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Messages from 1175

Article: 1175
Subject: Re: VITAL Support Survey
From: Melissa Abato <mla@melissa.topdown>
Date: Thu, 11 May 1995 15:11:47 GMT
Links: << >>  << T >>  << A >>

In article <1995May10.095300.20456@def.bae.co.uk>, <bdickins@def.bae.co.uk> 
writes:

>   VITAL-complient versions of Xilinx's 2000, 3000 and 4000
>   libraries are available from VEDA.
>  
> Does anyone know of any more?

VITAL-compliant version's of Xilinx's 2000, 3000, 4000 and 5000 series
parts will be available next week compiled for MTI V-System on PC and
workstation (and Mentors QuickVHDL).....

Contact:  sales@topdown.com
          Topdown Design Solutions, Inc.
          71 Spit Brook Road, Suite 301
          Nashua, NH   03060





Article: 1176
Subject: Re: Overheating (was Re: Compression algo's for FPGA's)
From: chuckc@sr.hp.com (Chuck Corley)
Date: 11 May 1995 16:55:41 GMT
Links: << >>  << T >>  << A >>
>>Q: Why are FPGA programmers good at typing with either hand?
>>
>>A: Because they need to keep one finger on the FPGA (to see if it
>>is getting hot).

> A better example of good engineering would be to remove the threat.
> *Most* of my digital parts don't flame-out, why should we tolerate it
> of FPGAs?

        I seem to remember that most or all of the 'newer' Xilinx chips
have error-checking done on the configuration bitstream (I don't
remember if have to explicitly enable this feature, check the data
book).

	Hope this helps.

					Chuck Corley
					HP Santa Rosa
					chuckc@sr.hp.com


Article: 1177
Subject: Re: Lattice EPLDs
From: tlue@teleport.com (Todd Lue)
Date: Thu, 11 May 1995 10:30:08
Links: << >>  << T >>  << A >>
In article <3o8ket$1cd@spock.asic.sc.ti.com> clyvb@asic.sc.ti.com (Clive Bittlestone) writes:
>From: clyvb@asic.sc.ti.com (Clive Bittlestone)
>Subject: Re: Lattice EPLDs
>Date: 3 May 1995 19:10:21 GMT

>Anyone got a number for lattice in the US.
>At 16 pounds, I can afford this for my hobby.

Lattice can be reached at 503-681-0118 or in the UK you can call one of their 
reps: Micro Call 44-84-426-1939, Silicon Concepts 44-428-751617







Article: 1178
Subject: Re: Overheating (was Re: Compression algo's for FPGA's)
From: hutch@timp.byu.edu (Brad Hutchings)
Date: 11 May 95 11:25:39
Links: << >>  << T >>  << A >>
>>>>> On 11 May 1995 15:23:57 GMT, billms@corp.mot.com (Bill Mangione-Smith) said:
BS> Nntp-Posting-Host: 129.188.128.4

BS>    hutch@timp.byu.edu (Brad Hutchings) writes:

   >Q: Why are FPGA programmers good at typing with either hand?

   >A: Because they need to keep one finger on the FPGA (to see if it
   >is getting hot).

   >This sounds funny but it turns out to be true for my lab.

BS>    Brad Taylor of GigaOps showed me a very neat feature of their
BS>    XMOD boards at FCCM.  They have a cheap little temperature
BS>    sensor, an op-amp to amplify it, and a cheap little $5
BS>    microcontroller (PIC, I believe) that will shut it all
BS>    down if things get too toasty.  Good engineering.

BS> Doesn't that do nasty things to the end user's cost and board design?

BS> A better example of good engineering would be to remove the threat.
BS> *Most* of my digital parts don't flame-out, why should we tolerate it
BS> of FPGAs?

It is extremely difficult to remove the threat when you are using the
FPGAs in a reconfigurable system. In a static system where all of the
bitstreams are fixed, there isn't much of a problem. However, when you
build a system where it is the intent to allow the user to reconfigure
the resources, I see no way to completely remove the threat. Even if
you check to make sure the bitstream is legal, you cannot guarantee
that the user won't download the wrong bitfile and cause contention
between connected components. The Wildfire people (the people who have
developed Splash-II as a commercial product) have placed resistors
between all of the neighboring FPGAs.  This moves the source of heat
outside of the FPGA but I don't know how practical this will be for
general systems, though.  GigaOp's approach does not add that much in
the way of cost, given the cost of everything else. Remember this is
only an issue for reusable systems. If the silicon is not going to be
reused by the customer or the application developer, this is not a big
deal.

--
            Brad L. Hutchings - (801) 378-2667 - hutch@ee.byu.edu 
Brigham Young University - Electrical Eng. Dept. - 459 CB - Provo, UT 84602
                       Reconfigurable Logic Laboratory



Article: 1179
Subject: Simulation of Xilinc components on VSS..
From: jshah@cs.iastate.edu (Jatan Shah)
Date: 11 May 95 19:41:21 GMT
Links: << >>  << T >>  << A >>

Hi,

	Has anyone performed a gate level simulation of designs
synthesized in synopsys and targetted for the xilinx xc4000 devices.
If so, please  do help me slove my problem.

	I have been trying to simulate the designs meant to be routed
in a xilinx xc4000 device (specifically xc4005).  The XSI interface
provides a set of encrypted VHDL files which contain the entities and
the architectures for the xilinx primitives.  

	I used the xnf2vss utility to generate the vhdl netlist from
the xnf file generated.  Then I used this to simulate the design.  No
errors are flagged, however, apparently the models are not behaving
the way I expect them to.  Every time there is a transition the
simulator flags a 'glitch hazard' , even if there was absolutely no
possibility of a glitch.  So if anybody has experienced the same
problem or is experienced enough to recognize this problem please do
write to me.

Thanx.

I am including a gate level netlist of a single IBUF (a xilinx input
buffer primitive) which did not work.  


Library IEEE,XC4000;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;
use XC4000.components.all;

entity testibuf  is
	port(outpt : out std_logic ; inpt : in std_logic);
end testibuf;

architecture TIMING of testibuf is

begin

   U30 : IBUF Port Map(O => outpt, I => inpt);

end TIMING;

configuration CFG_TESTIBUF_TIMING of TESTIBUF is

    for TIMING
	for 	U30 : IBUF
	    use entity XC4000.IBUF(FTGS);
	end for;
    end for;
end CFG_TESTIBUF_TIMING;


Help will be much appreciated.

