floating point operations with and without Custom instruction floating point hardware

Sorry I thought you were connecting your own FPU to the processor. I didn't notice it at first but I think Kevin is right. The compiler is probably performing the calculation at compile time which would explain the run times are identical. You'll need to specify your variables as volatile to make sure they are not optimized away but I don't think that will prevent the compiler from performing the multiplications at compile time. If you assign A and B into variable and then perform the calculation then you should have the multiplies occuring at run time (using the volatile keyword as well)