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Messages from 32775

Article: 32775
Subject: Max+2 and multi-cycle timing analysis WAS: Altera ACEX
From: bob elkind <eteam@aracnet.com>
Date: Sun, 08 Jul 2001 18:31:49 -0700
Links: << >>  << T >>  << A >>
some possible solutions/workarounds:

1.  run timing analyser at 80/N MHz, to verify the multi-cycle paths;
and then run timing analyser at 80 MHz for the "normal" logic paths
(ignoring the spurious error reports for the multi-cycle paths).

2.  insert gratuitous pipeline registers in the multi-cycle paths, to make
the timing analyser happy.  If done with due clevernous, this may not
even affect logic cell utilisation at all (in Altera Flex devices).

3.  use the "ignore paths" facilities to guide the timing analyser.

You may need to declare the "result" registers of the multi-cycle paths
as "LCELL"s at the top level of hierarchy, to ensure that their
post-synthesis/post routing logical net names don't change from run
to run.

As far as I know, this is a problem common to most/all timing analysers,
with the design style you've chosen, and is not particularly peculiar to
MAX+II.  If I'm off base on this, please correct me!

It is my understanding that Quartus II will eventually supercede the
MAX+II tool (with perhaps excepting the 7Kx series of CPLDs),
over time.  Don't delete MAX+II for at least 6 months after you *think*
you're happy with Quartus II, as there will likely be weaknesses and
holes in the "coverage" of any given product family as each family is
first migrated from MAX+II to Quartus II.  Also, be prepared to max
out your PCs' memory (SDRAM) capacity, as Quartus II (like most
new generations of design tools) require more memory and more
compute power to deliver the same (or more) polish and sophistication
as the previous design tool generation.

Of course, I'm assuming that you haven't already tried these
solutions and run into brick walls already, in which case I
apologise for re-stating the obvioius...

-- Bob Elkind, the e-team  fpga/design consulting

Rick Collins wrote:

<quote deleted/skipped>

> We are working with the 10K parts on an existing board. We are
> trying to do a design with an 80 MHz clock where a portion of the
> circuit uses multiple clock cycles to process signals through
> combinatorial logic. It would appear that the MaxPlus II tools so not
> well support this type of design timing.
>
> The tool problems we have found are numerous. It is a bit like being in
> a maze and finding every path blocked. Our final approach is to simply
> constrain the entire design to 80 MHz, and manually examine all of the
> failure reports. The failures on single clock paths are fixed. The
> failures on multi-cycle paths are ignored. This is not fun as the
> failing paths change on each iteration of place and route. We call this
> the "whack-a-mole" approach. As you fix paths, other paths then fail.
> Once you have a working design, any change makes more moles pop up.
>
> One pleasant note is that the next release of the Quartus tool is
> supposed to support the 10K series. Quartus II has much better
> multi-cycle support. I don't know if they intend to support the 1K ACEX
> parts with Quartus II.
>
> --
>
> Rick "rickman" Collins
>
> rick.collins@XYarius.com
> Ignore the reply address. To email me use the above address with the XY
> removed.
>
> Arius - A Signal Processing Solutions Company
> Specializing in DSP and FPGA design      URL http://www.arius.com
> 4 King Ave                               301-682-7772 Voice
> Frederick, MD 21701-3110                 301-682-7666 FAX



Article: 32776
Subject: Re: Need some help using Synplify ... and also considering Xilinx Modular Flow
From: Muzaffer Kal <muzaffer@dspia.com>
Date: Mon, 09 Jul 2001 06:12:54 GMT
Links: << >>  << T >>  << A >>
On Mon, 09 Jul 2001 00:47:41 GMT, Ray Andraka <ray@andraka.com> wrote:
>Synplicity is not a simulator, so I am not sure what you mean by
>simulating two module netlists at once.  I'm not sure what trouble you are
>having.  If you are creating peices of the design as separate synthesis
>runs, those peices need to be instantiated as black boxes in a higher
>level design.  The top level will give each piece a different hierarchical
>name.  There can only be one top level netlist going into the xilinx
>tools.  Same with a simulator.

I think he is trying to synthesize two (or more) modules separately
and then simulate them in gate level. I can see why he is having the
problem. Synplify generates gate level primitives which are
instantiated in the generated module. The names of the generated
primitives don't have any hierarchy attached to them so when multiple
sub-blocks are synthesized, it is possible that all the generated
netlists will have similarly named primitives. I have no idea how one
would combine those gate-level outputs from synplify either. I guess
one can find all the modules, except the one which matches the file
name, and append the filename to their names. This way namespace
collision can be avoided. But that wouldn't be easy. I think the
script which would do it needs to understand some verilog syntax.

Muzaffer

FPGA DSP Consulting
http://www.dspia.com

Article: 32777
Subject: Simulation problems with BlockRAM's INIT values !
From: j.oblak@iskratel.si (Jure Oblak)
Date: 8 Jul 2001 23:27:46 -0700
Links: << >>  << T >>  << A >>
Hi,

I have a design that uses several BlockRAMs. These blockRAMs
(RAMB4_S16) should have a deafult value written in them. I am using
the following code to define the INIT values of blockRAMs

...
attribute INIT_00 : string;
attribute INIT_01 : string;
...
attribute INIT_00 of U1: label is
"0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF";
attribute INIT_01 of U1: label is
"0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF";
....

