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Hi,
I am at the moment testing a Cortex M3 (Evaluation Board with Toshiba TMPM330). I am thinking about realising a controller on it in combination with the RTX-RL OS. This requires massive usage of filters as well as differentiation.
Usually, building this thing in university, I can simply use floating points and everything is fine. Due to the fact that the Cortex M3 only emulates floating point operations, I do wonder if this causes massive performance issues and if there are any other limitation. Using it with usually integers or similiar is not really a great alternative.
Has anyone experience and can recommend me ideas? Is it fine if I just use the floating point code, can I avoid some issues by simple adjustments or do I have to code it in fixed point.
Thank you
Christian
Is there just a rule of thumb a la multiplication in floating takes 5x the time of fixed point operations? I can be very rough that's fine for me. Just to get an idea.
I did a quick test for you:
volatile int i[3] = { 1, 2, 3 }; volatile float f[3] = ( 1, 2, 3 }; int main(void) { i[0] = i[1] * i[2]; f[0] = f[1] * f[2]; }
The integer multiplication took 7 cycles, of which 4 cycles were used to load operands and 2 cycles - to store the result. The multiplication itself is 1 cycle, in accordance with 'hardware single-cycle multiply' promise of Cortex-M3. The float multiplication took 47 cycles with the multiplication itself taking 41 cycles. Keep in mind that the float multiplication execution time depends on the values of operands.