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Visitor dawang
Visitor
263 Views
Registered: ‎12-19-2018

Using 18.1 netlists as reference in 18.3 Vivado, Vivado 18.3 gives up on the incremental flow, even though the logic diff is very small.

Hi, Vivado experts 

 

I have some minor design changes I would like to use the incremental flow to fast timing closure. 

My reference netlist1 was generated in 18.1. The timing was met in netlist1. I have a new netlist2, which was also generated in 18.1, timing was not met. I could use the 18.3 to read dcp file of the new netlist2 and run through incremental flow with reference set to netlist1, to make netlist2 timing meet. This indeed shows the adavntages of using increamental flow. 

 

1. Reuse Summary
----------------

+-------+----------------------+--------------------+--------------------+---------+
| Type | Matched % (of Total) | Reuse % (of Total) | Fixed % (of Total) | Total |
+-------+----------------------+--------------------+--------------------+---------+
| Cells | 99.76 | 99.77 | 0.13 | 586755 |
| Nets | 99.73 | 99.66 | 0.00 | 569873 |
| Pins | - | 99.69 | - | 2450580 |
| Ports | 100.00 | 100.00 | 100.00 | 670 |
+-------+----------------------+--------------------+--------------------+---------+
* Reused % can exceed matched % when unmatched cells take their placement directly from other cells that have been matched

 

However, I synthesize the same RTL with 18.3 from scratch, and generated netlist3. When I used netlist3 against netlist1 in the incremental flow of 18.3, Vivado says two netlists do not meet incremental threashold, so the tool gives up. 

I am very sure the design difference is very small. Not sure how this could happen. One thing I could guess is the transceivers IPs are updated from 18.1 to 18.3. 

 

Time (s): cpu = 00:00:54 ; elapsed = 00:01:51 . Memory (MB): peak = 10581.301 ; gain = 0.000 ; free physical = 25338 ; free virtual = 54469
WARNING: [Project 1-964] Cell Matching & Net Matching is less than the threshold needed to run Incremental flow. Switching to default Implementation flow

 

Any suggestions is very appreciated!

 

Thanks

David

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3 Replies
Moderator
Moderator
218 Views
Registered: ‎01-16-2013

Re: Using 18.1 netlists as reference in 18.3 Vivado, Vivado 18.3 gives up on the incremental flow, even though the logic diff is very small.

@dawang

 

After reading netlist 3 for top design and reading netlist 1 for incremental compilation, run the following command and check the reuse percentage:

report_incremental_reuse 

https://www.xilinx.com/support/documentation/sw_manuals/xilinx2018_3/ug904-vivado-implementation.pdf#page=102

example: 

open_checkpoint netlist3.dcp

read_checkpoint -incremental netlist1.dcp 

report_incremental_reuse 

 

--Syed

 

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Did you check our new quick reference timing closure guide (UG1292)?
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Visitor dawang
Visitor
206 Views
Registered: ‎12-19-2018

Re: Using 18.1 netlists as reference in 18.3 Vivado, Vivado 18.3 gives up on the incremental flow, even though the logic diff is very small.

Looks like no further info when Vivado decided backoff. Below are feedbacks from Vivado. 

 

report_incremental_reuse
INFO: [Vivado_Tcl 4-1062] Incremental flow is disabled. No incremental reuse Info to report.

 

Any other suggestions?

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Moderator
Moderator
193 Views
Registered: ‎01-16-2013

Re: Using 18.1 netlists as reference in 18.3 Vivado, Vivado 18.3 gives up on the incremental flow, even though the logic diff is very small.

@dawang

 

Can you share the files to debug the issue?

 

--Syed

---------------------------------------------------------------------------------------------
Kindly note- Please mark the Answer as "Accept as solution" if information provided is helpful.
Give Kudos to a post which you think is helpful and reply oriented.

Did you check our new quick reference timing closure guide (UG1292)?
---------------------------------------------------------------------------------------------
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