How may I calibrate the LIS2MDL digital compass?

[ISanf.1]

I am working on creating a digital compass subsystem utilizing the LIS2MDL digital compass component. However, I am confused as to how its high & low offset registers function. The datasheet does not go into much detail in its description. I would humbly request for some clarification on their functions as I am trying to calibrate the digital compass so that it may show a perfect direction toward North at a level value for its y & z axes. I am trying to also adjust the compass so that its measured angle will remain the same, even should its angle in the y or z axes change somewhat.

For reference, I am attempting to control this digital compass with the ESP32 microcontroller.

I ask about these registers because I had found a code file online that was intended for all others to use freely. So while I did not write the code from scratch per say, I did change it from the original code by looking in the datasheet of the original component for which it was meant, saw what those registers were for & what each line of code did, and then changed the original code to be used for the LIS2MDL rather than the HMC5883L. The link to the original code may be seen below:

https://github.com/nkolban/esp32-snippets/blob/master/hardware/compass/hmc5883l.c

The changes to the code that I will be using may be seen below:

#include "driver/i2c.h"

#include "esp_log.h"

#include "freertos/FreeRTOS.h"

#include "freertos/task.h"

#include <math.h>

#include "sdkconfig.h"

#define PIN_SDA 14

#define PIN_CLK 16

#define I2C_ADDRESS 0b0011110

static char tag[] = "LIS2MDLTR";

#undef ESP_ERROR_CHECK

#define ESP_ERROR_CHECK(x) do { esp_err_t rc = (x); if (rc != ESP_OK) { ESP_LOGE("err", "esp_err_t = %d", rc); assert(0 && #x);} } while(0);

void app_main(void){

ESP_LOGD(tag, ">> LIS2MDLTR");

i2c_config_t conf;

conf.mode = I2C_MODE_MASTER;

conf.sda_io_num = PIN_SDA;

conf.scl_io_num = PIN_CLK;

conf.sda_pullup_en = GPIO_PULLUP_ENABLE;

conf.scl_pullup_en = GPIO_PULLUP_ENABLE;

conf.master.clk_speed = 100000;

ESP_ERROR_CHECK(i2c_param_config(I2C_NUM_0, &conf));

ESP_ERROR_CHECK(i2c_driver_install(I2C_NUM_0, I2C_MODE_MASTER, 0, 0, 0));

uint8_t data[6];

i2c_cmd_handle_t cmd = i2c_cmd_link_create();

i2c_master_start(cmd);

i2c_master_write_byte(cmd, (I2C_ADDRESS << 1) | I2C_MASTER_WRITE, 1);

i2c_master_write_byte(cmd, 0x60, 1); // Config A

i2c_master_write_byte(cmd, 0x80, 1); // Enable temp compensation and setup configuration register A according to datasheet guidelines

i2c_master_stop(cmd);

i2c_master_cmd_begin(I2C_NUM_0, cmd, 1000/portTICK_PERIOD_MS);

i2c_cmd_link_delete(cmd);

//maybe delete config B if not necessary

//Set value in "Configuration Register B"

cmd = i2c_cmd_link_create();

i2c_master_start(cmd);

i2c_master_write_byte(cmd, (I2C_ADDRESS << 1) | I2C_MASTER_WRITE, 1);

i2c_master_write_byte(cmd, 0x61, 1); // "Configuration Register B"

i2c_master_write_byte(cmd, 0x07, 1); // default setting check for later to know registers

i2c_master_stop(cmd);

i2c_master_cmd_begin(I2C_NUM_0, cmd, 1000/portTICK_PERIOD_MS);

i2c_cmd_link_delete(cmd);

//Set value in "Configuration Register C"

cmd = i2c_cmd_link_create();

i2c_master_start(cmd);

i2c_master_write_byte(cmd, (I2C_ADDRESS << 1) | I2C_MASTER_WRITE, 1);

i2c_master_write_byte(cmd, 0x62, 1); // "Configuration Register C"

i2c_master_write_byte(cmd, 0x01, 1); // Setup configuration register C according to datasheet guidelines

i2c_master_stop(cmd);

i2c_master_cmd_begin(I2C_NUM_0, cmd, 1000/portTICK_PERIOD_MS);

i2c_cmd_link_delete(cmd);

