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Viva Vivado!

Xilinx Tunes-Up Tools

As we enter what will perhaps become the “long tail” of Moore’s Law, the traditional battlefield for FPGA companies is shifting dramatically. For most of the history of FPGAs, the main strategic goal was to be “first” on each new process node. If you had FPGAs ready to go on the newest, fastest, densest semiconductor process, you had a significant advantage over your competitor. With each new node, the cost dropped, the power efficiency improved, performance took a leap ahead, and functional density doubled. The combination of those advantages was so substantial that almost nothing your competitor could do would offset a one-node advantage.

Today, however, those new nodes are much harder fought, and the rewards are much more modest. No longer are PPC (performance, power, and cost) automatic “wins” just from moving to the new technology. Leakage current, skyrocketing NRE and mask costs, complex design constraints, and other challenges have forced FPGA companies to make hard compromises among these critical components of semiconductor goodness. Both Xilinx and Altera now have split lines – where “current” devices are not all made on the same process node, and differentiating FPGA product offerings based on process alone has become a losing proposition.

In this new era, other factors are differentiating FPGA companies. Design teams are choosing devices based on available IP, reference designs, specific configurations of hard IP blocks, development boards, packages, and – perhaps most important of all – TOOLS. Design tools are at the heart of every FPGA-based project, and the quality, reliability, ease-of-use, and performance of design tools can literally make or break a project.

Xilinx and Altera, the two big FPGA competitors, have dueled with their tool offerings for years, with some high-stakes, big-drama history to show for it. Altera nearly sank the company just over a decade ago with a disastrous first release of their Quartus tools. The company retrenched and came roaring back, however, and Quartus II – the successor to the ill-fated Quartus – has been giving Xilinx’s aging “ISE” tool suite trouble for years.

Now, however, Xilinx is working to turn the tables with their Vivado tool suite – a ground-up rewrite that took advantage of ASIC-strength technology and modern software development methodologies. Vivado has proven itself quite nicely during its first couple of years, and it’s now beginning to hit its stride as a mature, highly capable design environment.

Now, with the 2014.1 release of Vivado, the company is putting the icing on the cake with a worthwhile bundle of new capabilities. In this latest release, Xilinx has made several “nice to have” improvements – and the first one you’ll notice is an easier, smoother, faster installation flow. Simplified management of installed modules, smaller install images, and an easier installation process are likely to eliminate some of the confusion and frustration up-front.

One of the more interesting things debuting in this version of Vivado is the “Tcl Store.” Tcl (Tool Command Language) is the scripting language on which Vivado itself is based. All of Vivado’s basic underlying functions can be invoked and controlled via Tcl scripts, and Vivado’s user interface is constructed in Tcl. Tcl can therefore be used to easily add to and modify Vivado’s capabilities and features. The Tcl interface opens up a whole world of potentially useful add-ons and plug-ins, and Xilinx has created a “store” – similar to the app stores for smartphones and tablets – that allows the distribution of Tcl modules for Vivado.

The Tcl Store works pretty much like you’d expect, and it is seeded with a small set of useful utilities to help get things started with this first release. The real fun, though, will start if and when the user community begins uploading and sharing helpful Tcl goodies that extend and expand Vivado’s capabilities – and perhaps add some additional domain-specific support for various application areas. So – got a cool Tcl utility for Vivado? Now’s your chance. Get it posted in the store for your big shot at becoming a worldwide Vivado Tcl celebrity – or maybe just to help your fellow designers make a tough job a little bit easier.

One of the lesser-noticed features in Vivado is the tool’s built-in awareness of the configuration of common prototyping and development boards. For many supported boards, Vivado already knows what hardware is on the board and how it’s connected to the FPGA. You don’t have to spend all the effort to describe your board to the tools, and you don’t even have an opportunity to make all the usual mistakes hooking up the correct FPGA pins to the correct peripherals. You can select which of the on-board interfaces you want to use, and Vivado will automatically instantiate the correct blocks in your design – already all wired up to the right pins. While this seems like a simple thing, it is truly a time-saver when you go to populate a dev board with your design.

The biggest challenge in complex FPGA design is clearly meeting all of your design constraints. But perhaps the second-biggest challenge is just getting your constraints specified correctly in the first place – particularly if your design contains large amounts of third-party IP that you didn’t write and perhaps don’t yet understand in detail. Enter Vivado’s new “Timing Constraints Wizard.” The wizard helps you set up your constraints correctly, analyzing your design database and extracting the clocking structure so it can help you identify multi-cycle paths, false paths, paths that cross clock domains, and other typical snags in your constraint setup – perhaps to the chagrin of third-party EDA companies like Blue Pearl, who are working to earn their living by helping you manage some of those same problems.

On the competitive front, Xilinx is offering the first cut at OpenCL synthesis in the HLS portion of this release. OpenCL support is perhaps reactionary on Xilinx’s part, since Altera has been blowing the OpenCL horn for months now. However, starting OpenCL support in HLS signals – even at this early date – that the two companies are taking a fundamentally different approach to OpenCL, and that this difference of approach may even affect the target audience. Altera is clearly going after the software engineer with their OpenCL implementation – targeting applications where OpenCL code might otherwise be used in GPUs for high-performance computing. Xilinx’s decision to put OpenCL into HLS seems to signal that they are going after the hardware designer – offering OpenCL as another option for hardware experts wanting a power tool for building hardware accelerators for performance-critical algorithms. 