Jatan C Shah

Graduate Student
Department of Computer and Electrical Engineering
Iowa State University




Article: 1180
Subject: Re: How to choose an FPGA vendor
From: phillipj@sunny.dab.ge.com (John Phillips)
Date: 11 May 1995 22:33:41 GMT
Links: << >>  << T >>  << A >>
>> >	3. State machine of 20 states running at 60MHz; 1k x 10 bit
>> >	   FIFO at 20MHz; 8 bit counter at 20MHz; several asynchronous
>> >	   latches.

>> Well, no FPGA that I know of has that much INTERNAL ram.  You may be able to pipeline the data 
>> flow to external ram to design this.  However, again 60Mhz is a bit high.

It was anounced, in a recent EE times article, that Altera is coming out with a Flex 8000 family
part with a large on-board RAM.

Do'nt know when it will be available, but such a part should work with this 1 Mhz design.

J.P.




Article: 1181
Subject: Re: Overheating (was Re: Compression algo's for FPGA's)
From: lharold@mrc.uidaho.edu (Len Harold)
Date: 11 May 1995 23:42:06 GMT
Links: << >>  << T >>  << A >>
Chuck Corley (chuckc@sr.hp.com) inspired us with the words:
> >>Q: Why are FPGA programmers good at typing with either hand?
> >>
> >>A: Because they need to keep one finger on the FPGA (to see if it
> >>is getting hot).
> >
> > A better example of good engineering would be to remove the threat.
> > *Most* of my digital parts don't flame-out, why should we tolerate it
> > of FPGAs?
> >
>         I seem to remember that most or all of the 'newer' Xilinx chips
> have error-checking done on the configuration bit-stream (I don't
> remember if have to explicitly enable this feature, check the data
> book).

The CRC error checking is automatic, however this doesn't mean that there
isn't design flaws that will cause latch ups or asynchronous loops.  If your
design switches polarity on all the CLB outputs on all clock cycles then
the FPGA will most definitely burn up.  Last semester a senior design team
cracked the package of FPGA with some sort of a nasty asynchronous loop.

Len
--
 _______________________________________________________________________ 
|      __    ___    ___  _______    _____                               | 
|    /|  |  /\  \  /|  \|\   _   \/\   __\       Len Harold             | 
|   | |  |  \ \   - |   \ \  \_\ /_ \  \_/                              | 
|   | |   \  \ \  \ _|\  \ \   _   \ \  \___     Phone: 208-885-7034    |
|   | |    \  \ \__\/\ \__\ \__\ \__\ \_____\    Fax:   208-885-6840    | 
|   | |*    |  \/__/  \/__/\/__/\/__/\/_____/    Internet: 	        | 
|   |/\     |/\                                    lharold@uidaho.edu   | 
|    \/        \_/\     University of Idaho                             |
|    /|            |    Microelectronics Research Center                |
|   | |            |    NASA Space Engineering Research                 |
|   | |____________|    Center for VLSI System Design                   |
|   |/____________/     WWW[URL]: http://www.mrc.uidaho.edu/            |
|_______________________________________________________________________| 


Article: 1182
Subject: Power consumption of Xilinx FPGAs
From: rr_gregg@tasman.cc.utas.edu.au (Richard Gregg)
Date: 12 May 1995 01:43:37 GMT
Links: << >>  << T >>  << A >>
Does anyone have figures for the power consumption of Xilinx FPGAs,
specifically XC40xx series, and more specifically XC4010D.

I'm interested in average, maximum, and any other figures that you may
have.

Any help would be greatly appreciated.

Richard Gregg

-------------------------------------------------------------------------------
Richard Gregg 
Postgraduate Computer Science
University of Tasmania
rr_gregg@bruny.cc.utas.edu.au
Ph : (002)296519H (002)202951W
-------------------------------------------------------------------------------


Article: 1183
Subject: Anybody using Synario ?
From: Roland <rsimonis@mcs.com>
Date: 12 May 1995 02:34:25 GMT
Links: << >>  << T >>  << A >>
We are now using Xilinx 4010 $ 4013 but 'd like to be device independent 
at the EDA tool level. since we are using PC, we see X-mplar, Viewlogic 
and Synario as possible candidates. 
Synario's demonstration is the most impressive. Anybody with hands-on 
experience? 
We are also wondering how to tweak things w/ those tools, as we often 
have to play with the routing to get the speed.
Thanx




Article: 1184
Subject: Re: Overheating (was Re: Compression algo's for FPGA's)
From: pchong@calum.csclub.uwaterloo.ca (Phil Chong)
Date: Fri, 12 May 1995 04:30:35 GMT
Links: << >>  << T >>  << A >>
In article <3otfid$jb6@canyon.sr.hp.com>,
Chuck Corley <chuckc@sr.hp.com> wrote:
>>>Q: Why are FPGA programmers good at typing with either hand?
>>>
>>>A: Because they need to keep one finger on the FPGA (to see if it
>>>is getting hot).

Been there.  Done that.  :)

>        I seem to remember that most or all of the 'newer' Xilinx chips
>have error-checking done on the configuration bitstream (I don't
>remember if have to explicitly enable this feature, check the data
>book).

This brings up a concern I have...As I understand it, turning the CRC on
for the Xilinx 4000 series simply sets a few bits in the bitstream, so that
when the 4000 reads it, it says, "Aha!  I have to check the CRC!" and if
the following bitstream fails the CRC check, it resets.  Otherwise,
the default is not to verify the CRC and accept the bitstream completely.

Now, say a corrupted bitstream did *not* have the CRC "check on" bits set;
i.e. the corruption mangled these bits.  The FPGA would then ignore the
CRC and download the bad bitstream.

Is this correct?  Doesn't it seem a bit silly to have a disabled CRC as
a default?  (Or for that matter, any sort of disabled CRC option at all?
I mean, the various framing bits in the bitstream are fairly useless
anyways, why not use them for some sort of CRC/checksum?)