When I simulate I can write and read from blockRAMs normally but when
I just read I do not get a default value. Instead I get a zero. I am
using WebPACK 3.3 and ModelSIM 5.3 XE. The chip is Spartan2. Please
help!
Thank you in advance for your trouble you have taken.

Best regards

Jure Oblak

Article: 32778
Subject: Re: Simulation problems with BlockRAM's INIT values !
From: allan_herriman.hates.spam@agilent.com (Allan Herriman)
Date: Mon, 09 Jul 2001 06:51:00 GMT
Links: << >>  << T >>  << A >>
On 8 Jul 2001 23:27:46 -0700, j.oblak@iskratel.si (Jure Oblak) wrote:

>Hi,
>
>I have a design that uses several BlockRAMs. These blockRAMs
>(RAMB4_S16) should have a deafult value written in them. I am using
>the following code to define the INIT values of blockRAMs
>
>...
>attribute INIT_00 : string;
>attribute INIT_01 : string;
>...
>attribute INIT_00 of U1: label is
>"0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF";
>attribute INIT_01 of U1: label is
>"0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF";
>....
>
>When I simulate I can write and read from blockRAMs normally but when
>I just read I do not get a default value. Instead I get a zero. I am
>using WebPACK 3.3 and ModelSIM 5.3 XE. The chip is Spartan2. Please
>help!
>Thank you in advance for your trouble you have taken.

With block rams (and many other Xilinx primitives), the block rams
require the INIT generic to be set for simulation, and the attributes
to be set for synthesis.  (Don't ask me why, I don't write tools.)

I found the best way to cope with this was to write a wrapper around
the block ram which took the init value(s) as a generic, and then
passed these to the block ram as generics (with those horrid translate
on/off pragmas to ensure that the synthesiser doesn't see them), and
also created the attributes.  This way, the behaviour in simulation
matches the behaviour in the downloaded FPGA.
I wrote a function to convert the bit vector (of the generic) to a
string (for the attributes).

In an ideal world, you'd be able to get such a wrapper from the Xilinx
web site.   Xilinx Answer 2022 comes closest, but it's still a long
way from the mark.  (It only works in synthesis, not in simulation.)

Regards,
Allan.

Article: 32779
Subject: Re: Need some help using Synplify ... and also considering Xilinx
From: Rick Filipkiewicz <rick@algor.co.uk>
Date: Mon, 09 Jul 2001 08:08:22 +0100
Links: << >>  << T >>  << A >>


Muzaffer Kal wrote:

> On Mon, 09 Jul 2001 00:47:41 GMT, Ray Andraka <ray@andraka.com> wrote:
> >Synplicity is not a simulator, so I am not sure what you mean by
> >simulating two module netlists at once.  I'm not sure what trouble you are
> >having.  If you are creating peices of the design as separate synthesis
> >runs, those peices need to be instantiated as black boxes in a higher
> >level design.  The top level will give each piece a different hierarchical
> >name.  There can only be one top level netlist going into the xilinx
> >tools.  Same with a simulator.
>
> I think he is trying to synthesize two (or more) modules separately
> and then simulate them in gate level. I can see why he is having the
> problem. Synplify generates gate level primitives which are
> instantiated in the generated module. The names of the generated
> primitives don't have any hierarchy attached to them so when multiple
> sub-blocks are synthesized, it is possible that all the generated
> netlists will have similarly named primitives. I have no idea how one
> would combine those gate-level outputs from synplify either. I guess
> one can find all the modules, except the one which matches the file
> name, and append the filename to their names. This way namespace
> collision can be avoided. But that wouldn't be easy. I think the
> script which would do it needs to understand some verilog syntax.
>
> Muzaffer
>
> FPGA DSP Consulting
> http://www.dspia.com

There is a trick to simulating multiple independently synth'ed modules.
Basically what I do is to compile the post-synth Verilog netlists into separate
libs. In the top one, just before compilation, I hack in some `uselib
directives just before the instantiations of the lower level modules. This
works for Verilog+ModelSim, I don't know about VHDL+ANOtherSim.

Then I invoke the simulator with a lot of -L flags pointing to the compiled
post-synth netlists.

This has an advantage that when trying to track down a synth bug I can
mix&match RTL/post-synth to speed up simulation and make it easier to trace
signal names.



Article: 32780
Subject: Re: Max+2 and multi-cycle timing analysis WAS: Altera ACEX
From: Rick Collins <spamgoeshere4@yahoo.com>
Date: Mon, 09 Jul 2001 03:45:58 -0400
Links: << >>  << T >>  << A >>
Thanks Bob, for the advice. But we already thought of these suggestions.
My design takes about 30 minutes to run P&R. The timing analyzer takes
about an hour. So I find that to be very painful. 

It is also not easy to use the "ignore paths" option. We refer to this
as "cutting" the slow paths. The problem is that to identify the failing
paths, we have to use the timing analyzer again. Even worse, we have to
reenter the "cuts"; once for the P&R control and again for the timing
analyzer (TA). They use two different sections in the ACF file for this.
The TA needs the cuts in a different format which we have been using the
GUI to enter. Any time we change the design, we have to redo the "cuts"
in the changed sections. 

Finally, it did occur to us to add pipeline registers so that in effect,
the entire design becomes single clock cycle. This would not use any
additional LCs (at least in theory). But it would be significant work
and can involve a great deal of rework since much of the slow
combinatorial logic was coded in a way that we let the synthesizer deal
with the optimizations. 

