Xilinx 8.2 : Multippass P&R

Hi,

I was hoping that someone could point me at a useful document or other
link.
Our FPGA build flow is currently scripted for a single iteration  P&R.
Unfortunately, we are now starting to get some hold violations.
If I run a multipass P&R, approximately 50% of the iterations will
yeild successful timing (Timing Score = 0).

Ideally, what I want is a method of saying : Iterate until timing met,
with a maximum of n

What I get is n P&R'ed design files. Is there a simple method of
identifying which of these designs met timing (via a CSH script).

FYI, the (CSH) command line I am using is:

    par -intstyle xflow -n $Num_Iterations -w -xe c -ol high -ub
des.ncd des.dir des.pcf

Any suggestions ?

Thanks in advance,

Steven

I think you can monitor the des.par file created next to the des.dir
directory.
It gives you something like:
Constraints file: ../map/rmpl_4.pcf.

Level/      Design      Timing      Number      Run         NCD
Cost [ncd]  Score       Score       Unrouted    Time        Status
----------  ------      --------    --------    -----
------------
H_S_2   *   215636      262882      0           31:23
Complete
H_S_3   *   265943      228477      0           40:51
Complete
...
* : Design saved.

It seems to be updated after each run. I think I was using ISE 7.1 at
the time.
Once you find "design score" or "timing score" (see xilinx AN3749)
equal to zero
you can kill the par process and use the working one.

I also tried to run multipar with high placer effort (-pl high) but
lower routing effort (-rl std)
to find the best place result, then reroute (par -k) this with higher
routing effort (-rl high).

I used this script to parse the .par file (hope it still works):

# This script returns the path to the "best" result from mppr. Lower
Design score is better.
# Only look at files which have a "*" (design saved) and NCD status
complete.
# $1 is the mppr.par file to parse, $2 is the ranking to use, default
is 1 (i.e. best)
# $1 also hints about the directory due to xilinx's naming convension.
file=$1
result_dir=$(echo $file | sed -e "s/\.par/\.dir/")

if [ "$2" = "" ]; then
    rank=1
else
    rank=$2
fi

best_result=$(cat $file | grep "\\*" | grep "Complete" | sort -n -k3 |
sed -ne "${rank}p" | sed -e "s/[ \t].*$//")

echo "${result_dir}/${best_result}.ncd"

#last line

On May 24, 8:11 am, pontus.stenst...@gmail.com wrote:
> I think you can monitor the des.par file created next to the des.dir
> directory.
> It gives you something like:
> Constraints file: ../map/rmpl_4.pcf.
>
> Level/      Design      Timing      Number      Run         NCD
> Cost [ncd]  Score       Score       Unrouted    Time        Status
> ----------  ------      --------    --------    -----
> ------------
> H_S_2   *   215636      262882      0           31:23
> Complete
> H_S_3   *   265943      228477      0           40:51
> Complete
> ...
> * : Design saved.
>
> It seems to be updated after each run. I think I was using ISE 7.1 at
> the time.
> Once you find "design score" or "timing score" (see xilinx AN3749)
> equal to zero
> you can kill the par process and use the working one.
>
> I also tried to run multipar with high placer effort (-pl high) but
> lower routing effort (-rl std)
> to find the best place result, then reroute (par -k) this with higher
> routing effort (-rl high).
>
> I used this script to parse the .par file (hope it still works):
>
> # This script returns the path to the "best" result from mppr. Lower
> Design score is better.
> # Only look at files which have a "*" (design saved) and NCD status
> complete.
> # $1 is the mppr.par file to parse, $2 is the ranking to use, default
> is 1 (i.e. best)
> # $1 also hints about the directory due to xilinx's naming convension.
> file=$1
> result_dir=$(echo $file | sed -e "s/\.par/\.dir/")
>
> if [ "$2" = "" ]; then
>     rank=1
> else
>     rank=$2
> fi
>
> best_result=$(cat $file | grep "\\*" | grep "Complete" | sort -n -k3 |
> sed -ne "${rank}p" | sed -e "s/[ \t].*$//")
>
> echo "${result_dir}/${best_result}.ncd"
>
> #last line


I'm not sure if they fixed the bug in 8.2, but in older versions
of ISE, the results for multipass place & route did not necessarily
correspond to the single-pass results for the same cost table entry.

In any case if you're using a script to run place&route, why not let
the script handle multipass using the -t command line argument to
set the cost table entry on each pass.  Also many times you get better
results by using the timing option for map.  In this case you'll
find that multipass place&route doesn't help much because it starts
from a more completely mapped design.  A script could re-run map
and place&route with a new cost table entry each pass, then look
at the report file as mentioned to decide when to stop.

