Subversion Repositories FlightCtrl

#include <avr/io.h>

#include <avr/interrupt.h>

#include <avr/pgmspace.h>

#include "analog.h"

#include "attitude.h"

#include "sensors.h"

#include "printf_P.h"

#include "mk3mag.h"

// for Delay functions

#include "timer0.h"

// For reading and writing acc. meter offsets.

#include "eeprom.h"

// For debugOut

#include "output.h"

// set ADC enable & ADC Start Conversion & ADC Interrupt Enable bit

#define startADC() (ADCSRA |= (1<<ADEN)|(1<<ADSC)|(1<<ADIE))

const char* recal = ", recalibration needed.";

/*

 * For each A/D conversion cycle, each analog channel is sampled a number of times

 * (see array channelsForStates), and the results for each channel are summed.

 * Here are those for the gyros and the acc. meters. They are not zero-offset.

 * They are exported in the analog.h file - but please do not use them! The only

 * reason for the export is that the ENC-03_FC1.3 modules needs them for calibrating

 * the offsets with the DAC.

 */

volatile uint16_t sensorInputs[8];

int16_t acc[3];

int16_t filteredAcc[3] = { 0,0,0 };

/*

 * These 4 exported variables are zero-offset. The "PID" ones are used

 * in the attitude control as rotation rates. The "ATT" ones are for

 * integration to angles.

 */

int16_t gyro_PID[2];

int16_t gyro_ATT[2];

int16_t gyroD[2];

int16_t gyroDWindow[2][GYRO_D_WINDOW_LENGTH];

uint8_t gyroDWindowIdx = 0;

int16_t yawGyro;

int16_t magneticHeading;

int32_t groundPressure;

int16_t dHeight;

/*

 * Offset values. These are the raw gyro and acc. meter sums when the copter is

 * standing still. They are used for adjusting the gyro and acc. meter values

 * to be centered on zero.

 */

sensorOffset_t gyroOffset;

sensorOffset_t accOffset;

sensorOffset_t gyroAmplifierOffset;

/*

 * In the MK coordinate system, nose-down is positive and left-roll is positive.

 * If a sensor is used in an orientation where one but not both of the axes has

 * an opposite sign, PR_ORIENTATION_REVERSED is set to 1 (true).

 * Transform:

 * pitch <- pp*pitch + pr*roll

 * roll  <- rp*pitch + rr*roll

 * Not reversed, GYRO_QUADRANT:

 * 0: pp=1, pr=0, rp=0, rr=1  // 0    degrees

 * 1: pp=1, pr=-1,rp=1, rr=1  // +45  degrees

 * 2: pp=0, pr=-1,rp=1, rr=0  // +90  degrees

 * 3: pp=-1,pr=-1,rp=1, rr=1  // +135 degrees

 * 4: pp=-1,pr=0, rp=0, rr=-1 // +180 degrees

 * 5: pp=-1,pr=1, rp=-1,rr=-1 // +225 degrees

 * 6: pp=0, pr=1, rp=-1,rr=0  // +270 degrees

 * 7: pp=1, pr=1, rp=-1,rr=1  // +315 degrees

 * Reversed, GYRO_QUADRANT:

 * 0: pp=-1,pr=0, rp=0, rr=1  // 0    degrees with pitch reversed

 * 1: pp=-1,pr=-1,rp=-1,rr=1  // +45  degrees with pitch reversed

 * 2: pp=0, pr=-1,rp=-1,rr=0  // +90  degrees with pitch reversed

 * 3: pp=1, pr=-1,rp=-1,rr=1  // +135 degrees with pitch reversed

 * 4: pp=1, pr=0, rp=0, rr=-1 // +180 degrees with pitch reversed

 * 5: pp=1, pr=1, rp=1, rr=-1 // +225 degrees with pitch reversed

 * 6: pp=0, pr=1, rp=1, rr=0  // +270 degrees with pitch reversed

 * 7: pp=-1,pr=1, rp=1, rr=1  // +315 degrees with pitch reversed

 */

void rotate(int16_t* result, uint8_t quadrant, uint8_t reverse) {

  static const int8_t rotationTab[] = {1,1,0,-1,-1,-1,0,1};