Phil


Article: 1185
Subject: Re: Overheating (was Re: Compression algo's for FPGA's)
From: randraka@ids.net
Date: Fri, 12 May 95 10:13:48 +500
Links: << >>  << T >>  << A >>
In Article <HUTCH.95May11112539@timp.byu.edu>
hutch@timp.byu.edu (Brad Hutchings) writes:
>
>It is extremely difficult to remove the threat when you are using the
>FPGAs in a reconfigurable system. In a static system where all of the
>bitstreams are fixed, there isn't much of a problem. However, when you
>build a system where it is the intent to allow the user to reconfigure
>the resources, I see no way to completely remove the threat. Even if
>you check to make sure the bitstream is legal, you cannot guarantee
>that the user won't download the wrong bitfile and cause contention
>between connected components. The Wildfire people (the people who have
>developed Splash-II as a commercial product) have placed resistors
>between all of the neighboring FPGAs.  This moves the source of heat
>outside of the FPGA but I don't know how practical this will be for
>general systems, though.  GigaOp's approach does not add that much in
>the way of cost, given the cost of everything else. Remember this is
>only an issue for reusable systems. If the silicon is not going to be
>reused by the customer or the application developer, this is not a big
>deal.
>
>--
Many of you responding to this thread have mentioned Xilinx.  In a single
Xilinx, this is normally NOT a problem, even if the part is being reloaded with
new programs during the course of its operation.  The heat problems Brad refers
to are a result of partial reconfiguration where a portion of the device
remains running with its original programming while another portion is
reprogrammed (yes there are devices out there that support this mode).  In that
case, as he mentions, the user must be extremely careful about the output
connections from every cell during the course of partial reconfiguration.  Even
if the circuit is connected properly at the end of the reconfig, you can get
momentary contention during the process depending on the order that the cell
functions are changed.  
 
In the case of xilinx, you don't have to worry about these problems, since
xilinx doesn't support partial reconfiguratiion!  Of course you will also have
considerable challenges in trying to do what Brad is doing without the ability
to partially reconfigure.  The closest you come with Xilinx is to use a tiled
approach where a system consisting of multiple xilinx can be partially
reconfigured by changing the programs in a subset of the xilinx chips.  Here,
you can run into the problem at a higher level (only at the I/O of the Xilinx
chips).  That is what Brad was referring to when he mentioned the resistors
between devices. 
 
Hope this clears some of the apparent confusion.

-Ray Andraka
Chairman, the Andraka Consulting Group
401/884-7930    FAX 401/884-7950
email randraka@ids.net
 
The Andraka Consulting Group is a digital hardware design firm specializing in
obtaining the maximum performance from FPGAs.  Services include complete
design, development, simulation, and integration of these devices and the
surrounding circuits.  We also evaluate, troubleshoot, and improve existing
designs.  Please call or write for a free brochure.



Article: 1186
Subject: Verilog Won & VHDL Lost? -- You Be The Judge!
From: jcooley@world.std.com (John Cooley)
Date: Fri, 12 May 1995 06:20:58 GMT
Links: << >>  << T >>  << A >>

   !!!     "It's not a BUG,                           jcooley@world.std.com
  /o o\  /  it's a FEATURE!"                                 (508) 429-4357
 (  >  )
  \ - /       The Unexpected Results From A Hardware Design Contest:
  _] [_           Verilog Won & VHDL Lost? -- You Be The Judge!

                       by John Cooley, the ESNUG guy

        Holliston Poor Farm, P.O. Box 6222, Holliston, MA  01746-6222


I knew I hit a nerve.  Usually when I publish a candid review of a particular
conference or EDA product I typically see around 85 replies in my e-mail "in"
box.  Buried in my review of the recent Synopsys Users Group meeting, I very
tersely reported that 8 out of the 9 Verilog designers managed to complete
the conference's design contest yet *none* of the 5 VHDL designers could.  I
apologized for the terseness and promised to do a detailed report on the
design contest at a later date.  Since publishing this, my e-mail "in" box
has become a veritable Verilog/VHDL Beirut filling up with 169 replies!  Once
word leaked that the detailed contest write-up was going to be published in
the DAC issue of "Integrated System Design" (formerly "ASIC & EDA" magazine),
I started getting phone calls from the chairman of VHDL International,
Mahendra Jain, and from the president of Open Verilog International, Bill
Fuchs.  A small army of hired gun spin doctors (otherwise know as PR agents)
followed with more phone calls.  I went ballistic when VHDL columnist Larry
Saunders had approached the Editor-in-Chief of ISD for an advanced copy of my
design contest report.  He felt I was "going to do a hatchet job on VHDL" and
wanted to write a rebuttal that would follow my article...  and all this was
happening before I had even written *one* damned word of the article!

Because I'm an independent consultant who makes his living training and
working *both* HDL's, I'd rather not go through a VHDL Salem witch trial
where I'm publically accused of being secretly in league with the Devil to
promote Verilog, thank you.  Instead I'm going present *everything* that
happened at the Design Contest, warts and all, and let *you* judge!  At the
end of court evidence, I'll ask you, the jury, to write an e-mail reply which
I can publish in my column in the follow-up "Integrated System Design".


The Unexpected Results
----------------------

Contestants were given 90 minutes using either Verilog or VHDL to create a
gate netlist for the fastest fully synchronous loadable 9-bit increment-by-3
decrement-by-5 up/down counter that generated even parity, carry and borrow.

Of the 9 Verilog designers in the contest, only 1 didn't get to a final gate
level netlist because he tried to code a look-ahead parity generator.  Of the
8 remaining, 3 had netlists that missed on functional test vectors.  The 5
Verilog designers who got fully functional gate-level designs were:

   Larry Fiedler     NVidea               3.90 nsec     1147 gates
   Steve Golson      Trilobyte Systems    4.30 nsec     1909 gates
   Howard Landman    HaL Computer         5.49 nsec     1495 gates
   Mark Papamarcos   EDA Associates       5.97 nsec     1180 gates
   Ed Paluch         Paluch & Assoc.      7.85 nsec     1514 gates

The surprize was that, during the same time, *none* of 5 VHDL designers in
the contest managed to produce any gate level designs.


Not VHDL Newbies vs. Verilog Pro's
----------------------------------

The first reaction I get from the VHDL bigots (who weren't at the competition)
is: "Well, this is obviously a case where Verilog veterans whipped some VHDL
newbies.  Big deal."  Well, they're partially right.  Many of those Verilog
designers are damned good at what they do -- but so are the VHDL designers!

I've known Prasad Paranjpe of LSI Logic for years.  He has taught and still
teaches VHDL with synthesis classes at U.C. Santa Cruz University Extention
in the heart of Silicon Valley.  He was VP of the Silicon Valley VHDL Local
Users Group.  He's been a full time ASIC designer since 1987 and has designed
*real* ASIC's since 1990 using VHDL & Synopsys since rev 1.3c.  Prasad's home
e-mail address is "vhdl@ix.netcom.com" and his home phone is (XXX) XXX-VHDL.
ASIC designer Jan Decaluwe has a history of contributing insightful VHDL and
synthesis posts to ESNUG while at Alcatel and later as a founder of Easics,
a European ASIC design house.  (Their company motto: "Easics - The VHDL
Design Company".)  Another LSI Logic/VHDL contestant, Vikram Shrivastava, has
used the VHDL/Synopsys design approach since 1992.  These guys aren't newbies!


