Asynchronous Design Tools?

KeggInKenny asks: "I have the opportunity to engage in a research project involving large-scale asynchronous logic circuits. After evaluating possible tools for hardware description, simulation and implementation, I'm finding there's very little targeted toward asynchronous logic. VHDL is little changed from the 1987 standard which is not nearly as suited for large designs as it's name would suggest, and Verilog is too synchronous (or at least it's too easy to fall into the 'synchronous assumption' trap because of Verilog's C-style structure). Specifically: we are designing a low-power microcontroller for portable (read battery-powered) devices, and hoping that through asynchronous logic, we can greatly reduce power consumption. I'd like to see what the hardware gurus from the Slashdot community have to suggest for VLSIC design focusing on asynchronous research. What tools did you use to design the chips, did you run into synthesization problems, and did you find yourselves focusing on many local clocks, as seems to be the current async trend, or true unclocked hardware?"

Comments

From my asynchronous browser

[frenchgates]

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[bsd is dying lololol]

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[awx]

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What the United Nations Must Do

[Anonymous Coward]

Rather than adopting the suggested regime change in Iraq through military force, the United Natioins must instead consider an entirely different course of action. This new course is based upon the facts alone, rather than political pressure. A regime change is indeed necessary, but not in Iraq. The primary regime which needs to be changed, is the one found in Washington DC. The greatest tyrant and true threat to world peace who needs to be ousted, is George W. Bush. The facts which clearly show the need for such a resolution against the U.S. are self evident...they demonstrate a clear and present danger to the world community. America is clearly a nation which aspires to global domination, through the use of the most expensive and high tech military the world has ever known.

In demonstration of the above assertions, let us be very clear about Americas 300+ billion dollar a year expense, for weapons of mass destruction. These include;

1) Atomic and hydrogen bombs.

2) The Star Wars weaponry of space satellites, and laser devices.

3) A host of biological weapons including anthrax, which it has used on its own citizenry and manufactured in its own laboratories.

4) Guided missile cruisers, Stealth bombers and aircraft carriers conveying the most advanced air-based offensives, ever to be used in the history of mankind.

5) Depleted uranium munitions, used repeatedly upon countries such as Yugoslavia, Afghanistan and Iraq, causing birth defects and lingering mutilation of civilian populations.

6) The use of spies, covert CIA operatives and other agents, as well as a barrage of propaganda, which seeks to weaken, overthrow and exploit the sovereign nations of the world, primarily for the sake of installing pro-U.S.-corporate puppets who will do Washington's bidding. [The fact that it has staged countless internal rebellions and coups within dozens of countries in the last five decades, is well documented and known. The U.S. constantly interferes with, and attempts to coerce, the mandates of foreign governments for the sake of its own special interests, and in the name of democracy. The real reason for this behavior is, of course, unfair economic advantage and bottomless greed.]

7) Nerve gas, tear gas, blistering agents, neurotoxins and poisonous compounds of all kinds.

8) Smart bombs, Bunker Buster bombs, Daisy Cutter bombs, mines and laser or satellite guided munitions.

9) Teams of special forces troops, whose m*issions are designed for assassination, covert mass-murder and maximized destruction.

The United States possesses, and has openly discussed using, such weapons of mass destruction upon a great number of other nations. Among these nations are those listed in George Bushs' so-called axis of evil list, as well as many others which it says, harbor terrorists. The so-called War on Terror targets Libya, Yemen, Saudi Arabia, North Korea, Iran, Iraq, Afghanistan, Pakistan, Indonesia, Columbia, Nicaragua and many others. Upon these nations the U.S. has repeatedly issued a series of very aggressive and threatening statements to the effect of; You are either with us or against us, implying dire consequences of economic, diplomatic and military measures in the case of non-compliance. It has openly discussed the possibility of a first strike use of conventional nuclear warheads, and tactical nukes on the battlefield. Its' military policy of, win no matter what the cost of truth or human lives, as a surrogate for sane foreign relations, has earned the wrath of the world. U.S. belligerency has been a major contributor to international hostilities, instability, war and the creation of reactionary terrorist groups, as well as the oppression of peoples worldwide. Its irrational posture threatens to catapult the world into another, and probably final, world war.