Our methode seems to be the best compromize of time and resources. I am
just very surprized that the MaxPlus II software is so crude compared to
the Xilinx software I am used to. I have always heard that the Altera
software is so much better than the rest. 



bob elkind wrote:
> 
> some possible solutions/workarounds:
> 
> 1.  run timing analyser at 80/N MHz, to verify the multi-cycle paths;
> and then run timing analyser at 80 MHz for the "normal" logic paths
> (ignoring the spurious error reports for the multi-cycle paths).
> 
> 2.  insert gratuitous pipeline registers in the multi-cycle paths, to make
> the timing analyser happy.  If done with due clevernous, this may not
> even affect logic cell utilisation at all (in Altera Flex devices).
> 
> 3.  use the "ignore paths" facilities to guide the timing analyser.
> 
> You may need to declare the "result" registers of the multi-cycle paths
> as "LCELL"s at the top level of hierarchy, to ensure that their
> post-synthesis/post routing logical net names don't change from run
> to run.
> 
> As far as I know, this is a problem common to most/all timing analysers,
> with the design style you've chosen, and is not particularly peculiar to
> MAX+II.  If I'm off base on this, please correct me!
> 
> It is my understanding that Quartus II will eventually supercede the
> MAX+II tool (with perhaps excepting the 7Kx series of CPLDs),
> over time.  Don't delete MAX+II for at least 6 months after you *think*
> you're happy with Quartus II, as there will likely be weaknesses and
> holes in the "coverage" of any given product family as each family is
> first migrated from MAX+II to Quartus II.  Also, be prepared to max
> out your PCs' memory (SDRAM) capacity, as Quartus II (like most
> new generations of design tools) require more memory and more
> compute power to deliver the same (or more) polish and sophistication
> as the previous design tool generation.
> 
> Of course, I'm assuming that you haven't already tried these
> solutions and run into brick walls already, in which case I
> apologise for re-stating the obvioius...
> 
> -- Bob Elkind, the e-team  fpga/design consulting
> 
> Rick Collins wrote:
> 
> <quote deleted/skipped>
> 
> > We are working with the 10K parts on an existing board. We are
> > trying to do a design with an 80 MHz clock where a portion of the
> > circuit uses multiple clock cycles to process signals through
> > combinatorial logic. It would appear that the MaxPlus II tools so not
> > well support this type of design timing.
> >
> > The tool problems we have found are numerous. It is a bit like being in
> > a maze and finding every path blocked. Our final approach is to simply
> > constrain the entire design to 80 MHz, and manually examine all of the
> > failure reports. The failures on single clock paths are fixed. The
> > failures on multi-cycle paths are ignored. This is not fun as the
> > failing paths change on each iteration of place and route. We call this
> > the "whack-a-mole" approach. As you fix paths, other paths then fail.
> > Once you have a working design, any change makes more moles pop up.
> >
> > One pleasant note is that the next release of the Quartus tool is
> > supposed to support the 10K series. Quartus II has much better
> > multi-cycle support. I don't know if they intend to support the 1K ACEX
> > parts with Quartus II.
> >
> > --
> >
> > Rick "rickman" Collins
> >
> > rick.collins@XYarius.com
> > Ignore the reply address. To email me use the above address with the XY
> > removed.
> >
> > Arius - A Signal Processing Solutions Company
> > Specializing in DSP and FPGA design      URL http://www.arius.com
> > 4 King Ave                               301-682-7772 Voice
> > Frederick, MD 21701-3110                 301-682-7666 FAX


-- 

Rick "rickman" Collins

rick.collins@XYarius.com
Ignore the reply address. To email me use the above address with the XY
removed.

Arius - A Signal Processing Solutions Company
Specializing in DSP and FPGA design      URL http://www.arius.com
4 King Ave                               301-682-7772 Voice
Frederick, MD 21701-3110                 301-682-7666 FAX

Article: 32781
Subject: Clock buffers
From: "Noddy" <g9731642@campus.ru.ac.za>
Date: Mon, 9 Jul 2001 10:15:09 +0200
Links: << >>  << T >>  << A >>
Hi,

I'm using a Spartan 2 XC2S200 for the first time. Running at 32 Mhz, can
anyone suggest what clock buffers would be appropriate to use?

Adrian




Article: 32782
Subject: Re: Max+2 and multi-cycle timing analysis WAS: Altera ACEX
From: bob elkind <eteam@aracnet.com>
Date: Mon, 09 Jul 2001 01:34:18 -0700
Links: << >>  << T >>  << A >>
Rick,

1.  30 minutes for place and route is a *long* time for MAX+2.
That would (to me) imply a 1K100 or larger device, about 75% full.
What speed CPU are you running, how much memory, etc. ?  Are
you overdue for  a motherboard upgrade?

2.  Since the .ACF file is text format, it is relatively simple to add
change or delete "directives".  Alternative: maintain two copies of
the .ACF file, with and without "ignore" directives.  Don't just ignore
the "failing" paths... ignore *all* the multi-cycle paths.  This gets
you out of the re-entering of path names repetitive exercise.

2a.  Can you tweak your design structure ever so slightly so as to
avoid the name changes that compel you to re-enter path names?

3.  Presumably, the optimisation performed by the synthesiser
should be no greater or less with pipeline registers inserted in the
multi-cycle paths.  Same optimisations should apply.

