I am currently on the fence in a debate regarding FPGA environmental testing (thermal cycling).
The question is, can the same FPGA stressed to the same thermal limits yield different results depending on how it is configured/programmed?
For example, data rates, data corruption, etc.
With something like a microcontroller I would say that regardless of how it is programmed the hardware remains the same, so its thermal properties will remain the same. FPGAs are a bit of a grey area, because although the configuration is described in code (i.e. HDL), it is creating a configuration in hardware within the FPGA.
Thoughts and opinions welcome, but if you have any relevant research papers or articles that would be great.
Edit: To add a bit of clarity, I will be more specific about the use case. The under test is a system control unit, where the main processor is an i.MX6 Arm CPU, with the main signal processing unit being an IGLOO2 FPGA. There are two builds of software available for it:
- Test control software, designed to stress it for design proving activities, but serves no purpose in the real world.
- Operational software, the software that will be shipped with the item
The argument is that because the environmental stress testing has been performed with the TCS there is a gap in our proving evidence because thermal cycling has not been performed using the software which it will be shipped with. The testing is performed in an environmental chamber which cycles between -40C and +70C. The counter argument is that the TCS is inherently designed to excessively stress the item, therefore the operational software should be fine.
The third argument thrown in to the mix is that regardless of the build of software, the hardware is the same, so the effects of external thermal stimuli should be the same.
Edit 2: Clearly I'm still struggling to explain myself. The product was designed internally but is being manufactured by a contractor in another country. The main qualification testing (environmental and EMC) is being performed by the contractor, however we are unable to ship them the 'real' software as it is restricted and cannot leave the country. With that in mind, we provided the contractor with technical requirements such as thermal environment, bus speeds, and a 'sanitized' functional requirements which were designed to be representative but without breaking restrictions. With this, they created their own software (a.k.a the TCS). The question I am asking is if the code is functionally representative but simply 'not the same' as the software that will ship with the product, then how much of a gap do we really have in our evidence?