  // Pitch to Pitch part

  int8_t xx = reverse ? rotationTab[(quadrant+4)%8] : rotationTab[quadrant];

  // Roll to Pitch part

  int8_t xy = rotationTab[(quadrant+2)%8];

  // Pitch to Roll part

  int8_t yx = reverse ? rotationTab[(quadrant+2)%8] : rotationTab[(quadrant+6)%8];

  // Roll to Roll part

  int8_t yy = rotationTab[quadrant];

  int16_t xIn = result[0];

  result[0] = xx*xIn + xy*result[1];

  result[1] = yx*xIn + yy*result[1];

  if (quadrant & 1) {

        // A rotation was used above, where the factors were too large by sqrt(2).

        // So, we multiply by 2^n/sqt(2) and right shift n bits, as to divide by sqrt(2).

        // A suitable value for n: Sample is 11 bits. After transformation it is the sum

        // of 2 11 bit numbers, so 12 bits. We have 4 bits left...

        result[0] = (result[0]*11) >> 4;

        result[1] = (result[1]*11) >> 4;

  }

}

/*

 * Air pressure

 */

volatile uint8_t rangewidth = 105;

// Direct from sensor, irrespective of range.

// volatile uint16_t rawAirPressure;

// Value of 2 samples, with range.

uint16_t simpleAirPressure;

// Value of AIRPRESSURE_OVERSAMPLING samples, with range, filtered.

int32_t filteredAirPressure;

#define MAX_D_AIRPRESSURE_WINDOW_LENGTH 32

//int32_t lastFilteredAirPressure;

int16_t dAirPressureWindow[MAX_D_AIRPRESSURE_WINDOW_LENGTH];

uint8_t dWindowPtr = 0;

#define MAX_AIRPRESSURE_WINDOW_LENGTH 32

int16_t airPressureWindow[MAX_AIRPRESSURE_WINDOW_LENGTH];

int32_t windowedAirPressure;

uint8_t windowPtr = 0;

// Partial sum of AIRPRESSURE_SUMMATION_FACTOR samples.

int32_t airPressureSum;

// The number of samples summed into airPressureSum so far.

uint8_t pressureMeasurementCount;

/*

 * Battery voltage, in units of: 1k/11k / 3V * 1024 = 31.03 per volt.

 * That is divided by 3 below, for a final 10.34 per volt.

 * So the initial value of 100 is for 9.7 volts.

 */

int16_t UBat = 100;

/*

 * Control and status.

 */

volatile uint16_t ADCycleCount = 0;

volatile uint8_t analogDataReady = 1;

/*

 * Experiment: Measuring vibration-induced sensor noise.

 */

uint16_t gyroNoisePeak[3];

uint16_t accNoisePeak[3];

volatile uint8_t adState;

volatile uint8_t adChannel;

// ADC channels

#define AD_GYRO_YAW       0

#define AD_GYRO_ROLL      1

#define AD_GYRO_PITCH     2

#define AD_AIRPRESSURE    3

#define AD_UBAT           4

#define AD_ACC_Z          5

#define AD_ACC_ROLL       6

#define AD_ACC_PITCH      7

/*

 * Table of AD converter inputs for each state.

 * The number of samples summed for each channel is equal to

 * the number of times the channel appears in the array.

 * The max. number of samples that can be taken in 2 ms is:

 * 20e6 / 128 / 13 / (1/2e-3) = 24. Since the main control

 * loop needs a little time between reading AD values and

 * re-enabling ADC, the real limit is (how much?) lower.

 * The acc. sensor is sampled even if not used - or installed

 * at all. The cost is not significant.

 */

const uint8_t channelsForStates[] PROGMEM = {

  AD_GYRO_PITCH, AD_GYRO_ROLL, AD_GYRO_YAW,

  AD_ACC_PITCH, AD_ACC_ROLL, AD_AIRPRESSURE,

  AD_GYRO_PITCH, AD_GYRO_ROLL, AD_ACC_Z, // at 8, measure Z acc.

  AD_GYRO_PITCH, AD_GYRO_ROLL, AD_GYRO_YAW, // at 11, finish yaw gyro

  AD_ACC_PITCH,   // at 12, finish pitch axis acc.