HTH,
Gabor

On 24 May, 15:44, Gabor <g...@alacron.com> wrote:
> I'm not sure if they fixed the bug in 8.2, but in older versions
> of ISE, the results for multipass place & route did not necessarily
> correspond to the single-pass results for the same cost table entry.
>
> In any case if you're using a script to run place&route, why not let
> the script handle multipass using the -t command line argument to
> set the cost table entry on each pass.  Also many times you get better
> results by using the timing option for map.  In this case you'll
> find that multipass place&route doesn't help much because it starts
> from a more completely mapped design.  A script could re-run map
> and place&route with a new cost table entry each pass, then look
> at the report file as mentioned to decide when to stop.
>
> HTH,
> Gabor- Hide quoted text -
>
> - Show quoted text -

Hi Gabor,

I'm afraid that your post goes beyond the level of my knowledge :-(

Can you please clarify what a "Cost Table Entry" is, and how do you
select one.

Thanks,

Steven

On 24 May, 14:11, pontus.stenst...@gmail.com wrote:
> I think you can monitor the des.par file created next to the des.dir
> directory.
> It gives you something like:
> Constraints file: ../map/rmpl_4.pcf.
>
> Level/      Design      Timing      Number      Run         NCD
> Cost [ncd]  Score       Score       Unrouted    Time        Status
> ----------  ------      --------    --------    -----
> ------------
> H_S_2   *   215636      262882      0           31:23
> Complete
> H_S_3   *   265943      228477      0           40:51
> Complete
> ...
> * : Design saved.
>
> It seems to be updated after each run. I think I was using ISE 7.1 at
> the time.
> Once you find "design score" or "timing score" (see xilinx AN3749)
> equal to zero
> you can kill the par process and use the working one.
>
> I also tried to run multipar with high placer effort (-pl high) but
> lower routing effort (-rl std)
> to find the best place result, then reroute (par -k) this with higher
> routing effort (-rl high).
>
> I used this script to parse the .par file (hope it still works):
>
> # This script returns the path to the "best" result from mppr. Lower
> Design score is better.
> # Only look at files which have a "*" (design saved) and NCD status
> complete.
> # $1 is the mppr.par file to parse, $2 is the ranking to use, default
> is 1 (i.e. best)
> # $1 also hints about the directory due to xilinx's naming convension.
> file=$1
> result_dir=$(echo $file | sed -e "s/\.par/\.dir/")
>
> if [ "$2" = "" ]; then
>     rank=1
> else
>     rank=$2
> fi
>
> best_result=$(cat $file | grep "\\*" | grep "Complete" | sort -n -k3 |
> sed -ne "${rank}p" | sed -e "s/[ \t].*$//")
>
> echo "${result_dir}/${best_result}.ncd"
>
> #last line

Thanks. This is just the information I was after.

Steven

On May 24, 10:26 am, moo...@yahoo.co.uk wrote:
> On 24 May, 15:44, Gabor <g...@alacron.com> wrote:
>
>
>
> > I'm not sure if they fixed the bug in 8.2, but in older versions
> > of ISE, the results for multipass place & route did not necessarily
> > correspond to the single-pass results for the same cost table entry.
>
> > In any case if you're using a script to run place&route, why not let
> > the script handle multipass using the -t command line argument to
> > set the cost table entry on each pass.  Also many times you get better
> > results by using the timing option for map.  In this case you'll
> > find that multipass place&route doesn't help much because it starts
> > from a more completely mapped design.  A script could re-run map
> > and place&route with a new cost table entry each pass, then look
> > at the report file as mentioned to decide when to stop.
>
> > HTH,
> > Gabor- Hide quoted text -
>
> > - Show quoted text -
>
> Hi Gabor,
>
> I'm afraid that your post goes beyond the level of my knowledge :-(
>
> Can you please clarify what a "Cost Table Entry" is, and how do you
> select one.
>
> Thanks,
>
> Steven


If you look in the Development System Reference Guide, it lists
all of the command line options for "par" (place&route).  The -t
option sets the starting "Placer Cost Table".  I'm not sure why
they call it that (maybe someone from NeoCad can give a hint?)
but it is essentially a seed for initial placement.  This is the
number that is incremented on each pass of multipass place and
route.  If you don't specify a number it defaults to 1.  So in
your case:

par -intstyle xflow -n $Num_Iterations -w -xe c -ol high -ub

is similar to

for $iteration = 1 to $Num_Iterations

par -intstyle xflow -t $iteration -w -xe c -ol high -ub

This runs one place and route pass per loop rather than letting
par.exe determine the number of loops.  Map, when timing mode
is enabled, also allows you to specify the starting placer
cost table.  This is a newer feature than the 6.1i that I
normally work with.  I know it's in 9.1i anyway.  If you
use the GUI, look at the properties for Map and make sure
you have advanced properties displayed.  The first item is
"Perform timing driven packing and placement".  If you check
this box the settings for effort level and starting placer
cost table will be enabled.  You'll need to look at the
Development System Reference Guide to see how to do this
from the command line, or you can run map from the GUI and
see the command in the log file.

