MPC5777C and STCU2_LB_PCSn limits

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MPC5777C and STCU2_LB_PCSn limits

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mauriziogreco
Contributor III

Hi, 

I'm searching information about value to be used for STCU2_LB_PCSn limits.

I found in the AN5288.pdf value for 90% of coverage. But I have not understand how values of that register can be modified in order to achive a different value of coverage.

Can I suppose linear relation must be used?

In other words: for example, in the application notes AN5288 is reported for STCU2_LB_PCS2 (3N45H) 0x500 for 90%, can I suppose value for 100% is equal 0x58E?  Is really so simple? Or we need to have another kind of details to modify % of coverage?

Thanks in advance for answer.

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petervlna
NXP Employee
NXP Employee

Hello,

Well, this is not so simple in my opinion. (I have never calculated coverage based on patterns)

RM states:

The percentage of the logic gates that will be tested during the BIST, known as the test coverage level, is determined by the number of patterns that are run on each partition. The number of patterns that are run is controlled by configuring the PCS bit-field in the STCU2_PCSn register. As the number of gates varies in each partition, the number of patterns required to achieve a determined level of coverage will also vary. The test level coverage achieved for the examples in the applications note meet at least 90% coverage of all logic in the logic partitions. Reducing the number of patterns run on a partition reduces the time taken to complete the BIST for that partition, but also reduces the coverage level. The pattern count for each partition is configured within the STCU.

Once you change PCS you need also to calculate new MISR values.

 If PCS values provided below are programmed into the STCU2 LBIST PC Stop Register
(STCU2_LB_PCSn), 90 percent of logic will be covered. Different PCS values will output different Multiple Input Signature
Register (MISR) values, which will affect LBIST passing criteria.

It is set to 90% in our application note, because automotive standard requires at least 90% to achieve certain ASIL level.

I am afraid that is not so simple to calculate the new coverage based on PCS and new MISR.

If you are still interested in how this is calculated I can ask internally.

regards,

Peter

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