Mentor tessent MBIST for ROM problem

Dear all:
I am performing MBIST by Tessent. There are several RAM and ROM in my design. When running ETPlan, a warning message showed " NonProgrammable MemoryBist (...) wrapper has RomDiagnostic disabled. The ROM Diagnostic hardware will not be generated." Can any MBIST expert explain this warning for me? Is it mean that my ROMs will not be tested?

By the way, my ROM content will be changed in the future. How the MBIST hardware tests the ROM if the ROM content are changed by mental changing?

Thank you for your reply.

I'm not an MBIST expert and I haven't used ETPlanner either, but only Tessent MBIST Architect to generate the BISTs for RAMs. So I'm not very sure what's happening with the ROM. I read in one of the manuals that you need to have separate controllers for RAMs and ROMs, that means you need two generation steps. Have you gone through the reference manuals to figure out the problem? There's a description of how to do MBIST for ROMs in MBIST process guide document.

Anyways what I believe is happening here is maybe you haven't enabled the diagnostics mode for the ROMs in your design. I feel it is ok if you don't want to have any diagnostics run upon an MBIST failure or if you are tight on area and don't want to introduce extra hardware.

Hello, Harpv:
Thank you for your reply. I perform MBIST step by step according to the tool guide. I didn't see the guide mentioned any different in handling ROM. I supposed that Tessent shall separate controller by itself if I follow the steps.

Do you know what the function "ROM diagnostic hardware" is? And do you have any ideal about my 2nd questions?

Diagnostic hardware will help you debug in case of a BIST failure.

In the generation phase you can specify whether you want the generated BIST to have a diagnostic feature.

Once you have generated with the diagnostics hardware then you'll have two options to do your BIST runs i.e. 1) with or 2) without diagnostics enabled. If you run with the diagnostics enabled then you'll be able to gather additional information about a particular failure like the memory bank or the address at which the test failed etc.

I'm sorry, I don't know the answer to your second question.