Site Home   Archive Home   FAQ Home   How to search the Archive   How to Navigate the Archive   
Compare FPGA features and resources   

Threads starting:
1994JulAugSepOctNovDec1994
1995JanFebMarAprMayJunJulAugSepOctNovDec1995
1996JanFebMarAprMayJunJulAugSepOctNovDec1996
1997JanFebMarAprMayJunJulAugSepOctNovDec1997
1998JanFebMarAprMayJunJulAugSepOctNovDec1998
1999JanFebMarAprMayJunJulAugSepOctNovDec1999
2000JanFebMarAprMayJunJulAugSepOctNovDec2000
2001JanFebMarAprMayJunJulAugSepOctNovDec2001
2002JanFebMarAprMayJunJulAugSepOctNovDec2002
2003JanFebMarAprMayJunJulAugSepOctNovDec2003
2004JanFebMarAprMayJunJulAugSepOctNovDec2004
2005JanFebMarAprMayJunJulAugSepOctNovDec2005
2006JanFebMarAprMayJunJulAugSepOctNovDec2006
2007JanFebMarAprMayJunJulAugSepOctNovDec2007
2008JanFebMarAprMayJunJulAugSepOctNovDec2008
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

Custom Search

Messages from 58675

Article: 58675
Subject: Re: Multi Cycle path and False paths
From: snandap@hotmail.com (Prasanna)
Date: 30 Jul 2003 11:53:39 -0700
Links: << >>  << T >>  << A >>
"hrwieuyriwru" <jkshdfkjhskdjfksfksd@dfuosdf.com> wrote in message news:<WyHVa.696$il2.75461696@newssvr21.news.prodigy.com>...
> "Subroto Datta" <sdatta@altera.com> wrote in message
> news:qXuUa.3036$NV3.1143@newssvr31.news.prodigy.com...
> > Multicycle paths are paths between registers that intentionally take more
> > than one clock cycle to become stable. For example a register may need to
> > trigger a signal every second or third rising clock edge.
> >
> > A False path is any path that is not relevant to a circuit's operation.
> >
> > A good description of both multicycle and false paths can be found in the
> > following Timing Analysis App Note:
> >
> > http://www.altera.com/literature/an/an123.pdf
> >
> > Subroto Datta
> > Altera Corp.
> 
> From a conceptual standpoint, these definitions are mostly correct.
> But be aware that different CAD-tool vendors (Synopsys, Cadence,
> etc.) may treat the *operational* meanings of false-path differently..
> 
> In Synopsys's case, their application manuals have clear
> examples when to use 'set_disable_timing' versus 'set_false_path.'
> The problem with set_false_path is that it can (unintentionally)
> affect more than just timing-constraints.
> 
> >
> >
> >
> > "LIJO" <lijo_eceNOSPAM@hotmail.com> wrote in message
> > news:bftlvd$iao78$1@ID-159866.news.uni-berlin.de...
> > > Hi,
> > > Can anyone tell me  what is Multi Cycle path and False path?
> > >
> > > thanks
> > > Lijo
> > >
> > >
> > >
> > >
> >
> >
> >

Here are some examples I can think of.

Lets say you have a mode bit that you use in your logic and you know
some paths specifically do not exist when the core is not in that
mode, that becomes a false path.

Lets say, you do a complex logic such as a CRC and find that your
final CRC evaluation takes more than one clock cycle (based on byte
enables) and cannot meet the speed requirements. You can pipeline the
data and calculate final CRC in multiple clock cycles.

Open to learn more :-)

Article: 58676
Subject: Re: Downloading into XCV600
From: Mike Treseler <mike.treseler@flukenetworks.com>
Date: Wed, 30 Jul 2003 11:55:21 -0700
Links: << >>  << T >>  << A >>
Isaac wrote:

> 1. Do I have to define different input / output signal so that every
> BLOCK has different signal names from each other and than use port map
> and component decelartion in top *.vhd file to accopmlish the task.

Read up on the VHDL generate statement.
Here's a related example:

http://groups.google.com/groups?q=generate+add_1_bit

  -- Mike Treseler


Article: 58677
Subject: Re: Parallel Port EPP in FPGA
From: "Andras Tantos" <andras_tantos@tantos.yahoo.com>
Date: Wed, 30 Jul 2003 12:00:53 -0700
Links: << >>  << T >>  << A >>

> > I had the same experience: the PC parallel port HW wouldn't switch into
EPP
> > mode without the proper negotiation. You will stay in SPP mode on the SW
> > side, though you can emulate the EPP protocoll from SW. And yes, it's
slow.
> >
> > Andras Tantos
>
> Were you able to implement the proper negotiation and avoid staying in
> SPP? If so what do you recommend?

Unfortunately no, due to lack of time. I also had the poblem that I
configured my FPGA through the same parallel port so I'm not sure if I could
re-negoiate the protocol after configuration in my design at all.

