ODR is inaccurate

[tdrellich]

I'm using the Arduino Nano 33 BLE Sense board. If in my setup I have:

IMU.setGyroFS(2);
IMU.setGyroODR(5);

IMU.setAccelFS(2);
IMU.setAccelODR(5);

I would expect the ODR of the accelerometer and gyro to be 476Hz. however the IMU.getAccelODR() and IMU.getGyroODR() commands return that I'm getting 469.61Hz. This wouldn't be particularly problematic, however, if I use the following loop:

float acc_x, acc_y, acc_z;
float total_acc_x = 0;
float total_acc_y = 0;
float total_acc_z = 0;
int n_acc_measurements = 0;

float gyro_p, gyro_q, gyro_r;
float total_p = 0;
float total_q = 0;
float total_r = 0;
int n_gyro_measurements = 0;

start_time = micros();
t = micros();

while (t - start_time < 3000000) {

        if (IMU.accelAvailable()){
            IMU.readRawAccel(acc_x, acc_y, acc_z);
            total_acc_x += acc_x;
            total_acc_y += acc_y;
            total_acc_z += acc_z;
            n_acc_measurements++;
        }

        if (IMU.gyroAvailable()){
            IMU.readRawGyro(gyro_p,gyro_q,gyro_r);
            total_p += gyro_p;
            total_q += gyro_q;
            total_r += gyro_r;
            n_gyro_measurements++;
        }
}

and then output n_acc_measurement / 3.0 and n_gyro_measurements / 3.0 I'm getting a frequency of 143.33Hz

[FemmeVerbeek]

You could have saved yourself writing this program, because it's already in the library. The functions getAccelODR() getGyroODR() and getMagnetODR() return the actual ODR value as was measured upon the last change in register settings. It is all explained in the documentation. Yes the original documentation is very inacurate about the actual odr values. That was the reason for doing it this way.