Creating The Contest
--------------------

I followed a double blind approach to putting together this design contest.
That is, not only did I have Larry Saunders (a well known VHDL columnist)
and Yatin Trivedi (a well known Verilog columnist), both of Seva Technologies
comment on the design contest -- unknown to them I had Ken Nelsen (a VHDL
oriented Methodology Manager from Synopsys) and Jeff Flieder (a Verilog based
designer from Ford Microelectronics) also help check the design contest for
any conceptual or implementation flaws.

My initial concern in creating the contest was to not have a situation where
the Synopsys Design Compiler could quickly complete the design by just
placing down a DesignWare part.  Yet, I didn't want to have contestants
trying (and failing) to design some fruity, off-the-wall thingy that no one
truely understood.  Hence, I was restricted to "standard" designs that all
engineers knew -- but with odd parameters thrown in to keep DesignWare out
of the picture.  Instead of a simple up/down counter, I asked for an up-by-3
and down-by-5 counter.  Instead of 8 bits, everything was 9 bits.

                                  recycled COUNT_OUT [8:0]
                     o---------------<---------------<-------------------o
                     |                                                   |
                     V                                                   |
               -------------                     --------                |
  DATA_IN -->-|   up-by-3   |->-----carry----->-| D    Q |->- CARRY_OUT  |
   [8:0]      |  down-by-5  |->-----borrow---->-| D    Q |->- BORROW_OUT |
              |             |                   |        |               |
       UP -->-|    logic    |                   |        |               |
     DOWN -->-|             |-o------->---------| D[8:0] |               |
               -------------  | new_count [8:0] | Q[8:0] |->-o---->------o
                              |                 |        |   |
                 o------<-----o        CLOCK ---|>       |   o->- COUNT_OUT
                 |                               --------           [8:0]
 new_count [8:0] |     -----------
                 |    |   even    |              --------
                 o-->-|  parity   |->-parity-->-| D    Q |->- PARITY_OUT
                      | generator |   (1 bit)   |        |
                       -----------           o--|>       |
                                             |   --------
                                   CLOCK ----o

   Fig.1) Basic block diagram outlining design's functionality

The even PARITY, CARRY and BORROW requirements were thrown in to give the
contestants some space to make significant architectural trade-offs that
could mean the difference between winning and losing.

The counter loaded when the UP and DOWN were both "low", and held its state
when UP and DOWN were "high" -- exactly opposite to what 99% of the world's
loadable counters traditionally do.

                  UP  DOWN   DATA_IN    |    COUNT_OUT    
                 -----------------------------------------
                   0    0     valid     |   load DATA_IN
                   0    1   don't care  |     (Q - 5)
                   1    0   don't care  |     (Q + 3)
                   1    1   don't care  |   Q unchanged

   Fig. 2) Loading and up/down counting specifications.  All I/O events
           happen on the rising edge of CLOCK.

To spice things up a bit further, I chose to use the LSI Logic 300K ASIC
library because wire loading & wire delay is a significant factor in this
technology.  Having the "home library" advantage, one saavy VHDL designer,
Prasad Paranjpe of LSI Logic, cleverly asked if the default wire loading
model was required (he wanted to use a zero wire load model to save in
timing!)  I replied: "Nice try.  Yes, the default wire model is required."

To let the focus be on design and not verification, contestants were given
equivalent Verilog and VHDL testbenches provided by Yatin Trivedi & Larry
Saunder's Seva Technologies.  These testbenches threw the same 18 vectors at
the Verilog/VHDL source code the contestants were creating and if it passed,
for contest purposes, their design was judged "functionally correct."

For VHDL, contestants had their choice of Synopsys VSS 3.2b and/or Cadence
Leapfrog VHDL 2.1.4; for Verilog, contestants had their choice of Cadence
Verilog-XL 2.1.2 or Chronologic VCS 2.3.2 plus their respective Verilog/VHDL
design environments.  (The CEO of Model Technology Inc., Bob Hunter, was too
paranoid about the possiblity of Synopsys employees seeing his VHDL to allow
it in the contest.)  LCB 300K rev 3.1A.1.1.101 was the LSI Logic library.

I had a concern that some designers might not know that an XOR reduction tree
is how one generates parity -- but Larry, Yatin, Ken & Jeff all agreed that
any engineer not knowing this shouldn't be helped to win a design contest.
As a last minute hint, I put in every contestant's directory an "xor.readme"
file that named the two XOR gates available in LSI 300K library (EO and EO3)
plus their drive strengths and port lists.

To be friendly synthesis-wise, I let the designers keep the unrealistic
Synopsys default setting of all inputs having infinite input drive strength
and all outputs were driving zero loads.

The contest took place in three sessions over the same day.  To keep things
equal, my guiding philosophy throughout these sessions was to conscientiously
*not* fix/improve *anything* between sessions -- no matter how frustrating!

After all that was said & done, Larry & Yatin thought that the design contest
would be too easy while Ken & Jeff thought it would have just about the right
amount of complexity.  I asked all four if they saw any Verilog or VHDL
specific "gotchas" with the contest; all four categorically said "no."


Murphy's Law
------------

Once the contest began, Murphy's Law -- "that which can go wrong, will go
wrong" -- prevailed.  Because we couldn't get the SUN and HP workstations
until a terrifying 3 days before the contest, I lived through a nightmare
domino effect on getting all the Verilog, VHDL, Synopsys and LSI libraries
in and installed.  Nobody could cut keys for the software until the machine
ID's were known -- and this wasn't until 2 days before the contest!  (As it
was, I had to drop the HP machines because most of the EDA vendors couldn't
cut software keys for HP machines as fast as they could for SUN workstations.)

The LSI 300K Libraries didn't arrive until an hour before the contest began.
The Seva guys found and fixed a bug in the Verilog testbench (that didn't
exist in the VHDL testbench) some 15 minutes before the constest began.