Andras Tantos



Article: 58678
Subject: Altera-to-Xilinx IO
From: prashantj@usa.net (Prashant)
Date: 30 Jul 2003 12:11:25 -0700
Links: << >>  << T >>  << A >>
Hi,

I'm trying to interface a Xilinx board (XC2V6000) with an Altera board
(Apex20K1500E). The Xilinx board IO is at 1.8V while the Altera board
IO is at 3.3V. Now if the Altera Vccint is tied to 1.8V, the Altera
part can take inputs at 1.8, 2.5 and 3.3 V. Meanwhile, the output
voltage of the Altera part is fixed to the Vccio voltage (3.3V on my
Altera board). But it doesnt look like the Xilinx part can take the 3
different input voltage levels if its Vcco is tied to 1.8V. Is this
true ? If so, I would be surprised that Xilinx doesnt have a feature
that Altera has.

So, I can take inputs from the Xilinx board, but cant provide 3.3V
outputs from the Altera board to the Xilinx board. Any solutions ?

Thanks,
Prashant

Article: 58679
Subject: tri-State buffer troubles ...
From: Eric <nobody@spamcop.net>
Date: Wed, 30 Jul 2003 15:58:16 -0400
Links: << >>  << T >>  << A >>
Hi,

I'm designing a bus oriented processor peripheral chip using a XC2S100 / webpack 5.2 SP3

It went well until the chip was filled about 50% then strange trouble with the tristate buffers started to appear,
leading to strange behaviour.
I use these tri-state buffers only in the top level schematic diagram.


Here are the symptoms :
-------------------------

=> ECS gives me this warning :
Warning: Net "CPU_DI(15)" is connected to too many sources pins and/or IO ports. A Wired Or connection will be used.

"CPU_DI" is a 16 bits bus with 4x16 bits sources, 4x8 bits sources on the upper half and 4x8 bits sources on the
lower half, all controlled using BUFE buffers.

=> When compiling the design, I get the following warning/error messages :

WARNING:Xst:528 - Multi-source in Unit <testio> on signal <cpu_di<15>> not replaced by logic
Sources are: xlxi_492:o<15>, xlxi_895:o<15>, xlxi_340:o<7>, xlxi_849:do<15>
( ... same message for all 16 pins ... )
ERROR:Xst:415 - Synthesis failed

=> In the new RTL schematic viewer :

I found that the lower part of the bus have been split in two seemingly unrelated entities.
In the RTL schematics, the 16 bit connections refer to CPU_DI(15:0), while the 8 bits connections refer to a bus
named "_n0131(7:0)" (this name does not appear anywhere in the original schematic diagram, nor in the ".vhf" file).


-------------------------

I'm a bit confused by it ...

What exactly makes ECS "think" that my bus is connected to "too many sources" ?
how many sources can be connected to a bus through BUFE/BUFT buffers before this message appears ?
Is it related to the way I control the BUFE's "Enable" input ?

answer database #14264 says "in most cases, XST is able to determine when multiple drivers are illegal".
How does it determine it ?
Are they specific rules the tool expects us to follow when designing the mutually exclusive BUFE "enable" signals ?

-------------------------

A solution could be to convert it all to multiplexers, but my goal with tri-state buffers was to reduce ressource
usage. However, as you might guess, I would like to avoid this and learn how to properly use tri-state buffers in
Spartan II.

Any help would be appreciated,

Eric.


Article: 58680
Subject: Re: Altera-to-Xilinx IO 3.3V -> 1.8V
From: Austin Lesea <Austin.Lesea@xilinx.com>
Date: Wed, 30 Jul 2003 13:39:10 -0700
Links: << >>  << T >>  << A >>
Prashant,

The reason why we "do not have this feature" is that the IO ESD cell
required for that feature is a non standard cell design (ie not a foundry
supported standard ESD IO cell).  That said, there is nothing wrong with
that (it has its advantages).  But, a few years ago we decided that rather
than be responsible for our ESD, we would prefer to use the foundry
specific (and guaranteed) ESD solution.  That lowers the capacitance
(makes it faster) and has other advantages as well.  Not to mention the
ESD performance is wonderful.  Now designing your own ESD is just fine,
but everytime there is any little process change, you have to re-qualify
the ESD protection performance.  The area is also larger.  And guess who
pays for area?

Lets see:  performance, worse; ESD, worse; Area, larger; can be driven
with voltages >> Vcco.

Our features: better performance, better ESD, smaller area, Vin < Vcco.

To be compatible with a driver that pulls to a voltage higher than Vcco,
you need some series resistance to drop the voltage (and limit the
current).

We recommend not sourcing more than 10 mA per input (for signal integrity
reasons, the diodes will handle ampere transients).

Their part also allows for lower IO voltages, by using 1.8V on the bank
that has the drivers in it, so that would be the prefered approach.  Or
you can up the Vcco voltage on one of our banks to 3.3V.