As a note:  on an Acex1K-1 (fastest speed grade), a 32-bit ADD
plus 2 or more combinatorial logic levels can fit gracefully into a
12 nS path (roughly equivalent to your 85MHz clock cycle time).
If re-visiting your "legacy" combinatorial logic *once* will get you
out of the multi-cycle hacking that is an ongoing millstone, maybe
the logic redesign is a worthwhile venture...  Wouldn't it be nice
to get off this treadmill you (and your successors) are on ?

4.  I wouldn't necessarily characterise MAX+II as crude.  For many
designs, it is a turnkey solution that requires little or no tweaking to
obtain suitable results on the first go.  If you want to characterise this
behaviour as "unsophisticated", you're entitled to do so.  I'm fond of
such "unsophistication"... in fact, I actively pursue design structures
and styles that can be compiled and tested "with a single click".
Quartus and Foundation have more sophistication (read: more tweaks),
but I think that not needing such tweaks is the "sophistication" that
gets designs into production quicker, and saves clients money.
<... [your mileage will vary] disclaimer inserted here ...>.

By the way, Quartus II has 3 different files to provide the aggregate
functionality of the MAX+II .ACF file, and all three are *binary*,
not ASCII text.  There are workarounds, but I liked the idea of
being able to browse *all* the options that might affect a design,
from one file (not to mention seeing a text "diff" of two versions of
the .ACF file).

Interesting subject, Rick...  I'm sure this will be a recurring
discussion topic, in one form or another, within our online
community...

Good luck,

Bob Elkind, the e-team fpga/design consulting

Rick Collins wrote:

> Thanks Bob, for the advice. But we already thought of these suggestions.
> My design takes about 30 minutes to run P&R. The timing analyzer takes
> about an hour. So I find that to be very painful.
>
> It is also not easy to use the "ignore paths" option. We refer to this
> as "cutting" the slow paths. The problem is that to identify the failing
> paths, we have to use the timing analyzer again. Even worse, we have to
> reenter the "cuts"; once for the P&R control and again for the timing
> analyzer (TA). They use two different sections in the ACF file for this.
> The TA needs the cuts in a different format which we have been using the
> GUI to enter. Any time we change the design, we have to redo the "cuts"
> in the changed sections.
>
> Finally, it did occur to us to add pipeline registers so that in effect,
> the entire design becomes single clock cycle. This would not use any
> additional LCs (at least in theory). But it would be significant work
> and can involve a great deal of rework since much of the slow
> combinatorial logic was coded in a way that we let the synthesizer deal
> with the optimizations.
>
> Our methode seems to be the best compromize of time and resources. I am
> just very surprized that the MaxPlus II software is so crude compared to
> the Xilinx software I am used to. I have always heard that the Altera
> software is so much better than the rest.
>
> bob elkind wrote:
> >
> > some possible solutions/workarounds:
> >
> > 1.  run timing analyser at 80/N MHz, to verify the multi-cycle paths;
> > and then run timing analyser at 80 MHz for the "normal" logic paths
> > (ignoring the spurious error reports for the multi-cycle paths).
> >
> > 2.  insert gratuitous pipeline registers in the multi-cycle paths, to make
> > the timing analyser happy.  If done with due clevernous, this may not
> > even affect logic cell utilisation at all (in Altera Flex devices).
> >
> > 3.  use the "ignore paths" facilities to guide the timing analyser.
> >
> > You may need to declare the "result" registers of the multi-cycle paths
> > as "LCELL"s at the top level of hierarchy, to ensure that their
> > post-synthesis/post routing logical net names don't change from run
> > to run.
> >
> > As far as I know, this is a problem common to most/all timing analysers,
> > with the design style you've chosen, and is not particularly peculiar to
> > MAX+II.  If I'm off base on this, please correct me!
> >
> > It is my understanding that Quartus II will eventually supercede the
> > MAX+II tool (with perhaps excepting the 7Kx series of CPLDs),
> > over time.  Don't delete MAX+II for at least 6 months after you *think*
> > you're happy with Quartus II, as there will likely be weaknesses and
> > holes in the "coverage" of any given product family as each family is
> > first migrated from MAX+II to Quartus II.  Also, be prepared to max
> > out your PCs' memory (SDRAM) capacity, as Quartus II (like most
> > new generations of design tools) require more memory and more
> > compute power to deliver the same (or more) polish and sophistication
> > as the previous design tool generation.
> >
> > Of course, I'm assuming that you haven't already tried these
> > solutions and run into brick walls already, in which case I
> > apologise for re-stating the obvioius...
> >
> > -- Bob Elkind, the e-team  fpga/design consulting
>



Article: 32783
Subject: Online threshold limit counter
From: "Noddy" <g9731642@campus.ru.ac.za>
Date: Mon, 9 Jul 2001 12:27:39 +0200
Links: << >>  << T >>  << A >>
Hi all,

Can anyone think of a way (without using a whole lot of XOR gates) to create
a counter which has a threshold limit which can be updated via a port. Right
now, I am just using a standard counter, then using an input bus and the
output bus of the counter, XOR them all together and use result to reset the
counter. Is there a more efficient way?

Adrian




Article: 32784
Subject: Re: WTB:50 Mhz 24 CHANNEL LOGIC ANALYZER only $199
From: "Ulf Samuelsson" <ulf@atmel.dot.com>
Date: Mon, 9 Jul 2001 12:36:18 +0200
Links: << >>  << T >>  << A >>
you could do this inside an FPGA!


