Add motion tracking and calibration features

source/imu.h

@@ -4,8 +4,27 @@
 
 extern LSM6DS3 imu;
 
+// Sensor configuration used by the tracking pipeline.
+// Gyro ±1000 dps (35 mdps/LSB): fine enough that quantisation sits below the
+// sensor noise floor, while hand flicks never saturate. Accel ±4 g.
+// Every sample is read from the hardware FIFO, so integration uses the sensor's
+// own sample clock instead of loop timing, and nothing is lost when the loop stalls.
+constexpr float IMU_ODR_HZ        = 208.0f;
+constexpr float IMU_DT            = 1.0f / IMU_ODR_HZ;
+constexpr float GYRO_DPS_PER_LSB  = 0.035f;
+constexpr float GYRO_RAD_PER_LSB  = GYRO_DPS_PER_LSB * (PI / 180.0f);
+constexpr float ACCEL_G_PER_LSB   = 0.000122f;
+
+struct ImuRaw { int16_t gx, gy, gz, ax, ay, az; };
+
+extern uint32_t imuFifoOverruns;
+extern uint32_t imuI2cErrors;
+
 void imuWriteReg(uint8_t reg, uint8_t val);
 uint8_t imuReadReg(uint8_t reg);
+void imuConfigure();
+void imuFifoReset();
+int  imuReadFifo(ImuRaw* out, int maxSamples);
 float readIMUTemp();
 void calibrateGyroBias();
 float applyCurve(float v);