Austin

Prashant wrote:

> Hi,
>
> I'm trying to interface a Xilinx board (XC2V6000) with an Altera board
> (Apex20K1500E). The Xilinx board IO is at 1.8V while the Altera board
> IO is at 3.3V. Now if the Altera Vccint is tied to 1.8V, the Altera
> part can take inputs at 1.8, 2.5 and 3.3 V. Meanwhile, the output
> voltage of the Altera part is fixed to the Vccio voltage (3.3V on my
> Altera board). But it doesnt look like the Xilinx part can take the 3
> different input voltage levels if its Vcco is tied to 1.8V. Is this
> true ? If so, I would be surprised that Xilinx doesnt have a feature
> that Altera has.
>
> So, I can take inputs from the Xilinx board, but cant provide 3.3V
> outputs from the Altera board to the Xilinx board. Any solutions ?
>
> Thanks,
> Prashant


Article: 58681
Subject: AREA_GROUP constraint for Xilinx FPGAs
From: aman_78in@yahoo.com (Aman Gayasen)
Date: 30 Jul 2003 14:56:47 -0700
Links: << >>  << T >>  << A >>
Hi,
 I am trying to map some modules in my design into different regions
on an
FPGA (XC2V250). I also wish that the AREA_GROUP that is designated for
a particular instance does NOT contain any other logic.
 Is there a way to do this?

 I have tried using the AREA_GROUP constraint, but it does not prevent
ungrouped logic from being mapped into the region assigned to an
area-group.
 I looked through the Constraints guide that Xilinx provides. It says
that such a behavior can be obtained for modular design flow. Does
that mean I will need to unnecessarily use a modular design flow
(although I have all the module descriptions ready with me, and my
design is not really very big).

 Please tell me if there is a simpler way.

regards,
Aman

Article: 58682
Subject: Re: Altera-to-Xilinx IO 3.3V -> 1.8V
From: "Pete Fraser" <pete@rgb.com>
Date: Wed, 30 Jul 2003 15:29:20 -0700
Links: << >>  << T >>  << A >>

"Austin Lesea" <Austin.Lesea@xilinx.com> wrote in message
news:3F282CEE.521DD3E1@xilinx.com...

> The reason why we "do not have this feature" is that the IO ESD cell
> required for that feature is a non standard cell design (ie not a foundry
> supported standard ESD IO cell).

Thanks for the explanation. It's the first time I've
heard it in adequate detail.

However, you should know that it has cost you
at least two designs that I know of.



Article: 58683
Subject: Mentor Hyperlynx IBIS simulator (was Re: Spartan IIE max pin switching)
From: Eric Smith <eric-no-spam-for-me@brouhaha.com>
Date: 30 Jul 2003 15:36:33 -0700
Links: << >>  << T >>  << A >>
Austin Lesea <Austin.Lesea@xilinx.com> writes:
> Hyperlynx handles connectors, daughter cards, etc.  It just gets complex, which is not so much of a problem, as it is reality.

The web site and data sheet look great.  But what input formats for the
PCB design do they support?  Any open formats?  I use Eagle, which isn't
listed.  I wouldn't mind writing a translator to some other open format
if necessary, but if they only support proprietary formats it won't do
me any good.

And what does a single-user license for Hyperlynx EXT cost?

Article: 58684
Subject: Re: Multi Cycle path and False paths
From: "Glen Herrmannsfeldt" <gah@ugcs.caltech.edu>
Date: Wed, 30 Jul 2003 22:46:40 GMT
Links: << >>  << T >>  << A >>

"Ray Cheung" <cccheung@cse.cuhk.edu.hk> wrote in message
news:1059236649.547176@eng-ser4...
> There is a short and good example on multi-cycle path. Thanks.
> http://www.saros.co.uk/hdlsolutions/appsnotes/leonardo/SAN001.pdf

That does seem to be a good explanation.

I was almost thinking that they were still going to latch the data every
clock cycle, and depend on the delay through the logic.
That is, the delay through the combinatorial logic was guaranteed to be more
than three clock cycles, and less than four, with new data entered every
clock cycle, and results latched every clock cycle.

It is my understanding that some of Cray's machines did something like that.
There are descriptions of PC board traces intentionally longer to delay
signals.  I don't believe, though, that it would work well with FPGA's.  It
only works if you know the gate delay very accurately.

Many intel processors used dynamic logic, which I believe is registers that
store data in capacitors such that they have a minimum clock frequency.

-- glen



Article: 58685
Subject: Re: Altera-to-Xilinx IO 3.3V -> 1.8V
From: Austin Lesea <Austin.Lesea@xilinx.com>
Date: Wed, 30 Jul 2003 16:08:14 -0700
Links: << >>  << T >>  << A >>
Pete,

We win some, we lose some. You never know what "feature" (or latent bug) will
be the deciding factor.

But thanks for the feedback.  I was well aware of the issue and the tradeoffs.
If folks want that 5V input tolerance without limiting resistors, they can
still buy Xilinx and use Spartan II, or Virtex.