--
Best regards,
ulf at atmel dot com
The contents of this message is intended to be my private opinion and
may or may not be shared by my employer Atmel Sweden

"Ivan Vernot" <ivernot@ozemail.com.au> skrev i meddelandet
news:Ezj17.49677$Rr4.38763@ozemail.com.au...
>
> Hello FPGA Gurus,
> I've been trolling the Google archives for this news group looking for a
> Logic Analyzer that I may built as a kit (or buy cheaply)
>
> I came across reference in Oct 1996 for a company - 'ProBoard Circuits'
> which sell a cheap logic analyzer.
> Does anyone have any experience with this Company and have any further
> contact info?
> Can anyone point me in the right direction in being able to find a low
cost
> login analyzer for, relatively' low speed work.
>
> I am looking for something pretty basic - around 8 channels (min) -
perhaps
> 20 MHz max freq.
> Any ideas?
>
> TIA
> Ivan
>
>
>
>



Article: 32785
Subject: Re: SpartanII: non clock pad drives clock net ?
From: "Andrew Barnes" <andrew.barnes@linn.co.uk>
Date: Mon, 9 Jul 2001 05:37:30 -0700
Links: << >>  << T >>  << A >>
Hi all,

A similar problem has befallem me also. Using an XCS40XL, I find that I can get rid of the Multiple Drivers error message by deselecting the Create I/O Pads from Ports option, re-running Synthesis and Map, deleting the <design>.NGO file, re-selecting the Create I/O Pads, and re-running all.

However, when driving a clock signal from a GPIO pin, I get an OLDMAP:56 error stating that I can not lock (using the LOC constraint in the UCF) a clock signal, which is triggering a couple of simple processes, to site type CLKIOB. 

Any suggestions for how to proceed? Thankyou kindly for your assistance.

Article: 32786
Subject: Metastability constants for Altera FPGAs?
From: mmhotm@hotmail.com (Martin Melzer)
Date: 9 Jul 2001 05:58:09 -0700
Links: << >>  << T >>  << A >>
Does anyone know the metastability characteristics for the newer
Altera FPGAs like 10KE, 1K...? I know AN42, but it it quiet old they
have only the metastability constants for 6k, 7k, 8k 9k and 10k.

Martin

Article: 32787
Subject: Vitrtex selectram
From: Thomas Reinemann <thomas.reinemann@masch-bau.uni-magdeburg.de>
Date: Mon, 09 Jul 2001 15:39:06 +0200
Links: << >>  << T >>  << A >>
Hello,

the Xilinx Virtex FPGAs have block selectram and LUT selectram, what is
the difference between them? I read the Xilinx doc for the Virtex
family, but did not find any explanation for LUT selectram.

Furthermore, where can find an example to use them with VHDL.

Bye Tom!

Article: 32788
Subject: Re: SpartanII: non clock pad drives clock net ?
From: Magnus Homann <d0asta@licia.dtek.chalmers.se>
Date: 09 Jul 2001 15:53:40 +0200
Links: << >>  << T >>  << A >>
"Andrew Barnes" <andrew.barnes@linn.co.uk> writes:

> Hi all,
> 
> A similar problem has befallem me also. Using an XCS40XL, I find that I can get rid of the Multiple Drivers error message by deselecting the Create I/O Pads from Ports option, re-running Synthesis and Map, deleting the <design>.NGO file, re-selecting the Create I/O Pads, and re-running all.
> 
> However, when driving a clock signal from a GPIO pin, I get an OLDMAP:56 error stating that I can not lock (using the LOC constraint in the UCF) a clock signal, which is triggering a couple of simple processes, to site type CLKIOB. 
> 
> Any suggestions for how to proceed? Thankyou kindly for your assistance.

What synthesizer are you using? The synth is mapping the signal to a
global buffer, but you seem to place it in a non-global site. Tell
your synth toll not to generate a global buffer.

For Synplify:

library IEEE, synplify; 
use IEEE.std_logic_1164.all; 
use synplify.attributes.all; 

entity my_design is 
port (o : out std_logic; 
i, clk_in : in std_logic); 
atttribute syn_noclockbuf of clk_in : signal is true; 
end entity; 


Homann
-- 
Magnus Homann, M.Sc. CS & E
d0asta@dtek.chalmers.se

Article: 32789
Subject: Re: Vitrtex selectram
From: Keith R. Williams <krw@attglobal.net>
Date: Mon, 9 Jul 2001 10:04:18 -0400
Links: << >>  << T >>  << A >>
In article <3B49B3FA.20FD0F82@masch-bau.uni-magdeburg.de>, 
thomas.reinemann@masch-bau.uni-magdeburg.de says...
> Hello,
> 
> the Xilinx Virtex FPGAs have block selectram and LUT selectram, what is
> the difference between them? I read the Xilinx doc for the Virtex
> family, but did not find any explanation for LUT selectram.

Block SelectRAM is dedicated memory with built-in "free" dual ports.  
LUT SelectRAM is distributed throughout the LUTS on the chip. Basically 
a LUT is 16 bits of memory.  Stack 'em and rack 'em as needed.

> Furthermore, where can find an example to use them with VHDL.

It depends on your tools. Synplicity will infer distributed RAM from 
VHDL (not sure about BlockRAM). Look at Xilinx' APP notes and 
databooks.  CoreGen will create all sorts of interesting things out of 
them too. 

----
  Keith

Article: 32790
Subject: FLEX EPF8452A
From: "Abhimanyu Rastogi" <abhi_rastogi@hotmail.com>
Date: Mon, 09 Jul 2001 14:22:53 GMT
Links: << >>  << T >>  << A >>
Hi all,

I would like to know how the Altera FLEX EPF8452A implements the registers
and how difficult it would be to add some additional registers to support a
high-band daughter board.