//Set active register to "Identification Register"

cmd = i2c_cmd_link_create();

ESP_ERROR_CHECK(i2c_master_start(cmd));

ESP_ERROR_CHECK(i2c_master_write_byte(cmd, (I2C_ADDRESS << 1) | I2C_MASTER_WRITE, 1));

ESP_ERROR_CHECK(i2c_master_write_byte(cmd, 0x4F, 1)); //"Identification Register"

ESP_ERROR_CHECK(i2c_master_stop(cmd));

ESP_ERROR_CHECK(i2c_master_cmd_begin(I2C_NUM_0, cmd, 100/portTICK_PERIOD_MS));

i2c_cmd_link_delete(cmd);

//Get data from Identification Register A, B and C

cmd = i2c_cmd_link_create();

ESP_ERROR_CHECK(i2c_master_start(cmd));

ESP_ERROR_CHECK(i2c_master_write_byte(cmd, (I2C_ADDRESS << 1) | I2C_MASTER_READ, 1));

i2c_master_read_byte(cmd, data,  0);

i2c_master_read_byte(cmd, data+1, 0);

i2c_master_read_byte(cmd, data+2, 1);

ESP_ERROR_CHECK(i2c_master_stop(cmd));

ESP_ERROR_CHECK(i2c_master_cmd_begin(I2C_NUM_0, cmd, 100/portTICK_PERIOD_MS));

i2c_cmd_link_delete(cmd);

while(1) {

//Set active register to "Data Output X MSB Register"

cmd = i2c_cmd_link_create();

i2c_master_start(cmd);

i2c_master_write_byte(cmd, (I2C_ADDRESS << 1) | I2C_MASTER_WRITE, 1);

i2c_master_write_byte(cmd, 0x69, 1); //0x69 = "Data Output X MSB Register"

i2c_master_stop(cmd);

i2c_master_cmd_begin(I2C_NUM_0, cmd, 1000/portTICK_PERIOD_MS);

i2c_cmd_link_delete(cmd);

//Read values for X, Y and Z

cmd = i2c_cmd_link_create();

i2c_master_start(cmd);

i2c_master_write_byte(cmd, (I2C_ADDRESS << 1) | I2C_MASTER_READ, 1);

i2c_master_read_byte(cmd, data,  0); //"Data Output X MSB Register"

i2c_master_read_byte(cmd, data+1, 0); //"Data Output X LSB Register"

i2c_master_read_byte(cmd, data+2, 0); //"Data Output Z MSB Register"

i2c_master_read_byte(cmd, data+3, 0); //"Data Output Z LSB Register"

i2c_master_read_byte(cmd, data+4, 0); //"Data Output Y MSB Register"

i2c_master_read_byte(cmd, data+5, 1); //"Data Output Y LSB Register "

i2c_master_stop(cmd);

i2c_master_cmd_begin(I2C_NUM_0, cmd, 1000/portTICK_PERIOD_MS);

i2c_cmd_link_delete(cmd);

short x = data[0] << 8 | data[1];

short z = data[2] << 8 | data[3];

short y = data[4] << 8 | data[5];

int angle = atan2((double)y,(double)x) * (180 / 3.14159265) + 180; // angle in degrees

ESP_LOGD(tag, "angle: %d, x: %d, y: %d, z: %d", angle, x, y, z);

printf("angle: %d, x: %d, y: %d, z: %d", angle, x, y, z);

vTaskDelay(1000/portTICK_PERIOD_MS);

}

vTaskDelete(NULL);

}

I would like to thank anyone who responds to this query in advance should they see it.

[Rstua.1]

I want to say that if you look at STMico's example code you will find that most if not all calculate offset and magnitude value in software. And then use those values to fix the raw values read from the chip - in software. I don't think I've see STMicro example code which writes to the chips offset registers.