It is worth noting that the biggest benefit Vivado brings to Xilinx FPGAs is not in Vivado at all. For the new “Ultrascale” families of devices, Xilinx did exhaustive analysis of the routability of the chip architecture using Vivado. It’s a bit of a dirty little secret in FPGA Land that most FPGAs have historically had insufficient or inefficiently placed routing resources. As a result, we got big cell counts on our FPGAs that we couldn’t really use in real-world designs. As soon as we got to even modest utilizations – sometimes as low as 60-70%, there was a very real chance that our design would not be routable. With Ultrascale, Xilinx ran vast numbers of varying types of designs through the tools and placed-and-routed them on sample chip architectures. They iteratively re-designed the FPGAs themselves until they were consistently getting a very high utilization. This optimization of routing resources leads to FPGAs that we might think of as larger than they appear – because (for a change) we can utilize a very high percentage of the available resources. 

Xilinx says they have improved runtimes, quality-of-results, and ability to use multi-CPU arrays with this release as well. With the size of some of the upcoming Ultrascale devices ranging into the millions of LUT4-equivalent cells, improvements in speed and QoR will be welcome indeed. In fact, when it comes down to the competitive game, it may well be the differences in tools that decide a winner, rather than the differences in chips. If that is the case, Xilinx is staging a strong entry in that tool race with Vivado.

15 thoughts on “Viva Vivado!”

  1. This sounds all nice…

    … and matches the claims of the Xilinx marketing very well.

    My own experience shows that Vivado is not as shiny yet as claimed by the marketing. There are many bugs and issues from tedious (e.g. GUI Crashes) to project critical (e.g. wrong synthesis results).

    Of course developing a new toolsuite is not easy and it is for sure the right step to take but in my eyes there is still a long way to go until Vivado is what is currently claimed by the marketing guys.

  2. @obreund,

    OK, in two consecutive weeks I’ve been said to have sided with first Altera and then Xilinx marketing. I must have the thermostat set about right. (Just kidding – If I’m agreeing with either of them, maybe I should re-calibrate)

    I’ve talked to a number of end-users of Vivado over the past couple of years, and heard a pretty normal gamut of comments for a complex new piece of software. Millions of lines of new code most definitely means customers will find bugs. I’ve heard frustration levels with those bugs ranging from “none at all” to “*&*#*#&@~!” Over the past year, consensus feedback I’ve heard from end-users is that Vivado has gotten consistently more stable and capable, and people are definitely using it productively for real work.

    Marketing probably doesn’t want us to remember or believe that there were bugs in the first place, but that’s not realistic. Bugs have been hit, blood has been spilled, profanities have been uttered. However, based on the cross-section of feedback I’ve heard from actual users, I’d have to give Xilinx good marks on the launch of Vivado – particularly considering the complexity of the undertaking.


  3. Kevin,

    obruend’s description of Vivado is accurate.

    While the Vivado software is improving, it has a very long way to go before being called “mature”, as you have done here.

    I could go on for pages, but a clear illustration of this immaturity is that two years after public launch, the 2014.1 Vivado Synthesis User Guide still lacks[1] any documentation of the supported VHDL and Verilog language constructs.


    [1] http://forums.xilinx.com/t5/Synthesis/CR-Request-Update-UG901-Vivado-Synthesis-User-Guide-to-document/td-p/450122

  4. @Kevin

    It is clear to me that it is not easy to bring-up such a big piece of software. I guess that was also clear to Xilinx when they decided to no longer support ISE/PlanAhead. If ISE/PlanAhead was still supported and could be used as fallback solution, things would not be that bad. But this is not the case today.

    I also don’t expect Vivado to be perfect right now. I understand that it requires time to optimize all the algorithm and find the causes for some occasional crashes. But I am not really willing to work with a tool which does not synthesize my code correctly. I have found two synthesis errors (confirmed by Xilinx) during my current project. If HDL synthesis is not “correct by construction”, the tool is clearly not ready for the market yet.

    There are also conceptual problems. One point is that version control is not really supported. There is no way to use a version control system if you use IP-Integrator in Vivado without hacking TCL scripts by hand. Xilinx nicely calls this “Non-Project based flow” but in reality it means you set up your whole project using scripts, as we did 10 years ago.


  5. Yep sounds like a Xilinx marketing blurb to me.

    Vivado is a very ambitious piece of software.
    Perhaps too ambitious.

    A politician might describe it as a “courageous” .

    It is absolutely riddled with bugs and inconsistencies like a 1 year old corpse in the sun. It’s a shocker. How Xilinx thinks they could charge for such a P.O.S. beats me.

    Do I like it. Yes, it is amazing. It is sensational. Do I hate it. Yes. I might send myself away for 4 weeks on frustration leave.

    Recommended. Yes…. but ensure a good quantity of Scotch near your workstation.

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