Some 50 minutes into the first design session, one engineer's machine
crashed -- which also happened to be the licence server for all the Verilog
simulation software!  (Luckily, by this time all the Verilog designers were
deep into the synthesis stage.)  Unfortunately, the poor designer who had his
machine crash couldn't be allowed to redo the contest in a following session
because of his prior knowlege of the design problem.  This machine was
rebooted and used solely as a licence server for the rest of the contest.

The logistics nightmare once again reared its ugly head when two designers
innocently asked: "John, where are your Synopsys manuals?"  Inside I screamed
to myself: "OhMyGod! OhMyGod! OhMyGod!"; outside I calmly replied: "There are
no manuals for any software here.  You have to use the online docs available."

More little gremlins danced in my head when I realized that six of the eight
data books that the LSI lib person brought weren't for the *exact* LCB 300K
library we were using -- these data books would be critical for anyone trying
to hand build an XOR reduction tree -- and one Verilog contestant had just
spent ten precious minutes reading a misleading data book!  (There were two
LCB 300K, one LCA 300K and five LEA 300K databooks.)  Verilog designer Howard
Landman of HaL Computer noted: "I probably wasted 15 minutes trying to work
through this before giving up and just coding functional parity -- although
I used parentheses in hopes of Synopsys using 3-input XOR gates."

Then, just as things couldn't get worst, everyone got to discover that when
Synopsys's Design Compiler runs for the first time in a new account -- it
takes a good 10 to 15 minutes to build your very own personal DesignWare
cache.  Verilog contestant Ed Paluch, a consultant, noted: "I thought that
first synthesis run building [expletive deleted] DesignWare caches would
*never* end!   It felt like days!"

Although, in my opinion, none of these headaches compromised the integrity of
the contest, at the time I had to continually remind myself: "To keep things
equal, I can *not* fix nor improve *anything* no matter how frustrating."


Judging The Results
-------------------

Because I didn't want to be in the business of judging source code *intent*,
all judging was based solely on whether the gate level passed the previously
described 18 test vectors.  Once done, the design was read into the Synopsys
Design Compiler and all constraints were removed.  Then I applied the command
"clocks_at 0, 6, 12 clock" and then took the longest path as determined by
"report_timing -path full -delay max -max_paths 12" as the final basis for
comparing designs -- determining that Verilog designer Larry Fiedler of
NVidia won with a 1147 gate design timed at 3.90 nsec.

      reg [9:0] cnt_up, cnt_dn;   reg [8:0] count_nxt;

      always @(posedge clock)
      begin
        cnt_dn = count_out - 3'b 101;  // synopsys label add_dn
        cnt_up = count_out + 2'b 11;   // synopsys label add_up

        case ({up,down})
           2'b 00 : count_nxt = data_in;
           2'b 01 : count_nxt = cnt_dn;
           2'b 10 : count_nxt = cnt_up;
           2'b 11 : count_nxt = 9'bX;  // SPEC NOT MET HERE!!!
          default : count_nxt = 9'bX;  // avoiding ambiguity traps
        endcase

        parity_out  <= ^count_nxt;
        carry_out   <= up & cnt_up[9];
        borrow_out  <= down & cnt_dn[9];
        count_out   <= count_nxt;
      end

 Fig. 3) The winning Verilog source code.  (Note that it failed to meet
         the spec of holding its state when UP and DOWN were both high.)

Since judging was open to any and all who wanted to be there, Kurt Baty, a
Verilog contestant and well respected design consultant, registered a vocal
double surprize because he knew his design was of comparable speed but had
failed to pass the 18 test vectors.  (Kurt's a good friend -- I really
enjoyed harassing him over this discovery -- especially since he had bragged
to so many people on how he was going to win this contest!)  An on the spot
investigation yielded that Kurt had accidently saved the wrong design in the
final minute of the contest.  Even further investigation then also yielded
that the 18 test vectors didn't cover exactly all the counter's specified
conditions.  Larry's "winning" gate level Verilog based design had failed to
meet the spec of holding its state when UP and DOWN were high -- even though
his design had successfully passed the 18 test vectors!

If human visual inspection of the Verilog/VHDL source code to subjectively
check for places where the test vectors might have missed was part of the
judging criteria, Verilog designer Steve Golson would have won.  Once again,
I had to reiterate that all designs which passed the testbench vectors were
considered "functionally correct" by definition.


What The Contestants Thought
----------------------------

Despite NASA VHDL designer Jeff Solomon's "I didn't like the idea of taking
the traditional concept of counters and warping it to make a contest design
problem", the remaining twelve contestants really liked the architectural
flexiblity of the up-by-3/down-by-5, 9 bit, loadable, synchronous counter
with even party, carry and borrow.  Verilog designer Mark Papamarcos summed
up the majority opinion with: "I think that the problem was pretty well
devised.  There was a potential resource sharing problem, some opportunities
to schedule some logic to evaluate concurrently with other logic, etc.  When
I first saw it, I thought it would be very easy to implement and I would have
lots of time to tune.  I also noticed the 2 and 3-input XOR's in the top-level
directory, figured that it might be somehow relevant, but quickly dismissed
any clever ideas when I ran into problems getting the vectors to match."

Eleven of contestants were tempted by the apparent correlation between known
parity and the adding/subtracting of odd numbers.  Only one Verilog designer,
Oren Rubinstein of Hewlett-Packard Canada, committed to this strategy but ran
way out of time.  Once home, Kurt Baty helped Oren conceptually finish his
design while Prasad Paranjpe helped with the final synthesis.  It took about
7 hours brain time and 8 hours coding/sim/synth time (15 hours total) to get
a final design of 3.05 nsec & 1988 gates.  Observing it took 10x the original
estimated 1.5 hours to get a 22% improvement in speed, Oren commented: "Like
real life, it's impossible to create accurate engineering design schedules."

Two of the VHDL designers, Prasad Paranjpe of LSI Logic and Jan Decaluwe of
Easics, both complained of having to deal with type conversions in VHDL.
Prasad confessed: "I can't believe I got caught on a simple typing error.
I used IEEE std_logic_arith, which requires use of unsigned & signed subtypes,
instead of std_logic_unsigned."  Jan agreed and added: "I ran into a problem
with VHDL or VSS (I'm still not sure.)  This case statement doesn't analyze:
"subtype two_bits is unsigned(1 downto 0); case two_bits'(up & down)..."  But
what worked was: "case two_bits'(up, down)..."  Finally I solved this problem
by assigning the concatenation first to a auxiliary variable."