Austin

Pete Fraser wrote:

> "Austin Lesea" <Austin.Lesea@xilinx.com> wrote in message
> news:3F282CEE.521DD3E1@xilinx.com...
>
> > The reason why we "do not have this feature" is that the IO ESD cell
> > required for that feature is a non standard cell design (ie not a foundry
> > supported standard ESD IO cell).
>
> Thanks for the explanation. It's the first time I've
> heard it in adequate detail.
>
> However, you should know that it has cost you
> at least two designs that I know of.


Article: 58686
Subject: Re: Mentor Hyperlynx IBIS simulator (was Re: Spartan IIE max pin
From: Austin Lesea <Austin.Lesea@xilinx.com>
Date: Wed, 30 Jul 2003 16:09:40 -0700
Links: << >>  << T >>  << A >>
Eric,

All these questions are best answered by Mentor/HyperLynx.

I just don't know all of those details

I think we can extract from the Gerber files, but I am not sure.

Austin

Eric Smith wrote:

> Austin Lesea <Austin.Lesea@xilinx.com> writes:
> > Hyperlynx handles connectors, daughter cards, etc.  It just gets complex, which is not so much of a problem, as it is reality.
>
> The web site and data sheet look great.  But what input formats for the
> PCB design do they support?  Any open formats?  I use Eagle, which isn't
> listed.  I wouldn't mind writing a translator to some other open format
> if necessary, but if they only support proprietary formats it won't do
> me any good.
>
> And what does a single-user license for Hyperlynx EXT cost?


Article: 58687
Subject: Re: Pricing question....
From: "Paul Leventis" <paul.leventis@utoronto.ca>
Date: Wed, 30 Jul 2003 23:54:40 GMT
Links: << >>  << T >>  << A >>
> One additional source of info would be to get the fab costs for the
> 8"/12" wafers from say TSMC or UMC and try to figure the production
> costs of your FPGA and possibly your own design committed to an ASIC
> directly for comparison.
>
> I am not saying this is easy...

You can say that again -- I don't think it's possible for anyone outside the
operations/product engineering groups of an FPGA company to compute the cost
of FPGA fabrication.  You need to know (a) wafer prices (b) mask costs
(ammortized over # of chips produced) (c) defect density vs. demand over
product lifetime (d) die sizes (e) suceptability to defects (f) repair rates
(for Altera parts w/redundancy) (e) development/support/software costs
(ammortized over products sold) etc.  And because big FPGA manufacturers are
some of the largest fab customers/partners, I'd guess they don't pay list
price...

Regards,

- Paul Leventis
Altera Corp.



Article: 58688
Subject: Re: ALTERA Byte BlasterII
From: Marc Guardiani <marc@guardiani.com>
Date: Wed, 30 Jul 2003 20:44:42 -0400
Links: << >>  << T >>  << A >>
Go to Altera's web site or do a google search.


Lev Razamat wrote:
> If anybody have a chematic of the ALTERA Byte Blaster II. Or if anybody can
> send me link to this schematic
> 
> Thanks in advance
> 
> Lev
> 
> 

-- 


Marc Guardiani

To reply directly to me, use the address given below. The domain name is 
phonetic.
fpgaee81-at-eff-why-eye-dot-net


Article: 58689
Subject: Re: tri-State buffer troubles ...
From: Marc Guardiani <marc@guardiani.com>
Date: Wed, 30 Jul 2003 20:49:21 -0400
Links: << >>  << T >>  << A >>
Since you're doing schematics with tristate buffers in them, you need to 
consider a bug in 5.x that will not be fixed until 6.1i. Iterated 
instances of IOBUFs and BUFTs are processed incorrectly. A dummy net is 
created then not connected to the buffer. The only work-around is to 
hand edit the HDL output of the synthesized schematic.


Eric wrote:
> Hi,
> 
> I'm designing a bus oriented processor peripheral chip using a XC2S100 / 
> webpack 5.2 SP3
> 
> It went well until the chip was filled about 50% then strange trouble 
> with the tristate buffers started to appear,
> leading to strange behaviour.
> I use these tri-state buffers only in the top level schematic diagram.
> 
> 
> Here are the symptoms :
> -------------------------
> 
> => ECS gives me this warning :
> Warning: Net "CPU_DI(15)" is connected to too many sources pins and/or 
> IO ports. A Wired Or connection will be used.
> 
> "CPU_DI" is a 16 bits bus with 4x16 bits sources, 4x8 bits sources on 
> the upper half and 4x8 bits sources on the
> lower half, all controlled using BUFE buffers.
> 
> => When compiling the design, I get the following warning/error messages :
> 
> WARNING:Xst:528 - Multi-source in Unit <testio> on signal <cpu_di<15>> 
> not replaced by logic
> Sources are: xlxi_492:o<15>, xlxi_895:o<15>, xlxi_340:o<7>, xlxi_849:do<15>
> ( ... same message for all 16 pins ... )
> ERROR:Xst:415 - Synthesis failed
> 
> => In the new RTL schematic viewer :
> 
> I found that the lower part of the bus have been split in two seemingly 
> unrelated entities.
> In the RTL schematics, the 16 bit connections refer to CPU_DI(15:0), 
> while the 8 bits connections refer to a bus
> named "_n0131(7:0)" (this name does not appear anywhere in the original 
> schematic diagram, nor in the ".vhf" file).
> 
> 
> -------------------------
> 
> I'm a bit confused by it ...
> 
> What exactly makes ECS "think" that my bus is connected to "too many 
> sources" ?
> how many sources can be connected to a bus through BUFE/BUFT buffers 
> before this message appears ?
> Is it related to the way I control the BUFE's "Enable" input ?
> 
> answer database #14264 says "in most cases, XST is able to determine 
> when multiple drivers are illegal".
> How does it determine it ?
> Are they specific rules the tool expects us to follow when designing the 
> mutually exclusive BUFE "enable" signals ?
> 
> -------------------------
> 
> A solution could be to convert it all to multiplexers, but my goal with 
> tri-state buffers was to reduce ressource
> usage. However, as you might guess, I would like to avoid this and learn 
> how to properly use tri-state buffers in
> Spartan II.
> 
> Any help would be appreciated,
> 
> Eric.
> 