The United States has repeatedly shown its willingness to target civilian populations with weapons of mass destruction, especially via the carpet-bombing of cities and infrastructures. It is the only nation to have ever used nuclear devices in war, and upon civilian targets. Among the structures bombed have been desalinization plants, water treatment facilities, police stations, electrical substations and generators, radar and communications stations, hospitals, highway, railway and other transportation facilities, factories for the manufacture of metal, plastic and wood products, and numerous other civilian centers. Countless examples of this behavior have been witnessed in both Iraq and Afghanistan. The result has been millions of Iraqi and Afghan children dying of unnecessary diseases and malnutrition, due to a severe lack of food and safe drinking water. U.S. allies such as Israel, (whose military it literally makes possible) have also exhibited such behavior, as has Great Britain, through constant urging toward mindless, mutually accomplished war frenzies.

A primary export of the United States is weaponry of mass destruction, including so-called conventional weapons such as guided missile cruisers, bombers, small arms, mortars, rockets, tactical advisors, self guided missiles, attack helicopters, high tech surveilance and imaging systems, tanks, explosives and various other tools desigen primarily for the sake of destroying human life. Added to this list of exports are multi-lingual propaganda, biological agents, tear and nerve gas, atomic weapons and their constituents, as well as technical advice regarding their construction, maintenance and use. The U.S. has frequently urged countries to use these weapons against each other so long as it benefitted its political interests, while simultaneously criticizing those who use them without American sanction.

Permanent State of War

The U.S. has repeatedly told its own citizenry to expect involvement in what amounts to a Permanent State of War, due to the War on Terror. A large and increasing number of foreign nationals are being held in American prisons unlawfully, often without charges, legal due process or access to legal counsel. These persons are often subjected to psychological and physical torture due to their nationality or religious beliefs. Its' Afghan prisoners of war in Cuba are treated without dignity, in violation of the Geneva Convention. At the same time, the U.S. has insisted that its military personnel must be held exempt from war crimes charges by the international community, regardless of their actions.

The United States repeatedly defies the resolutions and authority of the United Nations, making is clear that it views this body as merely a tool which can be occasionally used to achieve its special interests, rather than those of humanity in general. America has also made it quite clear that if its desires are not met by the international community/United Nations, that it will act on its own regardless of their wishes, and in whatever manner it sees fit. This includes pre-emptive military invasion of any country which dares to oppose its policies, and for whatever flimsy, baseless justification it gives to the world as an excuse for such actions.

The international community must seriously ask itself, Who's next? in this series of American invasions of sovereign lands. Who will die next...by the thousands, tens of thousands or millions... at the bloody hands of American imperialism?

For these reasons and others, it is hereby proposed that:

A United Nations resolution be created for the purpose of dis-arming and otherwise rendering harmless, the major threat to world peace which the United States has become. Toward this end the necessity of ousting its current dictator, George W. Bush, and the legislative bodies of that government which currently parrot him without serious debate, is self evident.

The functional means necessary to achieve this goal are hereby suggested. They include;

1) Economic sanctions and trade tarriffs, aimed at undermining the U.S. economy, thereby depriving its monstrous military apparatus of the necessary life blood to function.

2) The insistence of a complete withdrawal of all U.S. military forces from wherever they may be stationed around the world. This includes U.S. occupation forces already in conquered countries, (such as Afghanistan).

3) The elimination of world petroleum exports to the United States, as well as the necessary raw materials which make it's industrial-military apparatus possible.

4) The withdrawal of foreign investment in U.S. companies, and their various enterprises. This includes the canceling of existing contracts with U.S. companies, especially those involved with the extraction of petroleum, the mining of precious metals, deforestation, sweat shop industries of clothing, plastics, electronics and other manufacture, as well as other vital resources from lands not within their territorial domain.

5) That U.S. military and civil leaders, especially George W. Bush and his entire cabinet, be brought to justice for their heinous participations in war crimes and crimes against humanity the world over, by the international courts. World leaders must understand that no one country can both make the rules and break them, when it comes to international justice.

6) The use of joint military force if necessary, to curb, restrict and otherwise prevent the American advance toward world domination. America must be deprived of what it most desires, which are the resources of others to fuel an extravagant lifestyle, and the support of bribed or bullied foreign leaders to accomplish a singularly selfish, unilateral agenda.

