should the scan chain include the mbist logic?

[ljwfred]

should the scan chain include the mbist logic?

in mbist logic some registers control the clock selection.
during the scan insertion, the control registers are added to the scan chain.

and in scan mode, while shifting, the control registers' Q ports are toggling and make the clock sometimes disable.

i have to change the netlist mannually.

it is really disturbing.

if the mbist logic is not added to the chain, i think this kind of trouble will not happen.

scan is used for testing the function, should the mbist invoved?? :???::???::???::???:

thanks

 

[yx.yang]

Ok, let's analysis each case:
1): include MBIST logic in the scan chain. If both MBIST and scan pass, then you think this chip works.
2): exclude MBIST in the scan chain. MBIST logic can't be tested by scan. But if there is some defect in the MBIST logic, do you think it can pass MBIST test?
So, I think exclude MBIST logic in SCAN chain is ok.

 

[rca]

You could only not included the flop which will impact the clock or add the logic in the rtl code to ignore the mbist when the scan is enable for example.

 

[ljwfred]

Hi yang,

if the mbist is included in the scan chain, while scan pattern includes the mbist register failed, and then we dont need to do the mbist test.

does it make any sense?

thanks

- - - Updated - - -

hi, rca
yes, what i am doing now is adding an and logic to the clock select port, in order to avoid the control signal changing.

do you mean we have to include the mbist in to scan chain?
can you provide me some reasons?

thanks

 

[rca]

Yes you could add the mbist in the Spain chain to be covered.

 

[yx.yang]

Hi yang,

if the mbist is included in the scan chain, while scan pattern includes the mbist register failed, and then we dont need to do the mbist test.

does it make any sense?

thanks

I think whether or not you include the MBIST logic in the scan chain are all ok. Now you have problem with the scan chain if you want to include the MBIST. I think you can just ignore the MBIST. If you have time, I also prefer you debug out why this is some issue and how to fix it.
In our previous project, we exclude the MBIST logic in the scan chain.
Thanks