Electronic – STM32F4 – Floating point unit ( FPU )

If you want to do it yourself, I'd say just do it.

I guess you wont find too many resources or tutorial because there is not much to it.

Here is an outline:

• adding/subtracting:
  if exponents differ too much (more than the mantissa has bits):
  just return the value with larger exponent (if this is the subtrahend: negate)

  if exponents are similar:
  shift the mantissa of smaller value by difference of exponents and add to/subtract from other mantissa (using fixed point arithmetic)
  if result is not 0: shift mantissa up until MSBit of result is 1 and decrement exponent the same amount

• multiplication/division:
  multiply/divide mantissas (using fixed point arithmetic) and add/subtract exponents

Why don't you try to remove all the floating point calculations from the interrupt service routines. Many folks would point out that it shouldn't be in there in the first place.

Pre-calculate floating point things in the mainline code flow so that it does not need to be in the ISR. This may require some rethinking of the algorithms used but will often lead to more robust and leaner code.