-- 


Marc Guardiani

To reply directly to me, use the address given below. The domain name is 
phonetic.
fpgaee81-at-eff-why-eye-dot-net


Article: 58690
Subject: Re: binary to BCD assistance
From: "Glen Herrmannsfeldt" <gah@ugcs.caltech.edu>
Date: Thu, 31 Jul 2003 01:35:45 GMT
Links: << >>  << T >>  << A >>

"Jason Berringer" <look_at_bottom_of@email.com> wrote in message
news:IlGVa.3393$mv6.617644@news20.bellglobal.com...
> Here is the code (after my text) instead of an attachment in case others
> cannot read it.
>
> It takes (or should take) 20 to 21 clock cycles to get the data from the
> input to the output. I put a few numbers through the simulation the only
> correct values are 0 and 1, all other tested were incorrect. I'm pretty
sure
> it's a simple error that I'm not catching, I just can't see it at present.
> Most of the stuff that I have done has been a bit more simple than this.
The
> algorithm works from a sample I've seen (no code just an explanation).
Start
> by shifting the most significant bit of your binary number into the least
> significant bit of your "units" bcd value, when the number in the "units"
> value is 5 or greater add 3 to it. Shift again, if the value is 5 or
greater
> add 3 to it, the values will continue to spill over to the "tens",
> "hundreds", "thousands", etc. You must add 3 to each of the bcd digits if
> any is five or greater, by the last shift (same number of shifts as your
> input binary value (in my case 20 bits)) you'll have the bcd
representation.
> The example I mentioned above was for a microcontroller.

As I said, I read Verilog much better than VHDL.  I didn't even notice the
loop yesterday, which is why I didn't think it was complicated enough.  OK,
thought for today:



(snip)

>  elsif rising_edge(clk) then

Does the following generate a gated clock?

>   if shift_en_s = '1' then

The following statement must be done before the rest.  While simulators may
execute them in order, synthesized logic tends to execute them all at the
same time.

>    bcd_value := bcd_value(22 downto 0) & ser_out_s;
>    bcd_out_s <= bcd_value;

Does this generate a gated clock?  Can you do it in traditional synchronous
logic form, where either the previous contents, or the contents with "0011"
added are loaded back in?  (Also with the shift_en_s enable.)

>     if bcd_value(3 downto 0) >= "0101" then
>      bcd_value(3 downto 0) := bcd_value(3 downto 0) + "0011";
>     end if;

(snip)

Gated clocks are especially hard in FPGA's.

-- glen



Article: 58691
Subject: Re: PLL / DPLL phase question
From: Thad Smith <ThadSmith@acm.org>
Date: Wed, 30 Jul 2003 19:45:56 -0600
Links: << >>  << T >>  << A >>
Thad Smith wrote:

I'm following up my own post for a correction.

> Assuming that the DAC is updated once each cycle of the output
> frequency, you want your frequency to be within f (1 +- 1/3600), which
> would generate the maximum phase error, assuming that the phase was
> exactly matched at the beginning.  That suggests that you want at least
> a 12-bit converter.

12 bits should be sufficient for the full scale frequency.  Since the OP said he needed to
track 1 to 50 Hz with 0.1 degree max phase error, he will need an additional 6 bits to get
the required resolution at the low end (1 Hz).  Note that 18 bits of accuracy aren't
needed -- only 18 bits of resolution, because of the feedback.  The resolution could be
achieved with 2 10 bit or 12 bit converters.

> If you did external filtering, you could use fewer bits and toggle the
> DAC setting more frequently such that the average voltage is for the
> correct frequency.

This is still true and could be used instead of another converter.

Thad

Article: 58692
Subject: Re: Mentor Hyperlynx IBIS simulator (was Re: Spartan IIE max pin switching)
From: Eric Smith <eric-no-spam-for-me@brouhaha.com>
Date: 30 Jul 2003 19:27:09 -0700
Links: << >>  << T >>  << A >>
Austin Lesea <Austin.Lesea@xilinx.com> writes:
> All these questions are best answered by Mentor/HyperLynx.

