so lower dft coverage, why?

[HolySaint]

tetramax fastscan coverage

Here i use estimate_test_coverage commond to estimate the testcoverage

what a low testcoverage

RPT
================================================

----------------------------------------------------------
#patterns #faults #ATPG faults test process
stored detect/active red/au/abort coverage CPU time
--------- ------------- ------------ -------- --------
Begin deterministic ATPG: #uncollapsed_faults=1755508, abort_limit=10...
Warning: Chain test pattern failed contention checking (ID=542). (M430)
0 77035 1673479 1013/2772/1173863 8.77% 513.36
Warning: 1152726 faults aborted during contention prevention. (M139)

Pattern Summary Report
-----------------------------------------------
#internal patterns 0
-----------------------------------------------

Uncollapsed Stuck Fault Summary Report
-----------------------------------------------
fault class code #faults
------------------------------ ---- ---------
Detected DT 77035
Possibly detected PT 155113
Undetectable UD 142983
ATPG untestable AU 11499
Not detected ND 1518366
-----------------------------------------------
total faults 1904996
test coverage 8.77%
-----------------------------------------------
Information: The test coverage above may be inferior
than the real test coverage with customized
protocol and test simulation library.

==============================================

who can tell me which part may be wrong?
the design i load is produced by DC

Added after 3 minutes:

when i use preview_dft to list the reg,
i find almost all regs are ready to insert dft

do i understand right?

 

[rsqf]

chain test pattern failed contention checking

You should check the dft_drc report. The report will tell u the dft violation information such as D1.D2.D3.... . Then fix them

 

[HolySaint]

test coverage dft

You should check the dft_drc report. The report will tell u the dft violation information such as D1.D2.D3.... . Then fix them

thx , i'll have a try.
if more violation is found,fix the timing in dc script can help,is that right?

 

[rsqf]

dft+coverage

You should check the dft_drc report. The report will tell u the dft violation information such as D1.D2.D3.... . Then fix them

thx , i'll have a try.
if more violation is found,fix the timing in dc script can help,is that right?

if the dft script is correct , and autofix does not work , u should change the RTL code to improve the dft coverage.

 

[cheelgo]

dft_drc in dft

mostly the controllability and observability cause problem.
you could try to report scan chain cell.
what I impressed is that some part of design is not correctly inserted into scan chain.

 

[santhosh007]

dft violation

Warning: 1152726 faults aborted during contention prevention. (M139)

there is no pattern is generated becasue of the contention violation. i dont know how the DC is calculating cvoerage.

can you try in tetramax or fastscan to check the coverage estimation.
in tetramax, issue " run drc " command, this will give you the all the deatils to violations..

 

[HolySaint]

dft atpg script

thx for everyone
i'll try tmax to detect it again