Cortex M7 DSP moving average UMAAL


I am looking to do a moving average function using DSP instructions of ARM Cortex M7. Unfortunately I couldn't find a direct example. My goal is to have variables for

- the sum

- the new value

- the oldest value

Then the algorithm is sum = sum + new value - oldest value and average = sum / ( number of values between oldest and new), ie two instructions

I think instruction UMAAL could be good for this, I found it in instruction set summary, but it is not in CMSIS library. Why is that? Where can I find details about it and how can I create my own C asm caller?

Thanks for any help and hints or other ideas on this topic, I hope it also helps other developers.

Kind regards


(I posted this also in Processor discussions, because I missed the embedded forum. Please delete it there, thanks)

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  • Optimised as you describe, yields the same division, where an optimising compiler should choose the optimal implementation based on it being able to deduce that WINDOW is a constant, and the particular characteristics of the operand types;

    #include <stdint.h>
    #define WINDOW 73
    typedef uint16_t sample_t;
    typedef uint32_t accum_t;
    sample_t samples[WINDOW];
    accum_t sum;
    unsigned int position;
    sample_t add_and_get_average(sample_t sample)
      if(position >= WINDOW)
        position = 0;
      sum -= samples[position];
      sum += sample;
      samples[position] = sample;
      return sum / WINDOW;


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