Verilog competitor Steve Golson outlined the first-get-a-working-design-and-
then-tweak-it-in-synthesis strategy that most of the Verilog contestants
pursued with: "As I recall I had some stupid typos which held me up; also I
had difficulty with parity and carry/borrow.  Once I had a correctly
functioning baseline design, I began modifying it for optimal synthesis.
My basic idea was to split the design into four separate modules: the adder,
the 4:1 MUXes, the XOR logic (parity and carry/borrow), and the top counter
module which contains only the flops and instances of the other three modules.
My strategy was to first compile the three (purely combinational) submodules
individually.  I used a simple "max_delay 0 all_outputs()" constraint on each
of them. The top-level module got the proper clock constraint.  Then
"dont_touch" these designs, and compile the top counter module (this just
builds the flops).  Then to clean up I did an "ungroup -all" followed by a
"compile -incremental" (which shaved almost 1 nsec off my critical path.)"

Typos and panic hurt the performance of a lot of contestants.  Verilog
designer Daryoosh Khalilollahi of National Semiconductor said: "I thought 
I would not be able to finish it on time, but I just made it.  I lost some
time because I would get a Verilog syntax error that turned up because I had
one extra file in my Verilog "include" file (verilog -f include) which was
not needed."  Also, Verilog designer Howard Landman of Hal Computers never
realized he had put both a complete behavioral *and* a complete hand
instanced parity tree in his source Verilog.  (Synopsys Design Compiler just
optimized one of Howard's dual parity trees away!)

On average, each Verilog designer managed to get two to five synthesis runs
completed before running out of time.  Only two VHDL designers, Jeff Solomon
and Jan Decaluwe, managed to start (but not complete) one synthesis run.  In
both cases I disqualified them from the contest for not making the deadline
but let their synthesis runs attempt to finish.  Jan arrived a little late so
we gave Jan's run some added time before disqualifying him.  His unfinished
run had to be killed after 21 minutes because another group of contestants
were arriving.  (Incidently, I had accidently given the third session an
extra 6 design minutes because of a goof on my part.  No Verilog designers
were in this session but VHDL designers Jeff Solomon, Prasad Paranjpe, Vikram
Shrivastava plus Ravi Srinivasan of Texus Instruments all benefited from this
mistake.)  Since Jeff was in the last session, I gave him all the time needed
for his run to complete.  After an additional 17 minutes (total) he produced
a gate level design that timed out to 15.52 nsec.  After a total of 28 more
minutes he got the timing down to 4.46 nsec but his design didn't pass
functional vectors.  He had an error somewhere in his VHDL source code.

Failed Verilog designer Kurt Baty closed with: "John, I look forward to next
year's design contest in whatever form or flavor it takes, and a chance to
redeem my honor."


Closing Arguments To The Jury
-----------------------------

Closing aurguments the VHDL bigots may make in this trial might be: "What 14
engineers do isn't statistically significant.  Even the guy who ran this
design contest admitted all sorts of last minute goofs with it.   You had a
workstation crash, no manuals & misleading LSI databooks.  The test vectors
were incomplete.  One key VHDL designer ran into a Synopsys VHDL simulator
bug after arriving late to his session.  The Verilog design which won this
contest didn't even meet the spec completely!  In addition, this contest
wasn't put together to be a referendum on whether Verilog or VHDL is the
better language to design in -- hence it may miss some major issues."

The Verilog bigots might close with: "No engineers work under the contrived
conditions one may want for an ideal comparision of Verilog & VHDL. Fourteen
engineers may or may not be statistally significant, but where there's smoke,
there's fire.  I saw all the classical problems engineers encounter in day to
day designing here.  We've all dealt with workstation crashes, bad revision
control, bugs in tools, poor planning and incomplete testing.  It's because
of these realities I think this design contest was *perfect* to determine how
each HDL measures up in real life.  And Verilog won hands down!"

The jury's veridict will be seen in the next "Integrated System Design".


You The Jury...
---------------

You the jury are now asked to please take ten minutes to think about what
you have just read and, in 150 words or less, send your thoughts to me at
"jcooley@world.std.com".  Please don't send me "VHDL sucks." or "Verilog
must die!!!" -- but personal experiences and/or observations that add to
the discussion.  It's OK to have strong/violent opinions, just back them with
something more than hot air.  (Since I don't want to be in the business of
chasing down permissions, my default setting is *whatever* you send me is
completely publishable.  If you wish to send me letters with a mix of
publishable and non-publishable material CLEARLY indicate which is which.)
I will not only be reprinting replied letters, I'll also be publishing stats
on how many people had reported each type of specific opinion/experience.

                           - John Cooley
                             Part Time EDA Consumer Advocate
                             Full Time ASIC, FPGA & EDA Design Consultant

P.S. In replying, please indicate your job, your company, whether you use
     Verilog or VHDL, why, and for how long.  Also, please DO NOT copy
     this article back to me -- I know why you're replying!  :^)

===========================================================================
 Trapped trying to figure out a Synopsys bug?  Want to hear how 3349 other
 users dealt with it ?  Then join the E-Mail Synopsys Users Group (ESNUG)!
 
      !!!     "It's not a BUG,               jcooley@world.std.com
     /o o\  /  it's a FEATURE!"                 (508) 429-4357
    (  >  )
     \ - /     - John Cooley, EDA & ASIC Design Consultant in Synopsys,
     _] [_         Verilog, VHDL and numerous Design Methodologies.

     Holliston Poor Farm, P.O. Box 6222, Holliston, MA  01746-6222
   Legal Disclaimer: "As always, anything said here is only opinion."