  AD_ACC_ROLL,    // at 13, finish roll axis acc.

  AD_AIRPRESSURE, // at 14, finish air pressure.

  AD_GYRO_PITCH,  // at 15, finish pitch gyro

  AD_GYRO_ROLL,   // at 16, finish roll gyro

  AD_UBAT         // at 17, measure battery.

};

// Feature removed. Could be reintroduced later - but should work for all gyro types then.

// uint8_t GyroDefectPitch = 0, GyroDefectRoll = 0, GyroDefectYaw = 0;

void analog_init(void) {

        uint8_t sreg = SREG;

        // disable all interrupts before reconfiguration

        cli();

        //ADC0 ... ADC7 is connected to PortA pin 0 ... 7

        DDRA = 0x00;

        PORTA = 0x00;

        // Digital Input Disable Register 0

        // Disable digital input buffer for analog adc_channel pins

        DIDR0 = 0xFF;

        // external reference, adjust data to the right

        ADMUX &= ~((1<<REFS1)|(1<<REFS0)|(1<<ADLAR));

        // set muxer to ADC adc_channel 0 (0 to 7 is a valid choice)

        ADMUX = (ADMUX & 0xE0);

        //Set ADC Control and Status Register A

        //Auto Trigger Enable, Prescaler Select Bits to Division Factor 128, i.e. ADC clock = SYSCKL/128 = 156.25 kHz

        ADCSRA = (1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0);

        //Set ADC Control and Status Register B

        //Trigger Source to Free Running Mode

        ADCSRB &= ~((1<<ADTS2)|(1<<ADTS1)|(1<<ADTS0));

        for (uint8_t i=0; i<MAX_AIRPRESSURE_WINDOW_LENGTH; i++) {

          airPressureWindow[i] = 0;

        }

    windowedAirPressure = 0;

        startAnalogConversionCycle();

        // restore global interrupt flags

        SREG = sreg;

}

uint16_t rawGyroValue(uint8_t axis) {

        return sensorInputs[AD_GYRO_PITCH-axis];

}

uint16_t rawAccValue(uint8_t axis) {

        return sensorInputs[AD_ACC_PITCH-axis];

}

void measureNoise(const int16_t sensor,

                volatile uint16_t* const noiseMeasurement, const uint8_t damping) {

        if (sensor > (int16_t) (*noiseMeasurement)) {

                *noiseMeasurement = sensor;

        } else if (-sensor > (int16_t) (*noiseMeasurement)) {

                *noiseMeasurement = -sensor;

        } else if (*noiseMeasurement > damping) {

                *noiseMeasurement -= damping;

        } else {

                *noiseMeasurement = 0;

        }

}

/*

 * Min.: 0

 * Max: About 106 * 240 + 2047 = 27487; it is OK with just a 16 bit type.

 */

uint16_t getSimplePressure(int advalue) {

        uint16_t result = (uint16_t) OCR0A * (uint16_t) rangewidth + advalue;

        result += (acc[Z] * (staticParams.airpressureAccZCorrection-128)) >> 10;

        return result;

}

void startAnalogConversionCycle(void) {

  analogDataReady = 0;

  // Stop the sampling. Cycle is over.

  for (uint8_t i = 0; i < 8; i++) {

    sensorInputs[i] = 0;

  }

  adState = 0;

  adChannel = AD_GYRO_PITCH;

  ADMUX = (ADMUX & 0xE0) | adChannel;

  startADC();

}

/*****************************************************

 * Interrupt Service Routine for ADC

 * Runs at 312.5 kHz or 3.2 �s. When all states are

 * processed further conversions are stopped.

 *****************************************************/

ISR(ADC_vect) {

  sensorInputs[adChannel] += ADC;

  // set up for next state.

  adState++;

  if (adState < sizeof(channelsForStates)) {

    adChannel = pgm_read_byte(&channelsForStates[adState]);

    // set adc muxer to next adChannel

    ADMUX = (ADMUX & 0xE0) | adChannel;

    // after full cycle stop further interrupts

    startADC();

  } else {

    ADCycleCount++;

    analogDataReady = 1;

    // do not restart ADC converter. 

