Core Self Test FPU

[Daniel Stang]

Posted on September 07, 2017 at 13:04

Hello,

to achieve a SIL2 by using a STM32F4 MCU a periodical core self-test is required. So the CPU itself and the FPU shall be tested. STM is giving us the manual 'UM1840: STM32F4 series safety manual'

 (

http://www.st.com/en/embedded-software/stm32-safesil.html

).

At Chapter 3.6.1 it is said that:

'Permanent faults affecting the CPU Core ARM

�

Cortex

�

-M4 (including also the FPU) are addressed through a dedicated software test executing a sequence of instructions and data Transfers.'

Also STM is giving us the Software 'STM32-CLASSB-SPL' to achieve a safe MCU and its periphals.

(

http://www.st.com/content/st_com/en/products/embedded-software/mcus-embedded-software/stm32-embedded-software/stm32-standard-peripheral-libraries-expansions/stm32-classb-spl.html

)

I can't find the part regarding the FPU self-test.

Do i miss something?

Is it possible to test a FPU and get a adequat diagnostic coverage?

Im thankful for any help,

Daniel

#core-self-test #fpu #sil #stm32f4 #safety #iec61508

[Tesla DeLorean]

Posted on September 07, 2017 at 17:40

Most of this safety stuff is entirely superficial...

The FPU has very basic function, it doesn't support transcendental or algorithmic implementations.

Check the registers hold content, run through the basic add, multiplication, division, root, across multiple registers, holding intermediate results across a chain of computations, you should have a pretty high degree of coverage and protection against stuck-at faults or data path issues. ie failure will compound readily and apparently.

Stuff in initial data, grind through the test sequence, check terminal data.

[Daniel Stang]

Posted on September 08, 2017 at 07:42

Thanks Clive,

so am i rigth that STM hasnt implemented a FPU self-test routine in their safety software package?

Is there some example available?

And last STM gives us a functional safety manual to achieve IEC 61508 Safety Integrity Level (SIL2/3) certification with STM32. But the Software on this side (first link) claims that you achieve only IEC60335. So you need to implement further more operations to be conform with the 61508?