Article: 1187
Subject: Re: Power consumption of Xilinx FPGAs
From: Yuce Beser <yuce@sh.bel.alcatel.be>
Date: 12 May 1995 13:03:50 GMT
Links: << >>  << T >>  << A >>
Hi,
Here is some figures from the Xilinx data book,

Dynamic power consumption, XC4010: (Average values)
One CLB driving 3 local interconnects	0.3mW /MHz
One device output with a 50pF load	1.2mW /MHz
One Global clock buffer & line		5.1mW /MHz
One split longline without driver	0.24 mW /MHz

For more info you may also contact hotline@xilinx.com

Yuce Beser



Article: 1188
Subject: Re: Power consumption of Xilinx FPGAs
From: Yuce Beser <yuce@sh.bel.alcatel.be>
Date: 12 May 1995 13:04:11 GMT
Links: << >>  << T >>  << A >>
Hi,
Here is some figures from the Xilinx data book,

Dynamic power consumption, XC4010: (Average values)
One CLB driving 3 local interconnects	0.3mW /MHz
One device output with a 50pF load	1.2mW /MHz
One Global clock buffer & line		5.1mW /MHz
One split longline without driver	0.24 mW /MHz

For more info you may also contact hotline@xilinx.com

Yuce Beser



Article: 1189
Subject: Re: Power consumption of Xilinx FPGAs
From: Yuce Beser <yuce@sh.bel.alcatel.be>
Date: 12 May 1995 13:04:40 GMT
Links: << >>  << T >>  << A >>
Hi,
Here is some figures from the Xilinx data book,

Dynamic power consumption, XC4010: (Average values)
One CLB driving 3 local interconnects	0.3mW /MHz
One device output with a 50pF load	1.2mW /MHz
One Global clock buffer & line		5.1mW /MHz
One split longline without driver	0.24 mW /MHz

For more info you may also contact hotline@xilinx.com

Yuce Beser



Article: 1190
Subject: Re: Power consumption of Xilinx FPGAs
From: Yuce Beser <yuce@sh.bel.alcatel.be>
Date: 12 May 1995 13:11:19 GMT
Links: << >>  << T >>  << A >>
Hi,
Here is some figures from the Xilinx data book,

Dynamic power consumption, XC4010: (Average values)
One CLB driving 3 local interconnects	0.3mW /MHz
One device output with a 50pF load	1.2mW /MHz
One Global clock buffer & line		5.1mW /MHz
One split longline without driver	0.24 mW /MHz

For more info you may also contact hotline@xilinx.com

Yuce Beser



Article: 1191
Subject: Re: Is anybody using FPGA's to do PCI interfaces?
From: rhperez@aol.com (RHPerez)
Date: 12 May 1995 11:13:52 -0400
Links: << >>  << T >>  << A >>
ATT has an app note, including the VHDL code used by
one of their customers to build a PCI-bus interface.
You can use the code to test it, but as I understand
you can't use the code to build a product, without paying
royalties to the company that wrote it.

Xilinx and Altera both say they can do PCI as well.


Article: 1192
Subject: Re: Anybody using Synario ?
From: rhperez@aol.com (RHPerez)
Date: 12 May 1995 11:20:54 -0400
Links: << >>  << T >>  << A >>
I don't know how good Synario's VHDL simulator is,
but we've had excellent results with Modeltech.
We use Exemplar as our synthesizer.  Again,
excellent results.

Both companies have given great customer support
when we've had questions (even on things that weren't
really their problem).

I'd definitely talk to both companies about what you
want to do - Exemplar resells Modeltech now, and
has it incorporated into their Galileo product, which
is Modeltech, the Exemplar synthesizer, and
a static timing analyzer.


Article: 1193
Subject: Re: Verilog Won & VHDL Lost? -- You Be The Judge!
From: rhperez@aol.com (RHPerez)
Date: 12 May 1995 11:26:54 -0400
Links: << >>  << T >>  << A >>
I'd like to make a recommendation in the future:

- have someone implement the design ahead of time.
- run faultsimulation on it, and get to 100% coverage.

That way, you'll know that your stimulus correctly
tests the design.

Also, you might want to see if you can get Sun to
lend a portable Sun ahead of time.  Then, you can set
it up as the license server with floating licenses.

This should save some stress.



Article: 1194
Subject: Re: How to choose an FPGA vendor
From: rhperez@aol.com (RHPerez)
Date: 12 May 1995 11:34:28 -0400
Links: << >>  << T >>  << A >>
On the multipliers: Can you use bit-serial, and use a high-speed clock?

That's the only way I think you can get multipliers into an FPGA, without
using up all your real-estate.


Article: 1195
Subject: VMEbus interface logic in FPGA?
From: grunbem@dps-hobbit.pgh.wec.com (Michael Grunberg)
Date: 12 May 1995 16:07:41 GMT
Links: << >>  << T >>  << A >>
	Anyone knows of a VMEbus foundation logic "macro", that could be imported in a FPGA design? (It should be preferrably in a schematic form, but HDL is okay too.)

	Thank you in advance!

Mike

P.S. Please e-mail directly to me, also.



Article: 1196
Subject: Re: How to choose an FPGA vendor
From: husby@fnal.gov (Don Husby)
Date: 12 May 1995 16:08:02 GMT
Links: << >>  << T >>  << A >>
In article <3ovv64$1f3@newsbf02.news.aol.com>, rhperez@aol.com (RHPerez) says:
>
> On the multipliers: Can you use bit-serial, and use a high-speed clock?
>
> That's the only way I think you can get multipliers into an FPGA, without
> using up all your real-estate.

Yes.  It's a trade off between speed and resource use.
You can use bit-serial, nibble serial, etc.
Your clock speed is still limited by the toggle speed of the
logic blocks, but can approach 10ns for a well pipelined "inner loop".

There have been several articles and app notes written on
the topic of FPGA multipliers.  Some work especially well if
you are multiplying a stream of numbers by a slowly-changing
constant.


Article: 1197
Subject: Re: Overheating (was Re: Compression algo's for FPGA's)
From: billms@corp.mot.com (Bill Mangione-Smith)
Date: 12 May 1995 16:27:34 GMT
Links: << >>  << T >>  << A >>
   >>>>> On 11 May 1995 15:23:57 GMT, billms@corp.mot.com (Bill Mangione-Smith) said:
   BMS> A better example of good engineering would be to remove the threat.
   BMS> *Most* of my digital parts don't flame-out, why should we tolerate it
   BMS> of FPGAs?

   It is extremely difficult to remove the threat when you are using the
   FPGAs in a reconfigurable system. In a static system where all of the
   bitstreams are fixed, there isn't much of a problem. However, when you
   build a system where it is the intent to allow the user to reconfigure
   the resources, I see no way to completely remove the threat. Even if
   you check to make sure the bitstream is legal, you cannot guarantee
   that the user won't download the wrong bitfile and cause contention
   between connected components.

Ok, we are zeroing in on the issue, which appears to just be my inexperience
with the parts and misunderstanding of the comments made here.  Certainly
a device can be configured to cause problems with other components, and 
there's not much that can be done to solve that within the FPGA.  Thats
the cost of flexibility.