I have also attached the existing interface between the micro and the altera
if that might help u....

Abhimanyu Rastogi
2nd year student
University of Ottawa
Canada



>>>>>>> editorial deletion of a uuencoded file




Article: 32791
Subject: Virtexe Config problem
From: wamsi_mohan@yahoo.com (Wamsi Mohan)
Date: 9 Jul 2001 08:23:36 -0700
Links: << >>  << T >>  << A >>
Hello.
 The problem I am facing is that when I try to configure the XCV600E
using selectMAP, the Done does not go high. However, INIT does not go
low either to indicate any config error.
I follow the usual steps of driving prog low and then high, waiting for
Init to go high and then clock the data[7:0]. Bitgen is compiled with
cclk option (as opposed to jtag clk or userclk). The mode pins are set
to 110 (select MAP). I have tried to abort the config cycle and read
back the status word. I read back 0xDF which Xilinx claims is correct.

Any thoughts?
Thanks
-Wamsi

Article: 32792
Subject: Re: Online threshold limit counter
From: John_H <johnhandwork@mail.com>
Date: Mon, 09 Jul 2001 15:28:11 GMT
Links: << >>  << T >>  << A >>
You mean like counting from 0 to 78 and resetting the counter to zero after you
reach 78?

Rather than resetting the counter to 0, I design my counters to reset (preload)
to -78 and count up to 0.  An added benefit:  the LSB of the counter (the sign
bit) can be used to directly drive the counter reset.

Very programmable.
- John

Noddy wrote:

> Hi all,
>
> Can anyone think of a way (without using a whole lot of XOR gates) to create
> a counter which has a threshold limit which can be updated via a port. Right
> now, I am just using a standard counter, then using an input bus and the
> output bus of the counter, XOR them all together and use result to reset the
> counter. Is there a more efficient way?
>
> Adrian


Article: 32793
Subject: Re: Max+2 and multi-cycle timing analysis WAS: Altera ACEX
From: Rick Collins <spamgoeshere4@yahoo.com>
Date: Mon, 09 Jul 2001 11:29:12 -0400
Links: << >>  << T >>  << A >>
bob elkind wrote:
> 
> Rick,
> 
> 1.  30 minutes for place and route is a *long* time for MAX+2.
> That would (to me) imply a 1K100 or larger device, about 75% full.
> What speed CPU are you running, how much memory, etc. ?  Are
> you overdue for  a motherboard upgrade?

I am running at 733 MHz with 128 MB memory. We are upgrading the memory,
but this does not change the basic fact that the timing analysis takes
twice as long as the P&R. 

 
> 2.  Since the .ACF file is text format, it is relatively simple to add
> change or delete "directives".  Alternative: maintain two copies of
> the .ACF file, with and without "ignore" directives.  Don't just ignore
> the "failing" paths... ignore *all* the multi-cycle paths.  This gets
> you out of the re-entering of path names repetitive exercise.

Yes, but two copies of the file is not the issue. 

 
> 2a.  Can you tweak your design structure ever so slightly so as to
> avoid the name changes that compel you to re-enter path names?

It is not a source file issue. Between the synthesizer and MaxPlusII,
the signal names are changed (to protect the innocent?) Since I can't
predict the exact names, I have to reenter the cuts so that they are
expanded uniquely for each design iteration. The perferred method would
be to use wildcards for the cuts. Or better yet, use the same ACF
entries for both P&R and timing analysis... no, the best approach would
be to produce the timing results when you run P&R. What a concept!!!
 

> 3.  Presumably, the optimisation performed by the synthesiser
> should be no greater or less with pipeline registers inserted in the
> multi-cycle paths.  Same optimisations should apply.

The point is that our code is not structured for insertion of pipeline
registers. The code is functionally oriented and the logic that results
is very different and frankly, unknown, since we don't really care.
Inserting pipeline registers will require a great deal of work to find
the points in the logic path where the delays are roughly equal.
Otherwise we will never make timing. Not so easy. 


> As a note:  on an Acex1K-1 (fastest speed grade), a 32-bit ADD
> plus 2 or more combinatorial logic levels can fit gracefully into a
> 12 nS path (roughly equivalent to your 85MHz clock cycle time).
> If re-visiting your "legacy" combinatorial logic *once* will get you
> out of the multi-cycle hacking that is an ongoing millstone, maybe
> the logic redesign is a worthwhile venture...  Wouldn't it be nice
> to get off this treadmill you (and your successors) are on ?

We are not working in a 1K part. We are using a 10K100 with 80 to 85%
utilization in each of 3 different downloads. 


> 4.  I wouldn't necessarily characterise MAX+II as crude.  For many
> designs, it is a turnkey solution that requires little or no tweaking to
> obtain suitable results on the first go.  If you want to characterise this
> behaviour as "unsophisticated", you're entitled to do so.  I'm fond of
> such "unsophistication"... in fact, I actively pursue design structures
> and styles that can be compiled and tested "with a single click".
> Quartus and Foundation have more sophistication (read: more tweaks),
> but I think that not needing such tweaks is the "sophistication" that
> gets designs into production quicker, and saves clients money.
> <... [your mileage will vary] disclaimer inserted here ...>.

