Stress what someone coding in Cx does not have to think about. In other words, what are the abstractions in Cx?

Consider what the equivalent page for C versus assembly would look like for a function that computes some simple arithmetic. Some people may say, "Oh, sure, the assembly has a few more lines because you need to push and pop parameters from the stack, but that's no big deal." And it's not - for one function. What's the big deal is that there are entire concepts - saving existing registers, pushing parameters onto the stack, register management - that C programmers don't need to think about. (Most of the time.)

The code you link to elsewhere in this thread hints to me that there are indeed significant abstractions behind Cx, that make it more than just an alternative syntax to Verilog and VHDL. See: https://github.com/synflow/sha-256/blob/master/SHA256/src/co...

MootWoop13• 12 years ago

That's a very good point. In fact the main difference in semantics is that Cx code is structured. Sure in VHDL/Verilog you have functions and if statements and loops. But they can only be used to describe combinational logic. There is a chasm between synchronous logic (everything in a big switch/case) and combinational statements.

Cx supports functions, if and loops for both combinational and synchronous logic. You can have a function that spans over two cycles. You can give parameters to this kind of function just like in software, except that in the end this is all inlined and the state machine is flattened.

The language encourages a higher level of abstraction where you think in terms of blocking reads and data availability rather than "is my signal true". The best is that this can be extended just by changing the port signature, for example to provide rendez-vous style communications (we call it "sync ack" but they're not implemented yet), whereas in HDL you'd have to write a lot of boilerplate code.

Another property is that there is no synthesizable subset in Cx. As far as I know, this is very rare in languages for hardware design, but the language is entirely synthesizable. You never have to think about synthesis versus simulation. Exactly like in software, nobody ever wonders if they can write code that won't run on the processor :-)

And for the example you mention, this is another interesting feature of the language. Because we support sequential loop constructs etc. you can actually write code that works and synthesizes pretty easily, albeit it is slow. And then you can produce a derived version that is optimized :-)

gothenburg3• 12 years ago

"Another property is that there is no synthesizable subset in Cx. As far as I know, this is very rare in languages for hardware design, but the language is entirely synthesizable. You never have to think about synthesis versus simulation. Exactly like in software, nobody ever wonders if they can write code that won't run on the processor :-)"

This is scary. I want the tool to tell me "I can't synthesize this" because when it does, it might infer characteristics of the design that I might not want.

Do you have some kind of paper or detailed explanation about this part?

Sometimes a bad design is not bad because it's badly written, it's bad because it's not complying with some timing constraints or because the synthesis tool decided to infer some crazy system from the code the designer wrote.

The Cx programming language

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