UPGRADE YOUR BROWSER

We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

cancel
Showing results for 
Search instead for 
Did you mean: 
10,561 Views
Registered: ‎12-07-2008

Multipass Place and Route

Jump to solution

Hi all,

I'm working on  a large desing  and I'm having some problems making it respect timing constraint.

So I tried MultiPass Place and Route with just 2 iterations

The first one ended with an error saying that was not possible to completely route all the design ... the second one instead routed the design respecting the constraint.

 

Attached you'll find the last part of the report it says that PAR failed ... but one of the iterations succeded!!!

How can I use it to generate my bitstream?!?!?

 

I tried to use the .ncd file produced as imput for a guided par ... but at the end it didn't respect the timing constraint!

How it is possible??

 

I'm using Xilinx ISE8.2sp3

 

....

Placement: Completed - No errors found.
Routing: Completed - No errors found.
Timing: Completed - No errors found.

Number of error messages: 0
Number of warning messages: 17
Number of info messages: 3

Writing design to file C:/Progetti/ICS8550-L50/G11464-002/ICS_8550/mppr_result.dir/H_H_2.ncd



PAR done!

Process "Place & Route" failed

0 Kudos
1 Solution

Accepted Solutions
Instructor
Instructor
12,409 Views
Registered: ‎08-14-2007

Re: Multipass Place and Route

Jump to solution

You could try turning off Timing Driven packing & placement, but usually that option

helps when trying to place and route large designs that are having trouble making

timing.

 

Other things to try:

 

If you still have the placement that "met timing" but also "failed" perhaps you can

open it in FPGA editor.  Often just using the placement for non-fabric resources

like block rams and multipliers/DSP units can help P&R to give you a usable

result.

 

Upgrade to a newer version of ISE.  You can have multiple versions on the

same system, so if there are issues with the newer tools you can easily go

back to 8.2.  Also if you use the latest version of the tools you may get

better response from Xiinx when you find bugs.

 

Look through the post P&R timing report for a pass that doesn't meet timing

and see if you can fix the timing problems by relaxing some constraints or

changing the design. You may also get help by playing with synthesis, translate

and map options like register balancing, register replication, shutting

off resource sharing, etc.

 

Regards,

Gabor

-- Gabor
0 Kudos
6 Replies
Instructor
Instructor
10,546 Views
Registered: ‎08-14-2007

Re: Multipass Place and Route

Jump to solution

As a workaround, you should be able to get the same results from a single-pass

place and route if you use the cost table entry from the multipass P&R that

gave your desired results.  For example if your starting cost table was 1

(default) and the second pass (using table entry 2) completed and

met timing, you could just change the starting cost table entry to 2 in

your P&R settings and run standard place & route instead.

 

Regards,

Gabor

-- Gabor
0 Kudos
Highlighted
10,543 Views
Registered: ‎12-07-2008

Re: Multipass Place and Route

Jump to solution

that's what I thought too... but I tried with a single pass place and route setting the cost table entry to 2 and ... it didn't work.

The routing was different from what I got with multipass, timing constraint were not met.

I'm pretty confused.

0 Kudos
Instructor
Instructor
10,540 Views
Registered: ‎08-14-2007

Re: Multipass Place and Route

Jump to solution

I thought that issue was fixed in 8.2, apparently not.  You can always do a "manual multipass P&R"

as a workaround, changing the starting cost table entry for each pass manually and running

the standard P&R.  When you ran the multipass P&R were you using "Timing driven packing and

placement" in your mapping options?  This option effectively causes multi-pass P&R to

do just re-entrant routing since the placement is done by the mapper and that is not

re-run in the loop.

-- Gabor
10,517 Views
Registered: ‎12-07-2008

Re: Multipass Place and Route

Jump to solution

Yes I did use "Timing driven packing and placement". So if I understand well if it is re-entrant ... the placement that MPRR calls 2 is not the one obtained with cost table entry to 2 but it is also dependent on the first placement.

 

So what can I do? Maybe deactivating Timing driven packing I can test if multipass is able to reach a working placement.

Or as you suggest run multiple PR by changing manually the starting cost table.

 

That's very annoying in any case ...

0 Kudos
Instructor
Instructor
12,410 Views
Registered: ‎08-14-2007

Re: Multipass Place and Route

Jump to solution

You could try turning off Timing Driven packing & placement, but usually that option

helps when trying to place and route large designs that are having trouble making

timing.

 

Other things to try:

 

If you still have the placement that "met timing" but also "failed" perhaps you can

open it in FPGA editor.  Often just using the placement for non-fabric resources

like block rams and multipliers/DSP units can help P&R to give you a usable

result.

 

Upgrade to a newer version of ISE.  You can have multiple versions on the

same system, so if there are issues with the newer tools you can easily go

back to 8.2.  Also if you use the latest version of the tools you may get

better response from Xiinx when you find bugs.

 

Look through the post P&R timing report for a pass that doesn't meet timing

and see if you can fix the timing problems by relaxing some constraints or

changing the design. You may also get help by playing with synthesis, translate

and map options like register balancing, register replication, shutting

off resource sharing, etc.

 

Regards,

Gabor

-- Gabor
0 Kudos
10,442 Views
Registered: ‎12-07-2008

Re: Multipass Place and Route

Jump to solution

Finally I turned off Timing Driven packing & placement and run Multi Pass Place & Route.

It met the timing constraint at the second iteration .. then I run a Normal Place & Route setting the Cost Table entry to 2, and it worked.

 

Anyway everytime I change also little particulars I have to face with this problems Timing Constraints, Guide Map and PAR helped a little bit in the past  ... but   it doesn't work always as expected.

Unfortunately I can't relax the constraint and I can't update to the newer ISE version.

 

Thanks

0 Kudos