I am calling it "crude" because it is VERY difficult to produce an
optimized design, even if working from schematic or other means of
highly controlled input format. I do understand that Altera has always
tried to make their devices and software work with a single button push
as much as possible. But it is not good when they make it so
unnecessarily difficult to optimize the design. All I really need is a
detailed timing report on the failed paths when I run P&R. Xilinx has
that; Lucent has that. What happened to Altera???


> By the way, Quartus II has 3 different files to provide the aggregate
> functionality of the MAX+II .ACF file, and all three are *binary*,
> not ASCII text.  There are workarounds, but I liked the idea of
> being able to browse *all* the options that might affect a design,
> from one file (not to mention seeing a text "diff" of two versions of
> the .ACF file).

We are simultaneously implementing this same design in a 20K part using
Quartus II. I was aware that there are multiple constraint files for
Quartus II, but I did not know that they are binary. We version control
all of our input files and it is very useful to be able to see changes.
Binary files prevent this from working. 

But then I am told that our method with Quartus II uses TCL scripts to
regenerate our constraints files from scratch each time we run. So we
just source control the TCL scripts. 


> Interesting subject, Rick...  I'm sure this will be a recurring
> discussion topic, in one form or another, within our online
> community...
> 
> Good luck,
> 
> Bob Elkind, the e-team fpga/design consulting

Interesting is the right word, but I am not sure everyone understands
the meaning. The Chineese have a curse, "May you live in interesting
times". 



-- 

Rick "rickman" Collins

rick.collins@XYarius.com
Ignore the reply address. To email me use the above address with the XY
removed.

Arius - A Signal Processing Solutions Company
Specializing in DSP and FPGA design      URL http://www.arius.com
4 King Ave                               301-682-7772 Voice
Frederick, MD 21701-3110                 301-682-7666 FAX

Article: 32794
Subject: Re: Need some help using Synplify ... and also considering Xilinx Modular Flow
From: "Kevin Neilson" <kevin_neilson@yahoo.com>
Date: Mon, 09 Jul 2001 16:16:42 GMT
Links: << >>  << T >>  << A >>
Chris,
I also prefer to use Synplify to enter all my constraints rather than using
the UCF.  Since Synplify is timing-driven, it's best to have the constraints
entered pre-synthesis.  However, I too have had troubles when it comes to
the DLL.  Synplify doesn't always recognize or pass on the fact that the
actual clock frequency is different than the DLL input, even when you're
using the "syn_keep" directive.  In this case you might have to use the UCF
for constraints.

However, a colleague pointed out to me that you can use the wildcard in
specifying Synplify multicycle constraints.  You could constrain the whole
design for 48MHz, and use the wildcard to specify which modules are 4-cycle
paths.  That is, instead of specifying each multicycle flop in the SDC file,
like "top.module1.flop1", you can specify "top.module1.*" and Synplify will
expand that in the NCF file that it passes to the router.  I don't think
this is in the Synplify documentation anywhere, but it works.

I think you can P&R each module separately, and then use the associated
placement file and guide file (for routing) for each when putting them all
together, but man would that be a pain.  For a 48MHz design you ought to be
able to P&R with just the timing constraints.

-Kevin

"chris" <cjwang_1225@hotmail.com> wrote in message
news:24a13eb0.0107081424.33c5c0b1@posting.google.com...
> hi all.
> i have a design that has two clocks on it, one at 48 mhz and one at 12
> mhz (48 mhz divide by 4). the divide down is done with the DLL on the
> Virtex 300 part. currently my design passes our simulation testbench
> after synthesis and place and route module by module, but when the
> whole thing is integrated and then goes through the design flow, then
> timing issues prevent the design from working at the specified speed.
> one thing i unsuccessfully tried was to get synplicity to recognize
> the 12 mhz and 48 mhz parts and optimize accordingly. i specified the
> different clock signals in SCOPE, but i still get the same warnings in
> the log file that some nets don't make the 48 mhz timing window (even
> though the nets are in the 12 mhz section). if i had to declare all
> the false or multicycle paths, it would kill me because there are so
> many. i was wondering if anyone has success in getting synplicity to
> recognize the different clock domains and optimize according to those
> frequencies.
> another thing is that i have a receive clock (RxClk) at 12 mhz which
> is derived from the incoming signal, and that clock has a lot of skew
> with my internal 12 mhz clock which it needs to be in phase with. is
> there a way to limit this clock to clock skew?
> and finally, in synplify i cannot simulate two separate module
> netlists at the same time. there is overlap between the modules it
> creates (ie: LUT3_2 or something like that) and it causes Verilog-XL
> to choke. does anyone know how to get around this problem? i have
> heard about the modular design option in synplify and am considering
> it.
> lastly, is it possible to place and route a design module by module?
> since i can get the pieces working but not the whole, i would like to
> PAR the pieces and then glue them together to make the whole.
> thanks for all the previous help. sorry this message is so long.
> chris
>



Article: 32795
Subject: Re: Shift and Add Multiplier With Signed Numbers
From: John_H <johnhandwork@mail.com>
Date: Mon, 09 Jul 2001 16:29:12 GMT
Links: << >>  << T >>  << A >>
It's pretty obvious that a positive second multiplicand works fine whether
the first multiplicand is positive or negative.  It's the second negative
that's a problem.  For any x and positive y

x * -y = x * (16-y)   for a 4 bit input

x * -y = x * 16 - x * y

Since what you want is

- x * y

you could just subtract out x*16.  So a shift and add with a final
subtract would get you to your goal

       1110
       1101
-----------
 ...1111110
 ...0000000
 ...1111000
 ...1110000
-----------
 ...1100110
-..11100000  -16*(-2)
-----------
 ...0000110

It's not pretty but it's one way to get there.  You could probably do an
internet search and find a better way to implement the 4 quadrant
multiplier.

