Resource allocation problems in Software DFMEA

[Cephissus]

Dear all,

While working on Software FMEAs we realized that each piece of software made certain use of common resources: Execution time, RAM, ROM, etc...

If a failure of a characteristic of that piece of software is defined as:

Execution time is too long​

Its mother function will only fail in a way that it will take too long to execute, but most importantly that means that many of the other functions that were supposed to be performed in the same time lapse will simply not be executed at all. So we defined the following failure for these other functions:

Cannot be executed because of lack of resources​

So now, as we are working with APIS for example, and building a failure net in which each function taking too long results in the other functions not being able to execute, we can have for N functions, N*N failure net links and it will become a big spaghetti dish...

Would you maybe know of any other nice and more practical way to handle this?

 

[yodon]

A little difficult to fully engage on this one without a better understanding of the application and internals; however, it sounds like the Risk Management exercise revealed that the architecture cannot support the application as intended. Building a failure net seems to be more of an effort to mask the problem instead of eliminating the root cause.

 

[Cephissus]

Note: This question is strongly related to VDA System FMEA methodologies and the usage of APIS as a software.

Well we are doing the FMEA before starting the design, so at this moment we don't know whether the ROM capacity will be large enough to store all the software.

However at the root cause level of the software code, we have a System Element containing the Product Characteristic "ROM size". We also have the failure "ROM Size too big".

This would lead not to a function failure (for ex: Software not running properly), but to a compilation problem: Software can't be compiled.

So what I am wondering is whether I should enter this last entry, and what would be it's related function? Could it be that each software has a function "Shall be compilable?"

 

[yodon]

[QUOTE="So what I am wondering is whether I should enter this last entry, and what would be it's related function? Could it be that each software has a function "Shall be compilable?"[/QUOTE]

Hmm... that doesn't sound all that useful. If it doesn't compile, you don't have a system. And even if something can be compiled, that's certainly no indication of 'goodness.'

 

[tomshoup]

Cephissus on Jan 17 mentioned "we are doing the FMEA before starting the design." You can only do FMEA on an existing design or perhaps a conceptual design. But this is where Fault Tree Analysis might be better because it would lead you to the risk of ROM being sized wrong. In general FTA is a design tool and FMEA is an analysis tool.