In effect, the United States must feel the full pressure of international sovereignty, as it expresses its supreme dissatisfaction with the US imperialism around the globe.

The United States must also understand that its anti-humanitarian, corporate-minded, industrial-military schemes for global dominance are nothing short of those employed by Hitler, and other fascist dictators and governments, throughout the course of history. [Constantly declaring war and occupying one country after the next demonstrates this.] The international community, and indeed the peoples of the entire world, find this American attitude and behavior unacceptable. They will no longer be coerced or made to feel insecure in their own places of residence and worship, at the behest of American whims.

Asynchronous logic and Verilog

[eXtro]

Verilog isn't particularily synchronous, in fact, without going to special measures its combinational. You introduce the synchronous behaviour by making conditions happen based on global clocks:

always @ (posedge clock) begin
// do useful stuff
end

I don't know how your particular asynchronous scheme works, but if you were using handshaking (i.e. request/acknowledge) then you would update values and toggle your acknowledge signal based on the completion of your logic operation. These request and ackowledge signals would only propogate between elements.

I don't have a verilog book handy, and I usually design in spice, but something along the lines of
this, at least at the 30000 foot level:

always @ (posedge req0 && req1 && req2) begin
val0 = ip0 | ip1 & ip2;
val1 = ip0 & ip1 | ip2;
ack = 1'b1;
end

Again, I don't know exactly what you're doing, but I'm sure that you can model it with Verilog with increasing levels of detail.

Re:Asynchronous logic and Verilog

[addaon]

"This signature is a secret message encrypted with a one-time-pad"

And they say those things are unbreakable? Got it! Standard xor, byte at a time... you thought we wouldn't catch you?

1d48 081e 0012 4913 0b13 061a 000c 531d 5357 0e52 180c 0d15 4503 4919 0d53 320d 4a34 4100 0a02 520d 1f54 060b 4c1b 0804 1b45 4154 7b45 785a 3a43 454a 1f17 1000

Well...

[Hard_Code]

...from my limited knowledge, "asynchronous" is really just "synchronous" on a much smaller scale. You just have smaller synchronous components that don't have to coordinate synchronously on the global scale. I mean, your adders and stuff are still going to be the same, they will just have their own clock (or no clock I suppose). So my naive assumption is that you have lots of little synchronous components glued logically together with a synchronous coordination bus/fabric. At *some* point it is always synchronous.

Re:Well...

[Omegalomaniac]

...from my limited knowledge, "asynchronous" is really just "synchronous" on a much smaller scale. You just have smaller synchronous components that don't have to coordinate synchronously on the global scale. I mean, your adders and stuff are still going to be the same, they will just have their own clock (or no clock I suppose). So my naive assumption is that you have lots of little synchronous components glued logically together with a synchronous coordination bus/fabric. At *some* point it is always synchronous.

Adders don't have clocks, as I've had to point out to a few students. The inputs to the adders change with the clock, so it is easy to get confused. Asynchronous design is not multi-level synchronous design. It usually involves handshaking, that is one module asks "Are you done yet?" and the other module replies "yep" or "hold on". The purpose of a clock in a synchronous design is to be a taskmaster. The clock says to each module "You will be done at this time!" where "this time" is some integer multiple of the clock.
Contrary to what you said, I would say that at some point all synchronous design is asynchronous. Gates don't have clocks.

Re:Well...

[AlecC]

I don't think this is necessarily true, but it is the way a lot of asynch designs are going. GALS - Globally Asynchronous, Locally Synchronous. Several reasons for this that I can think of. Firstly, asynch is much less well understood, so that by having a design that is 90% synchronous you can limit the unknown risk to the last 10%. Secondly, I think the technology of asynch interconnect is better understood that the sort of deep computation which in a syncronous design would be pipelined. Thirdly, some of the synchronous sub-units are probably availabl off the shelf (even if only from the designers memory). Fourthly, GALS diliver well on some of the advantages of full asynch e.g. spreading the clock noise, allowing different parts to run on clocks of their own speed, avoiding global clock distribution.

However, it is possible to have truly globally asynchronous designs. I could imagin that simulating and testing such a thing could be difficult.

