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MagneticSensorI2C.cpp
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MagneticSensorI2C.cpp
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#include "MagneticSensorI2C.h"
/** Typical configuration for the 12bit AMS AS5600 magnetic sensor over I2C interface */
MagneticSensorI2CConfig_s AS5600_I2C = {
.chip_address = 0x36,
.bit_resolution = 12,
.angle_register = 0x0E,
.data_start_bit = 11
};
/** Typical configuration for the 12bit AMS AS5048 magnetic sensor over I2C interface */
MagneticSensorI2CConfig_s AS5048_I2C = {
.chip_address = 0x40, // highly configurable. if A1 and A2 are held low, this is probable value
.bit_resolution = 14,
.angle_register = 0xFE,
.data_start_bit = 15
};
// MagneticSensorI2C(uint8_t _chip_address, float _cpr, uint8_t _angle_register_msb)
// @param _chip_address I2C chip address
// @param _bit_resolution bit resolution of the sensor
// @param _angle_register_msb angle read register
// @param _bits_used_msb number of used bits in msb
MagneticSensorI2C::MagneticSensorI2C(uint8_t _chip_address, int _bit_resolution, uint8_t _angle_register_msb, int _bits_used_msb){
// chip I2C address
chip_address = _chip_address;
// angle read register of the magnetic sensor
angle_register_msb = _angle_register_msb;
// register maximum value (counts per revolution)
cpr = pow(2, _bit_resolution);
// depending on the sensor architecture there are different combinations of
// LSB and MSB register used bits
// AS5600 uses 0..7 LSB and 8..11 MSB
// AS5048 uses 0..5 LSB and 6..13 MSB
// used bits in LSB
lsb_used = _bit_resolution - _bits_used_msb;
// extraction masks
lsb_mask = (uint8_t)( (2 << lsb_used) - 1 );
msb_mask = (uint8_t)( (2 << _bits_used_msb) - 1 );
wire = &Wire;
}
MagneticSensorI2C::MagneticSensorI2C(MagneticSensorI2CConfig_s config){
chip_address = config.chip_address;
// angle read register of the magnetic sensor
angle_register_msb = config.angle_register;
// register maximum value (counts per revolution)
cpr = pow(2, config.bit_resolution);
int bits_used_msb = config.data_start_bit - 7;
lsb_used = config.bit_resolution - bits_used_msb;
// extraction masks
lsb_mask = (uint8_t)( (2 << lsb_used) - 1 );
msb_mask = (uint8_t)( (2 << bits_used_msb) - 1 );
wire = &Wire;
}
void MagneticSensorI2C::init(TwoWire* _wire){
wire = _wire;
// I2C communication begin
wire->begin();
// velocity calculation init
angle_prev = 0;
velocity_calc_timestamp = _micros();
// full rotations tracking number
full_rotation_offset = 0;
angle_data_prev = getRawCount();
zero_offset = 0;
}
// Shaft angle calculation
// angle is in radians [rad]
float MagneticSensorI2C::getAngle(){
// raw data from the sensor
float angle_data = getRawCount();
// tracking the number of rotations
// in order to expand angle range form [0,2PI]
// to basically infinity
float d_angle = angle_data - angle_data_prev;
// if overflow happened track it as full rotation
if(abs(d_angle) > (0.8*cpr) ) full_rotation_offset += d_angle > 0 ? -_2PI : _2PI;
// save the current angle value for the next steps
// in order to know if overflow happened
angle_data_prev = angle_data;
// zero offset adding
angle_data -= (int)zero_offset;
// return the full angle
// (number of full rotations)*2PI + current sensor angle
return natural_direction * (full_rotation_offset + ( angle_data / (float)cpr) * _2PI);
}
// Shaft velocity calculation
float MagneticSensorI2C::getVelocity(){