The second issue is on chip faults.  It would be nice if a device could 
not be configured in a way that would burn it up, under the condition that
it isn't connected to anything but power, ground, and the configuration 
system.  From the discussion, I was assuming this does in fact show up as
a problem.  So is my error in reading the posts (i.e. it doesn't happen)
or in misunderstanding the flexibility needed on chip, which requires you
to have the ability to toast your parts.

   general systems, though.  GigaOp's approach does not add that much in
   the way of cost, given the cost of everything else. 

Thats the worlds apart issue.  I'm used to embedded systems where $7
dollars in parts and 1/2 sq inch on the board is incredibly expensive.
We'd like to apply FPGA technology to a few problems in this market, and
the cost of that functionality is likely to drop sufficiently to make
this possible sometime in the near future.

Bill


Article: 1198
Subject: Re: Overheating (was Re: Compression algo's for FPGA's)
From: hutch@timp.byu.edu (Brad Hutchings)
Date: 12 May 95 09:37:53
Links: << >>  << T >>  << A >>
RA> In the case of xilinx, you don't have to worry about these problems, since
RA> xilinx doesn't support partial reconfiguratiion!

I wasn't even attempting to address partial reconfiguration. Its more
complex but the basic problems are similar.  My past postings have
only dealt with much simpler global reconfiguration approaches.

As I said earlier, you have to worry about potential hardware damage
anytime the hardware is going to get reconfigured as a part of normal
operation. It matters little whether you are partially reconfiguring
the system or not. It also doesn't really matter if there are multiple
FPGAs in the system or not. The point is that, there is really no way
to keep an applications programmer (on Splash-II, for example) from
downloading an incorrect --but legal-- bitfile and causing some damage.
And, if the system configurations are always getting modified (as they
are in reconfigured systems), there are just that many more opportunities
for problems.

Here are a couple of simple examples.

1. Consider a system consisting of a single FPGA device and one memory
device.  If the memory and the FPGA simultaneously drive say, a 32-bit
data bus, there is probably going to be some heat. How can this
happen? Well, it could be that the user downloaded the correct
bit-file but has a a timing error in the design. Because these events
are transient, they are not as severe as the case where the user
downloads an incorrect bit-file, a multiplier for example. In the
multiplier case, it may just happen that the outputs of the multiplier
drive the memory control lines and data lines such that that the
32-bit data bus is constantly driven from both sources. As this is not
as transient of an event, this heat-producing situation may continue
long enough to damage some hardware, unless you detect the excess heat
and shut the thing down (in some cases you may be able to detect
excess current instead of heat).

2. Consider a larger system, say Splash-II. In one of our MS theses,
the student created a design that consisted of several FPGAs. Each of
the FPGAs assumed a specific direction of data transmission. Some went
right-to-left, others went left-to-right (Splash-II is organized as a
linear array) All this works fine, but lets say that the student
accidentally loads his bit-files into the wrong devices (this is
easier than you think). In the worst case, you will see that two
adjacent devices will be simultaneously sourcing data onto the same
wires, and some excess heat will be produced with potential device
damage.

The truth is, we have blown up precious few FPGA parts in our lab.  We
have been running applications on our Splash-II for over 6 months now
and have had no problems. All of our FPGA-based systems have turned
out to be pretty durable. However, I do believe in being careful
though and have taught all of the students here to be responsibly
paranoid :-).


 


--
            Brad L. Hutchings - (801) 378-2667 - hutch@ee.byu.edu 
Brigham Young University - Electrical Eng. Dept. - 459 CB - Provo, UT 84602
                       Reconfigurable Logic Laboratory



Article: 1199
Subject: Re: Overheating (was Re: Compression algo's for FPGA's)
From: matthew@rd.bbc.co.uk (Matthew Marks)
Date: Fri, 12 May 1995 16:44:39 GMT
Links: << >>  << T >>  << A >>
randraka@ids.net wrote:
: Many of you responding to this thread have mentioned Xilinx.  In a single
: Xilinx, this is normally NOT a problem, even if the part is being reloaded with
: new programs during the course of its operation.  The heat problems Brad refers
: to are a result of partial reconfiguration where a portion of the device
: remains running with its original programming while another portion is
: reprogrammed (yes there are devices out there that support this mode).

I think you may be giving people a false sense of security here.  A 3000 Xilinx
will happily accept a random bitstream and then come up full of internal
short circuits.  The only thing it detects is if you forget to plug the
configuation ROM in (for instance), when it will wait for ever.  So the thing
can blow up either if you've made a mistake with your CAD and the wrong IO
pins are programmed, or if corruption has occurred to the bitstream (such as a 
failing EPROM might introduce, methinks).

Matthew  matthew@rd.bbc.co.uk  My opinions, not Auntie's.
In that
: case, as he mentions, the user must be extremely careful about the output
: connections from every cell during the course of partial reconfiguration.  Even
: if the circuit is connected properly at the end of the reconfig, you can get
: momentary contention during the process depending on the order that the cell
: functions are changed.  
:  
: In the case of xilinx, you don't have to worry about these problems, since
: xilinx doesn't support partial reconfiguratiion!  Of course you will also have
: considerable challenges in trying to do what Brad is doing without the ability
: to partially reconfigure.  The closest you come with Xilinx is to use a tiled
: approach where a system consisting of multiple xilinx can be partially
: reconfigured by changing the programs in a subset of the xilinx chips.  Here,
: you can run into the problem at a higher level (only at the I/O of the Xilinx
: chips).  That is what Brad was referring to when he mentioned the resistors
: between devices. 
:  
: Hope this clears some of the apparent confusion.

: -Ray Andraka
: Chairman, the Andraka Consulting Group
: 401/884-7930    FAX 401/884-7950
: email randraka@ids.net
:  
: The Andraka Consulting Group is a digital hardware design firm specializing in
: obtaining the maximum performance from FPGAs.  Services include complete
: design, development, simulation, and integration of these devices and the
: surrounding circuits.  We also evaluate, troubleshoot, and improve existing
: designs.  Please call or write for a free brochure.





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2009JanFebMarAprMayJunJulAugSepOctNovDec2009
2010JanFebMarAprMayJunJulAugSepOctNovDec2010
2011JanFebMarAprMayJunJulAugSepOctNovDec2011
2012JanFebMarAprMayJunJulAugSepOctNovDec2012
2013JanFebMarAprMayJunJulAugSepOctNovDec2013
2014JanFebMarAprMayJunJulAugSepOctNovDec2014
2015JanFebMarAprMayJunJulAugSepOctNovDec2015
2016JanFebMarAprMayJunJulAugSepOctNovDec2016
2017JanFebMarApr2017

Authors:A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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