MPU9250 with STM32 - Magnetometer readings are constant - stm32

Question

Trying to use MPU9250 IMU sensor with my STM32G431RB NUCLEO board. The IMU's accelerometer and gyroscope are working fine. However, magnetometer gives constant values.
I think magnetometers power mode is set to read-once or off. However, I did not understand what the problem was.
On GitHub, I tried to implement the MPU9250 library that kriswiner wrote for Arduino. But I don't know whether I succeeded or failed.
The original code I implemented:
https://github.com/kriswiner/MPU9250/blob/master/MPU9250BasicAHRS.ino
The CubeIDE code I wrote for STM32, to configure and read magnetometer:
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "i2c.h"
#include "usart.h"
#include "gpio.h"
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include <stdio.h>
#include <math.h>
/* USER CODE END Includes */
/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */
/* USER CODE END PTD */
/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
//Magnetometer Registers
#define AK8963_ADDRESS 0x0C<<1
#define AK8963_WHO_AM_I 0x00 // should return 0x48
#define AK8963_INFO 0x01
#define AK8963_ST1 0x02 // data ready status bit 0
#define AK8963_XOUT_L 0x03 // data
#define AK8963_XOUT_H 0x04
#define AK8963_YOUT_L 0x05
#define AK8963_YOUT_H 0x06
#define AK8963_ZOUT_L 0x07
#define AK8963_ZOUT_H 0x08
#define AK8963_ST2 0x09 // Data overflow bit 3 and data read error status bit 2
#define AK8963_CNTL 0x0A // Power down (0000), single-measurement (0001), self-test (1000) and Fuse ROM (1111) modes on bits 3:0
#define AK8963_ASTC 0x0C // Self test control
#define AK8963_I2CDIS 0x0F // I2C disable
#define AK8963_ASAX 0x10 // Fuse ROM x-axis sensitivity adjustment value
#define AK8963_ASAY 0x11 // Fuse ROM y-axis sensitivity adjustment value
#define AK8963_ASAZ 0x12 // Fuse ROM z-axis sensitivity adjustment value
#define WHO_AM_I_MPU9250 0x75 // Should return 0x71
#define MPU9250_ADDRESS 0x68<<1
#define INT_PIN_CFG 0x37
/* USER CODE END PD */
/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
/* USER CODE END PM */
/* Private variables ---------------------------------------------------------*/
/* USER CODE BEGIN PV */
enum Mscale {
MFS_14BITS = 0, // 0.6 mG per LSB
MFS_16BITS // 0.15 mG per LSB
};
uint8_t Mscale = MFS_16BITS; // Choose either 14-bit or 16-bit magnetometer resolution
uint8_t Mmode = 0x02;
const uint16_t i2c_timeoutB = 100;
/* USER CODE END PV */
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
/* USER CODE BEGIN PFP */
/* USER CODE END PFP */
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
int _write(int file, char *ptr, int len)
{
HAL_UART_Transmit(&hlpuart1, (uint8_t*)ptr, len, HAL_MAX_DELAY);
return len;
}
float MagnetoX;
float MagnetoY;
float MagnetoZ;
/* USER CODE END 0 */
/**
* #brief The application entry point.
* #retval int
*/
int main(void)
{
/* USER CODE BEGIN 1 */
/* USER CODE END 1 */
/* MCU Configuration--------------------------------------------------------*/
/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
HAL_Init();
/* USER CODE BEGIN Init */
/* USER CODE END Init */
/* Configure the system clock */
SystemClock_Config();
/* USER CODE BEGIN SysInit */
/* USER CODE END SysInit */
/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_LPUART1_UART_Init();
MX_I2C3_Init();
MX_I2C2_Init();
/* USER CODE BEGIN 2 */
printf("**************************** \r\n");
printf("MPU9250 STM32 Implementation \r\n");
printf("**************************** \r\n");
//pre-def. vars
uint8_t readData;
uint8_t writeData;
// Check MPU and Mag---------------------------------------------------------------------------------------------------
//read MPU9255 WHOAMI
HAL_I2C_Mem_Read(&hi2c2, MPU9250_ADDRESS, WHO_AM_I_MPU9250, 1, &readData, 1, i2c_timeoutB);
printf("MPU WHO AM I is (Must return 113): %d\r\n", readData);
//enable Mag bypass
writeData = 0x22;
HAL_I2C_Mem_Write(&hi2c2, MPU9250_ADDRESS, INT_PIN_CFG, 1, &writeData, 1, i2c_timeoutB);
//read AK8963 WHOAMI
HAL_I2C_Mem_Read(&hi2c2, AK8963_ADDRESS, AK8963_WHO_AM_I, 1, &readData, 1, i2c_timeoutB);
printf("MAG WHO AM I is (Must return 72): %d\r\n", readData);
printf("------------------------------------------------\r\n");
//Init Mag-------------------------------------------------------------------------------------------------------------
//Power down magnetometer
writeData = 0x00;
HAL_I2C_Mem_Write(&hi2c2, AK8963_ADDRESS, AK8963_CNTL, 1, &writeData, 1, i2c_timeoutB);
HAL_Delay(100);
//Enter Fuse ROM access mode
writeData = 0x0F;
HAL_I2C_Mem_Write(&hi2c2, AK8963_ADDRESS, AK8963_CNTL, 1, &writeData, 1, i2c_timeoutB);
HAL_Delay(100);
//Read the x-, y-, and z-axis calibration values
uint8_t rawMagCalData[3];
HAL_I2C_Mem_Read(&hi2c2, AK8963_ADDRESS, AK8963_ASAX, 1, &rawMagCalData[0], 3, i2c_timeoutB);
float calMagX = (float)(rawMagCalData[0] - 128)/256. + 1.; // Return x-axis sensitivity adjustment values, etc.
float calMagY = (float)(rawMagCalData[1] - 128)/256. + 1.;
float calMagZ = (float)(rawMagCalData[2] - 128)/256. + 1.;
printf("Mag cal off X: %f\r\n", calMagX);
printf("Mag cal off Y: %f\r\n", calMagY);
printf("Mag cal off Z: %f\r\n", calMagZ);
HAL_Delay(100);
//Set magnetometer data resolution and sample ODR
writeData = Mscale << 4 | Mmode;
printf("writeData: %d\r\n", writeData);
HAL_I2C_Mem_Write(&hi2c2, AK8963_ADDRESS, AK8963_CNTL, 1, &writeData, 1, i2c_timeoutB);
HAL_Delay(100);
printf("------------------------------------------------\r\n");
//Read Mag-------------------------------------------------------------------------------------------------------------
//Read Mag data
uint8_t rawMagData[6];
HAL_I2C_Mem_Read(&hi2c2, AK8963_ADDRESS, AK8963_XOUT_L, 1, &rawMagData[0], 6, i2c_timeoutB);
float MagX = ((int16_t)rawMagData[1] << 8) | rawMagData[0];
float MagY = ((int16_t)rawMagData[3] << 8) | rawMagData[2];
float MagZ = ((int16_t)rawMagData[5] << 8) | rawMagData[4];
printf("Mag X: %f\r\n", MagX);
printf("Mag Y: %f\r\n", MagY);
printf("Mag Z: %f\r\n", MagZ);
HAL_Delay(100);
printf("------------------------------------------------\r\n");
/* USER CODE END 2 */
/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
/* USER CODE END WHILE */
//Read Mag data
uint8_t rawMagData[6];
HAL_I2C_Mem_Read(&hi2c2, AK8963_ADDRESS, AK8963_XOUT_L, 1, &rawMagData[0], 6, i2c_timeoutB);
MagX = ((int16_t)rawMagData[1] << 8) | rawMagData[0];
MagY = ((int16_t)rawMagData[3] << 8) | rawMagData[2];
MagZ = ((int16_t)rawMagData[5] << 8) | rawMagData[4];
//Print to Com port via STLINK
printf("Mag X: %f\r\n", MagX);
printf("Mag Y: %f\r\n", MagY);
printf("Mag Z: %f\r\n", MagZ);
printf("------------------------------------------------\r\n");
HAL_Delay(1000);
/* USER CODE BEGIN 3 */
}
/* USER CODE END 3 */
}
UART tab for readings:
MPU9250 and Mag.'s WHOAMI readings are fine.