Sure.  I was hoping someone might email me some rough idea on the price
before I waste a bunch of time trying to pry useful information loose
from a salesgoon.  Lord knows that all manner of unspeakable disasters
would occur if companies actually put content like that on their web
sites.



Article: 58693
Subject: Re: PLL / DPLL phase question
From: Andrew Paule <lsboogy@qwest.net>
Date: Wed, 30 Jul 2003 21:29:04 -0500
Links: << >>  << T >>  << A >>
Thad -

sounds good in theory - but there has never been a 12 bit DAC with 12 
bits of reality - the LSB is junk with power supply noise and 
non-linearity.  The 12 bit DACs are really capable of 11 - 11.3 bits 
with GOOD (excellent) gound planes and linear regulators and a cold 
plate for temperature stability.

The phase error means that his load into the m and n integer will not do 
well in this application - they only increment on cross.  I would 
suggest going to a full digitally done output using the dac and 
integrating it a little (time constant ~ 1/2 the update rate).  The 
phase error budget here will kill him .

Andrew
Thad Smith wrote:

>Thad Smith wrote:
>
>I'm following up my own post for a correction.
>
>  
>
>>Assuming that the DAC is updated once each cycle of the output
>>frequency, you want your frequency to be within f (1 +- 1/3600), which
>>would generate the maximum phase error, assuming that the phase was
>>exactly matched at the beginning.  That suggests that you want at least
>>a 12-bit converter.
>>    
>>
>
>12 bits should be sufficient for the full scale frequency.  Since the OP said he needed to
>track 1 to 50 Hz with 0.1 degree max phase error, he will need an additional 6 bits to get
>the required resolution at the low end (1 Hz).  Note that 18 bits of accuracy aren't
>needed -- only 18 bits of resolution, because of the feedback.  The resolution could be
>achieved with 2 10 bit or 12 bit converters.
>
>  
>
>>If you did external filtering, you could use fewer bits and toggle the
>>DAC setting more frequently such that the average voltage is for the
>>correct frequency.
>>    
>>
>
>This is still true and could be used instead of another converter.
>
>Thad
>  
>


Article: 58694
Subject: DDS question. How to generate a square from a sine wave?
From: jaxlau@yahoo.com (Jacques athow)
Date: 30 Jul 2003 21:09:43 -0700
Links: << >>  << T >>  << A >>
I have a project that needs a 21.48MHZ clock input. But the problem is
that I dont have that type of oscillator. As the project is going to
be in an large FPGA , is it possible to generate using coregen and a
40MHZ square source(the FPGA clock), a dds with adequate resolution
and that at a certain phase increment, would in turn generate the
21.48MHZ needed but as a sinusoid.

Now, in order to complete the design, the signal would remain in the
digital domain and pass through some clipping logic, which would give
a '1' when the sine value is greater than an arbritrary index. At the
output of this block, we would theoretically have a square wave. The
only inconvenience is that the generated square wave would be one that
doesn't possess a 50% duty cycle.

Could we use the available DLL to reconstruct the clock, based from
the just created pseudo clock from the DDS?

The tool used is coregen and we have a virtex 2 platform.
I would really appreciate some clues about this idea.

Thanks.
Jac

Article: 58695
Subject: Re: apex20ke library and simulation
From: "Subroto Datta" <sdatta@altera.com>
Date: Thu, 31 Jul 2003 04:12:56 GMT
Links: << >>  << T >>  << A >>
Jean-Luc,

    To simulate, either do a functional sim prior to synthesis or do a
timing simulation using the VHDL/Verilog netlist generated after place and
route.A step by step description can be found in:
http://www.altera.com/support/software/nativelink/simulation/modelsim/eda_vi
ew_using_msim.html

- Subroto Datta
Altera Corp.


"Jean-Luc" <nagel@computer.org> wrote in message
news:b5a538f6.0307300636.2e61513b@posting.google.com...
> Hello,
>
> I am designing a circuit for an Apex20ke FPGA with Synopsys v2001.8
> and Quartus2.
> After compilation I want to simulate the design in ModelSim 5.5e.
> Therefore I saved the current design using:
>
> write -format v -hierarchy -output top.v
> write_sdf -version 2.1 top.sdf
>
> In ModelSim I could compile fine the verilog netlist but could not
> load it due to an enormous number of errors such as:
>
> #       Region: :top:I0:I1
> #         Searched libraries:
> #             work
> # ERROR: /pe_users/nagel/vhdl/smartcam/synopsys_linux/top.v(40686):
> Instantiation of 'ATBL_1' failed (design unit not found).
>
> Now I included a number of libraries from Altera in my work library:
>
> lpm
> altera_mf
> apex20ke
>
> But these ATBL_* - that are in the apex20ke-3.db library (as reported
> by report_library) - are still not found...
>
> Any help would be highly appreciated !
>
> Thank you,
> Jean-Luc



Article: 58696
Subject: Re: DDS question. How to generate a square from a sine wave?
From: Andrew Paule <lsboogy@qwest.net>
Date: Wed, 30 Jul 2003 23:26:37 -0500
Links: << >>  << T >>  << A >>
Hi Jacques:

I think putting a Fox or Epson type oscillator on would be cheaper (no 
gates burned) and quicker than doing this, might be a fun excercise, but 
you are going to have to implement external dacs for this one - I don't 
think that Xilinx is prepared to enter the analog world, and a dds with 
the resolution you need is going to require a couple of fast dacs.

