[DFTC] Issue in scan chain specification

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maulin sheth

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Hello All,

I have done scan insertion using Synopsys DFT Compiler.
I have give specification like :
set_scan_specification -chain_count 32.

But preview_dft report shows the 33 chain_count. Why this occurs? Is there any specific reason for this?

Thanks & Regards,
Maulin.
 
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    shivad

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i think it should be "set_scan_configuration -chain_count 32"
 

Hello,
I have already mentioned in the thread that I have used set_scan_configuration -chain_count 32 but DFT compiler inserts 33 scan chains...I dont have any problem with 33 scan chain..But I want to know why this going to be happened?
 

Sorry dude.. for reiterating but your initial post said "set_scan_specification" so i thought would be a typo.

Coming to the issue a quick thought is that this is honored during only compression mode. Also i would if your not triggering auto scan connection some place which is overriding this setting.
 

Usually it is happended when other configuration options can't be done. Specify other ones (like mix_clocks) you use. And also specify preview_dft log. It will show which clocks used to scan every chain, it helps to debug.
 

Hello ed,
Its ok...Thanks for help...Yea I am also thing the same but I am not using scan compression mode..I am inserting using only scan..not scan compression.., But I have just enable the autofix option for clock using set_dft_configuration -fix_clock enable..other thn that, I have not use any autofix logic/command (e.g. set_autofix_configuration)...But Do you think so that this is the only reason or have you any other idea?

Hello kornukhin,
Yea, Its true that preview_dft log shows 33 scan chains...but I am not using the mix_clocks...and can I know which are the other configuration options which are not going to be done..

Anyone have a idea about preview_dft -script in Synopsys DFT Compiler?

Thanks..
 

I think the autofix is the culprit and is overriding your maxscan chain specification.
I would suggest to give a try without it and see, if it still cannot suffice the scan chain length then it will stop and give an Warning / Error that cannot meet scan requirements.

You can try preview once after disabling the autofix.
 

Hello,
Thanks..But whenver I will try to do scan without autofix, there are so many violations..which are solved by using autofix...is there any other solution to solve violation...pl Help the solution without doing manually...scripting is ok...
 

I would check what kind of violations are these. You may have missed defining some of the test signals.
See if you can perfrom some sort of dft_setup reporting after the autofix, it may export some of the signals that it is assuming some constants probably or gating a signal (rst / cgenable)
 

Hello,

It is solved. Thanks for helping me.
But the issue is different. The issue is in the design itself.

Thanks,
Maulin
 

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