  }

}

// Experimental gyro shake takeoff detect!

uint16_t gyroActivity = 0;

void measureGyroActivityAndUpdateGyro(uint8_t axis, int16_t newValue) {

  int16_t tmp = gyro_ATT[axis];

  gyro_ATT[axis] = newValue;

  tmp -= newValue;

  tmp = (tmp*tmp) >> 4;

  if (gyroActivity + (uint16_t)tmp < 0x8000)

    gyroActivity += tmp;

}

#define GADAMPING 10

void dampenGyroActivity(void) {

  uint32_t tmp = gyroActivity;

  tmp *= ((1<<GADAMPING)-1);

  tmp >>= GADAMPING;

  gyroActivity = tmp;

}

void analog_updateGyros(void) {

  // for various filters...

  int16_t tempOffsetGyro[2], tempGyro;

  debugOut.digital[0] &= ~DEBUG_SENSORLIMIT;

  for (uint8_t axis=0; axis<2; axis++) {

    tempGyro = rawGyroValue(axis);

    /*

     * Process the gyro data for the PID controller.

     */

    // 1) Extrapolate: Near the ends of the range, we boost the input significantly. This simulates a

    //    gyro with a wider range, and helps counter saturation at full control.

    if (staticParams.bitConfig & CFG_GYRO_SATURATION_PREVENTION) {

      if (tempGyro < SENSOR_MIN_PITCHROLL) {

                debugOut.digital[0] |= DEBUG_SENSORLIMIT;

                tempGyro = tempGyro * EXTRAPOLATION_SLOPE - EXTRAPOLATION_LIMIT;

      } else if (tempGyro > SENSOR_MAX_PITCHROLL) {

                debugOut.digital[0] |= DEBUG_SENSORLIMIT;

                tempGyro = (tempGyro - SENSOR_MAX_PITCHROLL) * EXTRAPOLATION_SLOPE + SENSOR_MAX_PITCHROLL;

      }

    }

    // 2) Apply sign and offset, scale before filtering.

    tempOffsetGyro[axis] = (tempGyro - gyroOffset.offsets[axis]) * GYRO_FACTOR_PITCHROLL;

  }

  // 2.1: Transform axes.

  rotate(tempOffsetGyro, staticParams.gyroQuadrant, staticParams.imuReversedFlags & IMU_REVERSE_GYRO_PR);

  for (uint8_t axis=0; axis<2; axis++) {

        // 3) Filter.

    tempOffsetGyro[axis] = (gyro_PID[axis] * (staticParams.gyroPIDFilterConstant - 1) + tempOffsetGyro[axis]) / staticParams.gyroPIDFilterConstant;

    // 4) Measure noise.

    measureNoise(tempOffsetGyro[axis], &gyroNoisePeak[axis], GYRO_NOISE_MEASUREMENT_DAMPING);

    // 5) Differential measurement.

    // gyroD[axis] = (gyroD[axis] * (staticParams.gyroDFilterConstant - 1) + (tempOffsetGyro[axis] - gyro_PID[axis])) / staticParams.gyroDFilterConstant;

    int16_t diff = tempOffsetGyro[axis] - gyro_PID[axis];

    gyroD[axis] -= gyroDWindow[axis][gyroDWindowIdx];

    gyroD[axis] += diff;

    gyroDWindow[axis][gyroDWindowIdx] = diff;

    // 6) Done.

    gyro_PID[axis] = tempOffsetGyro[axis];

    // Prepare tempOffsetGyro for next calculation below...

    tempOffsetGyro[axis] = (rawGyroValue(axis) - gyroOffset.offsets[axis]) * GYRO_FACTOR_PITCHROLL;

  }

  if (gyroDWindowIdx >= GYRO_D_WINDOW_LENGTH) {

          gyroDWindowIdx = 0;

  }

  /*

   * Now process the data for attitude angles.