Andrew

Jacques athow wrote:

>I have a project that needs a 21.48MHZ clock input. But the problem is
>that I dont have that type of oscillator. As the project is going to
>be in an large FPGA , is it possible to generate using coregen and a
>40MHZ square source(the FPGA clock), a dds with adequate resolution
>and that at a certain phase increment, would in turn generate the
>21.48MHZ needed but as a sinusoid.
>
>Now, in order to complete the design, the signal would remain in the
>digital domain and pass through some clipping logic, which would give
>a '1' when the sine value is greater than an arbritrary index. At the
>output of this block, we would theoretically have a square wave. The
>only inconvenience is that the generated square wave would be one that
>doesn't possess a 50% duty cycle.
>
>Could we use the available DLL to reconstruct the clock, based from
>the just created pseudo clock from the DDS?
>
>The tool used is coregen and we have a virtex 2 platform.
>I would really appreciate some clues about this idea.
>
>Thanks.
>Jac
>  
>


Article: 58697
Subject: Re: binary to BCD assistance
From: "Paul Leventis" <paul.leventis@utoronto.ca>
Date: Thu, 31 Jul 2003 05:50:19 GMT
Links: << >>  << T >>  << A >>
Hi Jason,

First off, that's a pretty cool little algorithm... had to prove to myself
that it worked.  Let digit = 5 + n, where n = 0..4.  We want new_digit =
(digit * 2 + shift_in) % 10 = (5 * 2 + n * 2 + shift_in) % 10 = n * 2 +
shift_in.  If we add three, and wrap around at 16 (since 4-bit
representation) then we get ((8 + n) * 2 + shift_in) % 16 = 2 * n +
shift_in.

I'm not sure that I've found the problem with your code, but there were a
number of stylistic issues and one suspicious fragment I figured I'd point
out.  I'll add a caveat that I haven't really coded up any VHDL in a year or
so, and prior to that my experience was mostly with structural VHDL.  And I
didn't have a compiler handy to try out my ideas.  So I imagine I'll find
out I'm wrong and learn something in the process!

(0) I think the first problem is a lack of comments... uncommented code is
always wrong :-)

(1) Process #3.  I hate variables.  Especially variables mixed with
signals... you must be very disciplined when using variables (I only use
them in for loops...).  So I honestly don't know what the code will
translate into, as you are assigning a value to variable, then assigning to
the variable to a signal, then changing the value of the variable.  I'm not
sure if the scheduled signal assignment occurs before or after the change in
variable value.  Also, I'm not sure that the variable turns into a register
(i.e. has memory) -- either way though, it's not what you want.  If it does
become a register, then have 2 24-bit registers (unnecsessary/may not work).
If you don't, then I don't know what will happen.  Regardless, I think you
want to first be adding three, THEN shifting.  There are two ways I can
think of restructuring this code into something that may work (see below).
The first replaces your variable with a signal that is computed
combinationally outside of the process.  The second is an attempt to still
use a variable, based on my limited understanding of this VHDL construct.
Note that neither requires the asynchronous condition (though I'm thinking
it may need an aclr for bcd_out_s...).

    if clk = '1' and clk'event then
        if load_data = '1' then
            bcd_out_s <= (OTHERS => '0');
        elsif shift_en_s = '1' then
            bcd_out_s <= bcd_out_modified_s(22 downto 0) & ser_out_s;
        end if;
    end if;
    ...
    bcd_out_modified_s(3 downto 0) <= bcd_out_s(3 downto 0) + "0011" when
bcd_value(3 downto 0) >= "0101" else bcd_value(3 downto 0);
    ...

or:

    if clk = '1' and clk'event then
        if load_data = '1' then
            bcd_out_s <= (OTHERS => '0');
        elsif shift_en_s = '1' then
            bcd_value := bcd_out_s;
            if bcd_value(3 downto 0) >= "0101" then
                bcd_value(3 downto 0) := bcd_value(3 downto 0) + "0011";
            end if;
            ...
            bcd_out_s <= bcd_value(22 downto 0) & ser_out_s;
        end if;
    end if;

I'm sure there are other ways to structure the code, and my way may add an
additional clock cycle or may need an extra bit in the register to work
right, but you get the idea.

(2) Process #3 makes use of an asynchronous clear on the condition of
load_data.  If you can do something synchronously instead of asynchronously,
you should.  There's no harm in putting another if clause in your clocked
portion of the process to cover the clear while loading case.