..and that's the point

[kcm]

There are (at least) two ways to utilize asynchronous design architecturally:

The first being a large-scale asynchronous design that allows for high-speed disconnected operations to complete with lots of communication between them, and the second being a design which eliminates the extra latching required in a largely-synchronous design.

The first eats up power, and the second conserves it (theoretically). In the first case, you have tons of little "units" eating up as much power as they can because they're all operating independently as quickly as possible, and in the second case, you have a lot of little units which only "operate" when needed.

Think of it as polling vs. interrupts. One design, the faster one, says "are you done yet? are you done yet? are you done yet? are you done yet? here's your data..", and the other slower and power-conserving design says "hey, I have your data, let me know when you want it and I'll give it to you"..

VHDL'93

[e8johan]

There is a VHDL version from 1993 supported by most major tools and VHDL supports asyncronous designs. I think that you may run into a number of synthetisations issues though as most of todays tools are intended for syncronous designs.

Async tools

[brejc8]

The Async tools page has the list of most tools we use.
Ones we use most often are:

Balsa: make just about anything with it. Its personally quite VHDL like and very well mentained. Recently used to make a whole synthesized ARM compatable asynchronous chip. Comes with many flavours of back end (dual rail, single rail, safe and more).

Petrify: Make small components by describing each part transition by transition. (VSTGL) makes the process a little more graphical.

MINIMALIST: Simmilar to petrify but a little simpler to specify things.

The best way to learn these tools is to go to async 2003 where they have a tutorial of some of them.

There is also the book. It goes through a balsa tutorial.

The most important part of designing async stuff is to learn the different methods. Read the intoductions to some of these theses. They explain the basics. Before you start designing know what makes the system good or not.

Re:Async tools

[awx]

argh! it's you! *grins*

Wondered if you'd pop up here.

Is it semi-finals already?

[Anonymous Coward]

Or are you working on a thesis of some kind? These things already exist, why waste your time?

VHDL is the tool of choice

[Anonymous Coward]

VHDL is event-driven, which is the same as asynchronous in a combinational logic sense, but I don't think a processor can be done in that way. You're going to have to use signal lines to specify when computations are done, and when a register needs to be latched.

Actually, you'd probably want to move the registers into the various computational units (read: alu), and have them signal when the data on them is valid. Signal passing, signal passing, signal passing! :)

Async means a lot of things...

[BDW]

What does it mean to you?

First off, I highly recommend you read some of the ASYNC proceedings. (ASYNC = Nth International Symposium on Asynchronous Circuits and Systems, for N=[1,8]) The best stuff in async tends to get published there. I think they've always published through IEEE, so you can go there, or just do some google searching.

There are no async design flows which you can just drop in to replace Cadence or whatever your current synchronous flow is. There is also a lot of literature (see ASYNC proceedings) on what async people have to do to get commercial synthesis tools to play nice at all. Cadence-style synthesis just isn't there. (Which could be seen as a good thing, depending on your view of the current ack-bassward synchronous flows...)

Your goal sounds close enough to the Manchester ARM work that their tools might work for you. First, read their papers on their ARM work; the devil is always in the details. (Publishing is like sales, you bury the ugly details in the fine print. :) If the experts at Manchester ran into a problem somewhere, odds are good you will too. Second, make sure you completely buy into their sect's interpretation of async before you jump in. They aren't the only sect in town.

I'm academically descended from the QDI culture in SoCal (Caltech, USC, whatever their startup is called these days, ...), so personallly I would go a different route. You should read up on what the QDI folks are doing. They've built their own (in many areas proprietary) flow, but the tools they use are readily available so depending on the complexity of your project you might be able to cook up your own, similar flow with the same tools.

My last point is a word of warning. As much as I like async and would like to see it more widely adopted, you are taking a big plunge, and if this is anything more than a course project, a big risk. Paraphrasing what a man who is much smarter than I said at the last ASYNC: If you read between the lines in the ASYNC proceedings you will see that the async community is basically a small (order hundreds) group of generally very smart people who are highly motivated. As often as not, they get things done by being highly motivated smart people. As a community, we haven't really demonstrated that our techniques to date will work for anyone but highly motivated smart people in the async community.

Look before you leap.

Brian

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[Anonymous Coward]

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