Better Pedometer - HELP NEEDED!

M value? Acceleration magnitude?

Yes Magnitude.

We should really be doing the same stuff in the test harness.

Yes - need to be the same so we can do predicatble modelling that will match the real world measures when actually walking with the device etc.

I was not sure if the accelerometer chip does the calculation for magnitude OR the firmware does it. In the test harness I can see the In32_sqrt() function. Is this the same in the Bangle firmware. Was not sure where to look in the code.

Found this in ./libs/banglejs/jswrap_bangle.c

JsVar *jswrap_banglejs_getAccel() {
  JsVar *o = jsvNewObject();
  if (o) {
    jsvObjectSetChildAndUnLock(o, "x", jsvNewFromFloat(acc.x/8192.0));
    jsvObjectSetChildAndUnLock(o, "y", jsvNewFromFloat(acc.y/8192.0));
    jsvObjectSetChildAndUnLock(o, "z", jsvNewFromFloat(acc.z/8192.0));
    jsvObjectSetChildAndUnLock(o, "mag", jsvNewFromFloat(sqrt(accMagSquared)/8192.0));
    jsvObjectSetChildAndUnLock(o, "diff", jsvNewFromFloat(sqrt(accdiff)/8192.0));
  }
  return o;
}

Found this in
./targetlibs/nrf5x_15/external/micro-ecc/curve-specific.inc

static void mod_sqrt_default(uECC_word_t *a, uECC_Curve curve) {
  ...
}

Not really sure how this compares to:
Espruino/libs/misc/stepcount.c

// quick integer square root
// https://stackoverflow.com/questions/31117497/fastest-integer-square-root-in-the-least-amount-of-instructions
unsigned short int int_sqrt32(unsigned int x) {
  unsigned short int res=0;
  unsigned short int add= 0x8000;
  int i;
  for(i=0;i<16;i++) {
    unsigned short int temp=res | add;
    unsigned int g2=temp*temp;
    if (x>=g2)
      res=temp;
    add>>=1;
  }
  return res;
}

Apologies I think * is confusing the code formatter