   */

   rotate(tempOffsetGyro, staticParams.gyroQuadrant, staticParams.imuReversedFlags & IMU_REVERSE_GYRO_PR);

   measureGyroActivityAndUpdateGyro(0, tempOffsetGyro[PITCH]);

   measureGyroActivityAndUpdateGyro(1, tempOffsetGyro[ROLL]);

   dampenGyroActivity();

  // Yaw gyro.

  if (staticParams.imuReversedFlags & IMU_REVERSE_GYRO_YAW)

    yawGyro = gyroOffset.offsets[YAW] - sensorInputs[AD_GYRO_YAW];

  else

    yawGyro = sensorInputs[AD_GYRO_YAW] - gyroOffset.offsets[YAW];

}

void analog_updateAccelerometers(void) {

  // Pitch and roll axis accelerations.

  for (uint8_t axis=0; axis<2; axis++) {

    acc[axis] = rawAccValue(axis) - accOffset.offsets[axis];

  }

  rotate(acc, staticParams.accQuadrant, staticParams.imuReversedFlags & IMU_REVERSE_ACC_XY);

  for(uint8_t axis=0; axis<3; axis++) {

    filteredAcc[axis] = (filteredAcc[axis] * (staticParams.accFilterConstant - 1) + acc[axis]) / staticParams.accFilterConstant;

    measureNoise(acc[axis], &accNoisePeak[axis], 1);

  }

  // Z acc.

  if (staticParams.imuReversedFlags & 8)

    acc[Z] = accOffset.offsets[Z] - sensorInputs[AD_ACC_Z];

  else

    acc[Z] = sensorInputs[AD_ACC_Z] - accOffset.offsets[Z];

  debugOut.analog[29] = acc[Z];

}

void analog_updateAirPressure(void) {

  static uint16_t pressureAutorangingWait = 25;

  uint16_t rawAirPressure;

  int16_t newrange;

  // air pressure

  if (pressureAutorangingWait) {

    //A range switch was done recently. Wait for steadying.

    pressureAutorangingWait--;

  } else {

    rawAirPressure = sensorInputs[AD_AIRPRESSURE];

    if (rawAirPressure < MIN_RAWPRESSURE) {

      // value is too low, so decrease voltage on the op amp minus input, making the value higher.

      newrange = OCR0A - (MAX_RAWPRESSURE - MIN_RAWPRESSURE) / (rangewidth * 4); // 4; // (MAX_RAWPRESSURE - rawAirPressure) / (rangewidth * 2) + 1;

      if (newrange > MIN_RANGES_EXTRAPOLATION) {

        pressureAutorangingWait = (OCR0A - newrange) * AUTORANGE_WAIT_FACTOR; // = OCRA0 - OCRA0 +

        OCR0A = newrange;

      } else {

        if (OCR0A) {

          OCR0A--;

          pressureAutorangingWait = AUTORANGE_WAIT_FACTOR;

        }

      }

    } else if (rawAirPressure > MAX_RAWPRESSURE) {

      // value is too high, so increase voltage on the op amp minus input, making the value lower.

      // If near the end, make a limited increase

      newrange = OCR0A + (MAX_RAWPRESSURE - MIN_RAWPRESSURE) / (rangewidth * 4); // 4;  // (rawAirPressure - MIN_RAWPRESSURE) / (rangewidth * 2) - 1;

      if (newrange < MAX_RANGES_EXTRAPOLATION) {

        pressureAutorangingWait = (newrange - OCR0A) * AUTORANGE_WAIT_FACTOR;

        OCR0A = newrange;

      } else {

        if (OCR0A < 254) {

          OCR0A++;

          pressureAutorangingWait = AUTORANGE_WAIT_FACTOR;

        }

      }

    }

    // Even if the sample is off-range, use it.

    simpleAirPressure = getSimplePressure(rawAirPressure);

    debugOut.analog[6] = rawAirPressure;

    debugOut.analog[7] = simpleAirPressure;

    if (simpleAirPressure < MIN_RANGES_EXTRAPOLATION * rangewidth) {

      // Danger: pressure near lower end of range. If the measurement saturates, the

      // copter may climb uncontrolledly... Simulate a drastic reduction in pressure.

      debugOut.digital[1] |= DEBUG_SENSORLIMIT;

      airPressureSum += (int16_t) MIN_RANGES_EXTRAPOLATION * rangewidth

        + (simpleAirPressure - (int16_t) MIN_RANGES_EXTRAPOLATION

           * rangewidth) * PRESSURE_EXTRAPOLATION_COEFF;