// calculate sample time
unsigned long now_us = _micros();
float Ts = (now_us - velocity_calc_timestamp)*1e-6;
// quick fix for strange cases (micros overflow)
if(Ts <= 0 || Ts > 0.5) Ts = 1e-3;
// current angle
float angle_c = getAngle();
// velocity calculation
float vel = (angle_c - angle_prev)/Ts;
// save variables for future pass
angle_prev = angle_c;
velocity_calc_timestamp = now_us;
return vel;
}
// set current angle as zero angle
// return the angle [rad] difference
float MagneticSensorI2C::initRelativeZero(){
float angle_offset = -getAngle();
zero_offset = natural_direction * getRawCount();
// angle tracking variables
full_rotation_offset = 0;
return angle_offset;
}
// set absolute zero angle as zero angle
// return the angle [rad] difference
float MagneticSensorI2C::initAbsoluteZero(){
float rotation = -(int)zero_offset;
// init absolute zero
zero_offset = 0;
// angle tracking variables
full_rotation_offset = 0;
// return offset in radians
return rotation / (float)cpr * _2PI;
}
// returns 0 if it has no absolute 0 measurement
// 0 - incremental encoder without index
// 1 - encoder with index & magnetic sensors
int MagneticSensorI2C::hasAbsoluteZero(){
return 1;
}
// returns 0 if it does need search for absolute zero
// 0 - magnetic sensor
// 1 - ecoder with index
int MagneticSensorI2C::needsAbsoluteZeroSearch(){
return 0;
}
// function reading the raw counter of the magnetic sensor
int MagneticSensorI2C::getRawCount(){
return (int)MagneticSensorI2C::read(angle_register_msb);
}
// I2C functions
/*
* Read a register from the sensor
* Takes the address of the register as a uint8_t
* Returns the value of the register
*/
int MagneticSensorI2C::read(uint8_t angle_reg_msb) {
// read the angle register first MSB then LSB
byte readArray[2];
uint16_t readValue = 0;
// notify the device that is aboout to be read
wire->beginTransmission(chip_address);
wire->write(angle_reg_msb);
wire->endTransmission(false);
// read the data msb and lsb
wire->requestFrom(chip_address, (uint8_t)2);
for (byte i=0; i < 2; i++) {
readArray[i] = wire->read();
}
// depending on the sensor architecture there are different combinations of
// LSB and MSB register used bits
// AS5600 uses 0..7 LSB and 8..11 MSB
// AS5048 uses 0..5 LSB and 6..13 MSB
readValue = ( readArray[1] & lsb_mask );
readValue += ( ( readArray[0] & msb_mask ) << lsb_used );
return readValue;
}
/*
* Checks whether other devices have locked the bus. Can clear SDA locks.
* This should be called before sensor.init() on devices that suffer i2c slaves locking sda
* e.g some stm32 boards with AS5600 chips
* Takes the sda_pin and scl_pin
* Returns 0 for OK, 1 for other master and 2 for unfixable sda locked LOW
*/
int MagneticSensorI2C::checkBus(byte sda_pin, byte scl_pin) {
pinMode(scl_pin, INPUT_PULLUP);
pinMode(sda_pin, INPUT_PULLUP);
delay(250);
if (digitalRead(scl_pin) == LOW) {
// Someone else has claimed master!");
return 1;
}
if(digitalRead(sda_pin) == LOW) {
// slave is communicating and awaiting clocks, we are blocked
pinMode(scl_pin, OUTPUT);
for (byte i = 0; i < 16; i++) {
// toggle clock for 2 bytes of data
digitalWrite(scl_pin, LOW);
delayMicroseconds(20);
digitalWrite(scl_pin, HIGH);
delayMicroseconds(20);
}
pinMode(sda_pin, INPUT);
delayMicroseconds(20);
if (digitalRead(sda_pin) == LOW) {
// SDA still blocked
return 2;
}
_delay(1000);
}
// SDA is clear (HIGH)
pinMode(sda_pin, INPUT);
pinMode(scl_pin, INPUT);
return 0;
}