Enjoy.
- John


Article: 32796
Subject: Re: Clock buffers
From: Falk Brunner <Falk.Brunner@gmx.de>
Date: Mon, 09 Jul 2001 18:37:00 +0200
Links: << >>  << T >>  << A >>
Noddy schrieb:
> 
> Hi,
> 
> I'm using a Spartan 2 XC2S200 for the first time. Running at 32 Mhz, can
> anyone suggest what clock buffers would be appropriate to use?

In general, one should use the global clock buffers (there are 4 of
them), regardless of your frequncy. Even at 1 kHz, the clock skew in
non-clock nets can (AND WILL!!) become too high and the design will
fail.

If you run out of clock nets, use longlines, wich have low skew. To do
this use the following command in your *.ucf file

NET my_net_name uselowskewlines;

-- 
MFG
Falk



Article: 32797
Subject: Re: Need some help using Synplify ... and also considering Xilinx
From: "Jason T. Wright" <Jason.T.Wright@Boeing.com>
Date: Mon, 9 Jul 2001 17:24:06 GMT
Links: << >>  << T >>  << A >>
It looks like you are doing some USB 1.x stuff.  I used Synopsys (&
later Exemplar) tools, essentially ignoring timing in synthesis and
constraining it all in the ucf.  Also, only a small portion of the
design I had was 48-MHz critical; you might try constraining it to 12
MHz, and just selecting the signals/paths that are 48-MHz critical and
applying those constraints in the ucf.

Jason

chris wrote:
> 
> hi all.
> i have a design that has two clocks on it, one at 48 mhz and one at 12
> mhz (48 mhz divide by 4). the divide down is done with the DLL on the
> Virtex 300 part. currently my design passes our simulation testbench
> after synthesis and place and route module by module, but when the
> whole thing is integrated and then goes through the design flow, then
> timing issues prevent the design from working at the specified speed.
> one thing i unsuccessfully tried was to get synplicity to recognize
> the 12 mhz and 48 mhz parts and optimize accordingly. i specified the
> different clock signals in SCOPE, but i still get the same warnings in
> the log file that some nets don't make the 48 mhz timing window (even
> though the nets are in the 12 mhz section). if i had to declare all
> the false or multicycle paths, it would kill me because there are so
> many. i was wondering if anyone has success in getting synplicity to
> recognize the different clock domains and optimize according to those
> frequencies.
> another thing is that i have a receive clock (RxClk) at 12 mhz which
> is derived from the incoming signal, and that clock has a lot of skew
> with my internal 12 mhz clock which it needs to be in phase with. is
> there a way to limit this clock to clock skew?
> and finally, in synplify i cannot simulate two separate module
> netlists at the same time. there is overlap between the modules it
> creates (ie: LUT3_2 or something like that) and it causes Verilog-XL
> to choke. does anyone know how to get around this problem? i have
> heard about the modular design option in synplify and am considering
> it.
> lastly, is it possible to place and route a design module by module?
> since i can get the pieces working but not the whole, i would like to
> PAR the pieces and then glue them together to make the whole.
> thanks for all the previous help. sorry this message is so long.
> chris

-- 
Jason T. Wright

The opinions I express are my own ...
    unless otherwise indicated!

Article: 32798
Subject: Re: Max+2 and multi-cycle timing analysis WAS: Altera ACEX
From: Mike Treseler <mike.treseler@flukenetworks.com>
Date: Mon, 09 Jul 2001 12:02:30 -0700
Links: << >>  << T >>  << A >>
bob elkind wrote:

> By the way, Quartus II has 3 different files to provide the aggregate
> functionality of the MAX+II .ACF file, and all three are *binary*,
> not ASCII text.  

This is not true.
The quartus settings files are .CSF, .PSF and .ESF.
They are all ASCII text.
The only binary files are for the internal database.

      -Mike Treseler

Article: 32799
Subject: Re: XC9500 drive capability
From: Mark Ng <mark.ng@xilinx.com>
Date: Mon, 09 Jul 2001 12:17:31 -0700
Links: << >>  << T >>  << A >>
All 9500 data sheets list which Function Block and Macrocell a particular I/O
pin resides in.  Given that, you can judge which pins are adjacent on the die.

If your IO pins fall in between two function blocks, you can usually tell if
they are adjacent by looking at the pin numbers.  They are adjacent as the pin
numbers increase...

I hope that helps..

Mark

Rick Filipkiewicz wrote:

> Peter Alfke wrote:
>
> > Yes, it works. All these output structures are almost the same.
> > The issue is to what extent the current divides equally between
> > the two drivers. And if they have the same basic characteristic,
> > and are adjacent on the die, they track very well.
> >
> > Peter Alfke, Xilinx Applications
> >
> > Vitali wrote:
> >
> > > Hello,
> > >
> > > can I double current sink capability by tying two output pins?
> > > I know it runs on FPGAs (on "senior" XC4000s). How about CPLDs?
> > >
> > > Thanks
> > >
> > > Vitali.
>
> How can you tell which IOs are next to each other on the die for an
> XC95K part ? For Virtex devices you can get this info from a .par report
> file.




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