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TM4C123GH6PM: FPU calculations

Omar Emad
Prodigy 30 points
Part Number: TM4C123GH6PM

hello,

i have an issue using the FPU with keil uvision 5,

when i define a local variable the FPU calculations are done and i could see the results in the float registers, but the value of the declared variable remains 0,

but works just fine if it's a global variable, array,  or if i used the volatile keyword with local variables.

what i'm missing here?

  • 0
    TI__Guru 72500 points
    I am not familiar with the Keil compiler, but from your description it sounds as though it was not necessary to store the result in your local variable for the code to make the correct comparison and return the status. This is probably just the optimizer being efficient. Other than being able to examine the result in the local variable, is the function returning the correct response?
  • 0 in reply to Bob Crosby
    Prodigy 30 points

    Thanks,

    No the function doesn't return the correct response, and the optimization level is 0.

  • 0 in reply to Omar Emad
    TI__Guru 72500 points
    It is highly unlikely that this is a Cortex M4 FPU issue. If you think it is a coding problem, can you provide a small test case? If you think it is a compiler issue, you need to contact Keil.
  • 0 in reply to Bob Crosby
    Prodigy 30 points

    i followed the numbers through the FPU register and found out that it actually performs all the calculations in the code correctly and it actually returns the correct values they are just not available in the watch window for some reason, so i will contact Keil.

    Thanks for your help.