How to solve a scan chain blocked problem in DFT compiler?

[S.Nikhil]

Hi,

I am currently utilizing Synopsys to do DFT for a large design. I have done scan insertion (30 Scan Chains) using DFT Compiler.

Currently at ATPG Stage (run drc), I notice that scan chain 20 is blocked after tracing through 392 cells out of total 1100 cells in the scan chain.

I do not have Tetramax GUI facility.

Can anyone guide me how to resolve this issue.

 

[lakshman.ar]

scan chain blocked

scan chain blocking will be present due to

1) uncontrollable clock
2) uncontrollable set/reset signals !!

uncontrollable signals will be present in ur design incase if ur control signals ( clock, set/rst) of the FF, comes from a combinational logic !!!

means to say tht wen u apply the scan vectors, the patterns ( gen by ur ATPG tool) cannot successfully traverse thru all the FF in the scan chain

This problem should hv been fixed at the DFT compiler level itself, evn b4 the generation of ATPG vectors !!!

The reason is tht, while fixing the DRC errors , the DFTC mite not have fixed it completely, its advisable to manually( by specifying the insertion of MUX or and or OR gates .... depends ) fix the DRC error !!!

are there multiple clock in ur design ??? ... if so, LOCK UP latches should also be inserted when there are multiple clock domains in the same scan chain !!

Please chk with the tool settings when u are fixing hte DRC errors, tht should solve the problem !!

WBR
Lakshman

 

[dft_guy]

Re: scan chain blocked

Hmmm, I didn't think that TetraMaX shipped without the graphical interface - I don't use TMAX every day, but you might go over to DFT Forum and ask, because I know that there are people who read it do use TMAX.

However, the first reply was correct - it's either a clock or a reset - you'll need to trace them back to their origins to find if they're controllable by primary input - normally TMAX can figure out what clocks/resets need to be controlled, but you may have to specify them if it can't.

John
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[Thinkie]

scan chain blocked

I am sure you can start the GUI interface...

Anyway.. find the cell and usually the problem will be obvious. Either a gating with something you have no control of , a bad reset .....

Try to have all scan chains connected directly from register to register with no logic (other than inverters) inbetween