Hardware floating point on STM32F4

Andrei Chichak groups at chichak.ca
Fri Feb 21 23:32:53 UTC 2014

Hello gurus,

Something in Eclipse lead me to believe that I’m using soft float on my STM32F407 on my ST discovery board.

  #if (__FPU_PRESENT == 1) && (__FPU_USED == 1)

indicated that __FPU_USED was 0, and digging further lead me to the flag __SOFTFP__ is set. Hmmmm.

Putting in some cheesy float code showed that I was calling a bunch of aeabi float library code instead of chucking in the hardware floating point commands. I have defined __FPU_PRESENT=1, but I think I may need a differently compiled compiler.

The tools are running on my Mac and I put the whole thing together with Source Builder with the 4.11/rtems-arm.bset from Chris Johns about October 2013.

Question: How do I go about getting the C compiler to generate hardware floating point instructions? Load a different compiler (how), or just throw another compiler flag?

Thanks a bunch,


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