    } else if (simpleAirPressure > MAX_RANGES_EXTRAPOLATION * rangewidth) {

      // Danger: pressure near upper end of range. If the measurement saturates, the

      // copter may descend uncontrolledly... Simulate a drastic increase in pressure.

      debugOut.digital[1] |= DEBUG_SENSORLIMIT;

      airPressureSum += (int16_t) MAX_RANGES_EXTRAPOLATION * rangewidth

        + (simpleAirPressure - (int16_t) MAX_RANGES_EXTRAPOLATION

           * rangewidth) * PRESSURE_EXTRAPOLATION_COEFF;

    } else {

      // normal case.

      // If AIRPRESSURE_OVERSAMPLING is an odd number we only want to add half the double sample.

      // The 2 cases above (end of range) are ignored for this.

      debugOut.digital[1] &= ~DEBUG_SENSORLIMIT;

          airPressureSum += simpleAirPressure;

    }

    // 2 samples were added.

    pressureMeasurementCount += 2;

    // Assumption here: AIRPRESSURE_OVERSAMPLING is even (well we all know it's 14 haha...)

    if (pressureMeasurementCount == AIRPRESSURE_OVERSAMPLING) {

      // The best oversampling count is 14.5. We add a quarter of the double ADC value to get the final half.

      airPressureSum += simpleAirPressure >> 2;

      uint32_t lastFilteredAirPressure = filteredAirPressure;

      if (!staticParams.airpressureWindowLength) {

          filteredAirPressure = (filteredAirPressure * (staticParams.airpressureFilterConstant - 1)

                          + airPressureSum + staticParams.airpressureFilterConstant / 2) / staticParams.airpressureFilterConstant;

      } else {

          // use windowed.

          windowedAirPressure += simpleAirPressure;

          windowedAirPressure -= airPressureWindow[windowPtr];

          airPressureWindow[windowPtr++] = simpleAirPressure;

          if (windowPtr >= staticParams.airpressureWindowLength) windowPtr = 0;

          filteredAirPressure = windowedAirPressure / staticParams.airpressureWindowLength;

      }

      // positive diff of pressure

      int16_t diff = filteredAirPressure - lastFilteredAirPressure;

      // is a negative diff of height.

      dHeight -= diff;

      // remove old sample (fifo) from window.

      dHeight += dAirPressureWindow[dWindowPtr];

      dAirPressureWindow[dWindowPtr++] = diff;

      if (dWindowPtr >= staticParams.airpressureDWindowLength) dWindowPtr = 0;

      pressureMeasurementCount = airPressureSum = 0;

    }

  }

}

void analog_updateBatteryVoltage(void) {

  // Battery. The measured value is: (V * 1k/11k)/3v * 1024 = 31.03 counts per volt (max. measurable is 33v).

  // This is divided by 3 --> 10.34 counts per volt.

  UBat = (3 * UBat + sensorInputs[AD_UBAT] / 3) / 4;

}

void analog_update(void) {

  analog_updateGyros();

  analog_updateAccelerometers();

  analog_updateAirPressure();

  analog_updateBatteryVoltage();

#ifdef USE_MK3MAG

  magneticHeading = volatileMagneticHeading;

#endif

}

void analog_setNeutral() {

  gyro_init();

  if (gyroOffset_readFromEEProm()) {

    printf("gyro offsets invalid%s",recal);

    gyroOffset.offsets[PITCH] = gyroOffset.offsets[ROLL] = 512 * GYRO_OVERSAMPLING_PITCHROLL;

    gyroOffset.offsets[YAW] = 512 * GYRO_OVERSAMPLING_YAW;

  }

  if (accOffset_readFromEEProm()) {

    printf("acc. meter offsets invalid%s",recal);

    accOffset.offsets[PITCH] = accOffset.offsets[ROLL] = 512 * ACC_OVERSAMPLING_XY;

    accOffset.offsets[Z] = 717 * ACC_OVERSAMPLING_Z;

  }

  // Noise is relative to offset. So, reset noise measurements when changing offsets.