HTH,
Gabor

On 2007-05-25, Brian Drummond <brian_drummond@btconnect.com> wrote:
> Consider a shell script which launches PARs one at a time ( for bonus
> points, n at a time on a multi-core machine!), each with a separate cost
> table entry (-t nn).

You might also be able to improve your results by varying your timing
constraints slightly instead of using a separate cost table. (I've recently 
played with a design which would meet timing with a cycle time constraint
of 4.8 ns, fail at 4.9 ns and succeed again at 5.0 ns. )

/Andreas

On 24 May 2007 04:35:28 -0700, moogyd@yahoo.co.uk wrote:

>Hi,
>
>I was hoping that someone could point me at a useful document or other
>link.
>Our FPGA build flow is currently scripted for a single iteration  P&R.
>Unfortunately, we are now starting to get some hold violations.
>If I run a multipass P&R, approximately 50% of the iterations will
>yeild successful timing (Timing Score = 0).
>
>Ideally, what I want is a method of saying : Iterate until timing met,
>with a maximum of n

MPPR may not be the best idea here; 
(a) because you have to "kill" it when done, and handle the resulting
file renamings yourself, and 
(b) because when a PAR aborts with the famous "portability errors", it
also kills MPPR instead of starting the next pass at PAR. So you find
out next morning, MPPR stopped about ten minutes after you left the
office. Unless PAR has become 100% reliable since 7.1...

Consider a shell script which launches PARs one at a time ( for bonus
points, n at a time on a multi-core machine!), each with a separate cost
table entry (-t nn).

The script will have to look at each .PAR file (once the  PAR has
completed) and search for "all constraints were met" or the appropriate
phase.

- Brian

On 2007-05-30, moogyd@yahoo.co.uk <moogyd@yahoo.co.uk> wrote:
> On 25 May, 14:19, Andreas Ehliar <ehl...@lysator.liu.se> wrote:
>> You might also be able to improve your results by varying your timing
>> constraints slightly instead of using a separate cost table. (I've recently
>> played with a design which would meet timing with a cycle time constraint
>> of 4.8 ns, fail at 4.9 ns and succeed again at 5.0 ns. )
>>
>
> This is certainly something I do with ASIC synthesis tools (synopsys).
> It was quite easy using the TCL command interface, which I don't think
> is available using ISE (please correct eme if I am wrong).

There actually is a TCL command interface available in the current
ISE version. (I think it was added in ISE 8.2.) Some documentation is
available in the $XILINX/doc/usenglish/books/docs/dev/dev.pdf file of
your ISE installation.  You can either use the TCL prompt in Project
Navigator or use xtclsh directly it seems.

Is your experience regarding timing constraints for ASIC
synthesis/backend tools the same as mine in regards to FPGA
synthesis/backend tools?


> One of the problems I am finding with the (admittedly free) Xilinx
> tools is poor command line and scripting capabilities. Real engineers
> don't use GUI's ;-)

I actually don't find the Xilinx command line tools that limiting if
you have a decent framework to use. If you are interested I have a Makefile
based flow for synthesizing an FPGA design available for download on my
homepage which could serve as inspiration. Look for the PPC405 based design
on http://www.da.isy.liu.se/~ehliar/stuff/ (No EDK is needed for this
design.)

/Andreas

On 25 May, 14:19, Andreas Ehliar <ehl...@lysator.liu.se> wrote:
> On 2007-05-25, Brian Drummond <brian_drumm...@btconnect.com> wrote:
>
> > Consider a shell script which launches PARs one at a time ( for bonus
> > points, n at a time on a multi-core machine!), each with a separate cost
> > table entry (-t nn).
>
> You might also be able to improve your results by varying your timing
> constraints slightly instead of using a separate cost table. (I've recently
> played with a design which would meet timing with a cycle time constraint
> of 4.8 ns, fail at 4.9 ns and succeed again at 5.0 ns. )
>
> /Andreas

This is certainly something I do with ASIC synthesis tools (synopsys).
It was quite easy using the TCL command interface, which I don't think
is available using ISE (please correct eme if I am wrong).

One of the problems I am finding with the (admittedly free) Xilinx
tools is poor command line and scripting capabilities. Real engineers
don't use GUI's ;-)