(3) Process #2.  You have two if statements, both of which affect bin_in_s:
    if load_data = '1' then
        bin_in_s <= data_in;
    end if;
    if shift_en_s = '1' then
        bin_in_s <= bin_in_s(18 downto 0) & '0';
    end if;
While legal, the interpretation (I think) is the same as the following code,
which is cleaner and thus less likely to be incorrect.  My experience is
whenever I try to be as smart as the compiler, I end up getting bitten by it
later...
    if shift_en_s = '1' then
        bin_in_s <= bin_in_s(18 downto 0) & '0';
    elsif load_data = '1' then
        bin_in_s <= data_in;
    end if;

(4) Process #1 & #4.  You are instantiating many more registers than
necessary.  You could get away without the data_out register (unless you
want to be able to process new data while some other chip takes its time
reading your result, which seems unlikely).  Also, you are inserting an
extra cycle of latency with your data_ready & data_out registers.  But there
should be nothing functionally wrong there.

(5) Your asynchronous reset may not be safe.  The topic of many discussions.
Not the problem you're having now I bet.

Good luck,

Paul Leventis



Article: 58698
Subject: Re: DDS question. How to generate a square from a sine wave?
From: hmurray@suespammers.org (Hal Murray)
Date: Thu, 31 Jul 2003 08:33:26 -0000
Links: << >>  << T >>  << A >>

>output of this block, we would theoretically have a square wave. The
>only inconvenience is that the generated square wave would be one that
>doesn't possess a 50% duty cycle.

Why wouldn't it be (close to) 50% duty cycle?  How close do you
need?

If you do the clipping with an inverter and AC couple the sine
wave to the input and bias the input with a big resistor feeding
back from the output, there is feedback on the bias that  wil
set the clipping level to make a 50% duty cycle output.

I'm not sure how well that works at high speeds.  It works fine
at anything that isn't pushing the inverter very hard.

-- 
The suespammers.org mail server is located in California.  So are all my
other mailboxes.  Please do not send unsolicited bulk e-mail or unsolicited
commercial e-mail to my suespammers.org address or any of my other addresses.
These are my opinions, not necessarily my employer's.  I hate spam.


Article: 58699
Subject: Re: VHDL Book Recommendations Please
From: Martin Thompson <martin.j.thompson@trw.com>
Date: 31 Jul 2003 10:43:08 +0100
Links: << >>  << T >>  << A >>
rickman <spamgoeshere4@yahoo.com> writes:

> Jonathan Bromley wrote:
> > Grin.
> > 
> > Find yourself a civilised editor with a block/column select and
> > fill facility.  On Windoze we generally use TextPad, which is
> > pretty goodand can be had in a free eval version if you don't
> > mind the nag screens:
> >   www.textpad.com
> > 
> > Or NEdit on Unix/Linux.
> 
> Just my two cents worth on the editor for comments.  CodeWright is not
> free, and it is not even real cheap the last time I looked, but it is
> very good.  It has programmable comment definitions for different file
> types.  It also have a generic "Prompted Slide In" and out.  This lets
> you insert or remove anything you want at the start of each line in a
> range.  The only thing you need to specify is the text to insert or
> remove.  
> 
> But I agree that it is down right silly that they don't have block
> comments in VHDL.  To quote Dr. Phil, "What were they thinking"?  
> 

I used to use CW, but IMHO the only editor to use for VHDL is Emacs
with its VHDL mode.  When I first switched, I worried about the
column-select being a bit wacky, but now I have VHDL-mode and the
other feature sof Emacs, I find that I don't actually need to column
select anymore.

I have heard good things about TurboWriter (which is stuff on top of
CodeWright) - see
http://www.saros.co.uk/index.htm?http%3A//www.saros.co.uk/hdlsolutions/products/index.shtml.

Just my tuppence!

Martin

-- 
martin.j.thompson@trw.com
TRW Conekt, Solihull, UK
http://www.trw.com/conekt



Site Home   Archive Home   FAQ Home   How to search the Archive   How to Navigate the Archive   
Compare FPGA features and resources   

Threads starting:
1994JulAugSepOctNovDec1994
1995JanFebMarAprMayJunJulAugSepOctNovDec1995
1996JanFebMarAprMayJunJulAugSepOctNovDec1996
1997JanFebMarAprMayJunJulAugSepOctNovDec1997
1998JanFebMarAprMayJunJulAugSepOctNovDec1998
1999JanFebMarAprMayJunJulAugSepOctNovDec1999
2000JanFebMarAprMayJunJulAugSepOctNovDec2000
2001JanFebMarAprMayJunJulAugSepOctNovDec2001
2002JanFebMarAprMayJunJulAugSepOctNovDec2002
2003JanFebMarAprMayJunJulAugSepOctNovDec2003
2004JanFebMarAprMayJunJulAugSepOctNovDec2004
2005JanFebMarAprMayJunJulAugSepOctNovDec2005
2006JanFebMarAprMayJunJulAugSepOctNovDec2006
2007JanFebMarAprMayJunJulAugSepOctNovDec2007
2008JanFebMarAprMayJunJulAugSepOctNovDec2008
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

Custom Search