  for (uint8_t i=PITCH; i<=ROLL; i++) {

          gyroNoisePeak[i] = 0;

          accNoisePeak[i] = 0;

          gyroD[i] = 0;

          for (uint8_t j=0; j<GYRO_D_WINDOW_LENGTH; j++) {

                  gyroDWindow[i][j] = 0;

          }

  }

  // Setting offset values has an influence in the analog.c ISR

  // Therefore run measurement for 100ms to achive stable readings

  delay_ms_with_adc_measurement(100, 0);

  gyroActivity = 0;

}

void analog_calibrateGyros(void) {

#define GYRO_OFFSET_CYCLES 32

  uint8_t i, axis;

  int32_t offsets[3] = { 0, 0, 0 };

  gyro_calibrate();

  // determine gyro bias by averaging (requires that the copter does not rotate around any axis!)

  for (i = 0; i < GYRO_OFFSET_CYCLES; i++) {

    delay_ms_with_adc_measurement(10, 1);

    for (axis = PITCH; axis <= YAW; axis++) {

      offsets[axis] += rawGyroValue(axis);

    }

  }

  for (axis = PITCH; axis <= YAW; axis++) {

    gyroOffset.offsets[axis] = (offsets[axis] + GYRO_OFFSET_CYCLES / 2) / GYRO_OFFSET_CYCLES;

    int16_t min = (512-200) * (axis==YAW) ? GYRO_OVERSAMPLING_YAW : GYRO_OVERSAMPLING_PITCHROLL;

    int16_t max = (512+200) * (axis==YAW) ? GYRO_OVERSAMPLING_YAW : GYRO_OVERSAMPLING_PITCHROLL;

    if(gyroOffset.offsets[axis] < min || gyroOffset.offsets[axis] > max)

      versionInfo.hardwareErrors[0] |= FC_ERROR0_GYRO_PITCH << axis;

  }

  gyroOffset_writeToEEProm();  

  startAnalogConversionCycle();

}

/*

 * Find acc. offsets for a neutral reading, and write them to EEPROM.

 * Does not (!} update the local variables. This must be done with a

 * call to analog_calibrate() - this always (?) is done by the caller

 * anyway. There would be nothing wrong with updating the variables

 * directly from here, though.

 */

void analog_calibrateAcc(void) {

#define ACC_OFFSET_CYCLES 32

  uint8_t i, axis;

  int32_t offsets[3] = { 0, 0, 0 };

  for (i = 0; i < ACC_OFFSET_CYCLES; i++) {

    delay_ms_with_adc_measurement(10, 1);

    for (axis = PITCH; axis <= YAW; axis++) {

      offsets[axis] += rawAccValue(axis);

    }

  }

  for (axis = PITCH; axis <= YAW; axis++) {

    accOffset.offsets[axis] = (offsets[axis] + ACC_OFFSET_CYCLES / 2) / ACC_OFFSET_CYCLES;

    int16_t min,max;

    if (axis==Z) {

        if (staticParams.imuReversedFlags & IMU_REVERSE_ACC_Z) {

        // TODO: This assumes a sensitivity of +/- 2g.

                min = (256-200) * ACC_OVERSAMPLING_Z;

                        max = (256+200) * ACC_OVERSAMPLING_Z;

        } else {

        // TODO: This assumes a sensitivity of +/- 2g.

                min = (768-200) * ACC_OVERSAMPLING_Z;

                        max = (768+200) * ACC_OVERSAMPLING_Z;

        }

    } else {

        min = (512-200) * ACC_OVERSAMPLING_XY;

        max = (512+200) * ACC_OVERSAMPLING_XY;

    }

    if(gyroOffset.offsets[axis] < min || gyroOffset.offsets[axis] > max) {

      versionInfo.hardwareErrors[0] |= FC_ERROR0_ACC_X << axis;

    }

  }

  accOffset_writeToEEProm();

  startAnalogConversionCycle();

}

void analog_setGround() {

  groundPressure = filteredAirPressure;

}

int32_t analog_getHeight(void) {

  return groundPressure - filteredAirPressure;

}

int16_t analog_getDHeight(void) {

  return dHeight;

}