Answer 1

When I studied the code a little more, I found that I made some critical mistakes.
After I post this question, I saw an article about reading data from MPU9250.
https://longnight975551865.wordpress.com/2018/02/11/how-to-read-data-from-mpu9250/
Although it is an article written for Arduino, it explained very well how register operations should be done in MPU9250 and especially how power management should be done. I saw that I had configured the AK8963 (magnetometer) incorrectly, and I realized that I was trying to read the data from the AK8963 incorrectly.
I will explain step by step my mistakes and solutions.
1)
After FUSE ROM access, I should have reset AK8963 but I continued without resetting.
Before writing the data resolution and sample ODR values, we need to reset the power mode by typing 0x00 into the AK8963_CNTL register.
//Power down magnetometer
writeData = 0x00;
HAL_I2C_Mem_Write(&hi2c2, AK8963_ADDRESS, AK8963_CNTL, 1, &writeData, 1, i2c_timeoutB);
HAL_Delay(100);
Also, in the code that I shared, I was trying to read data as soon as I init the magnetometer, but this was also an inaccurate method because the way of reading the data is different compared to the accelerometer or gyroscope. That's why I deleted this part as well.
3)
The magnetometer's data reading process must be accurate. At first, it is necessary to read the register AK8963_ST1 and enable data updating.
HAL_I2C_Mem_Read(&hi2c2, AK8963_ADDRESS, AK8963_ST1, 1, &readData, 1, i2c_timeoutB);
printf("Read Data: %d\r\n", readData);
printf("Read Data2: %d\r\n", (readData & 0x01));
if( (readData & 0x01) == 0x01 ){
//Read Mag data
uint8_t rawMagData[7];
HAL_I2C_Mem_Read(&hi2c2, AK8963_ADDRESS, AK8963_XOUT_L, 1, &rawMagData[0], 7, i2c_timeoutB);
uint8_t c = rawMagData[6];
if(!(c & 0x08)) {
MagX = ((int16_t)rawMagData[1] << 8) | rawMagData[0];
MagY = ((int16_t)rawMagData[3] << 8) | rawMagData[2];
MagZ = ((int16_t)rawMagData[5] << 8) | rawMagData[4];
//Print to Com port via STLINK
printf("Mag X: %f\r\n", MagX);
printf("Mag Y: %f\r\n", MagY);
printf("Mag Z: %f\r\n", MagZ);
printf("------------------------------------------------\r\n");
}
}
else {
printf("No Data? \r\n");
printf("------------------------------------------------\r\n");
}
HAL_Delay(500);
New, updated code:
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "i2c.h"
#include "usart.h"
#include "gpio.h"
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include <stdio.h>
#include <math.h>
/* USER CODE END Includes */
/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */
/* USER CODE END PTD */
/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
//Magnetometer Registers
#define AK8963_ADDRESS 0x0C<<1
#define AK8963_WHO_AM_I 0x00 // should return 0x48
#define AK8963_INFO 0x01
#define AK8963_ST1 0x02 // data ready status bit 0
#define AK8963_XOUT_L 0x03 // data
#define AK8963_XOUT_H 0x04
#define AK8963_YOUT_L 0x05
#define AK8963_YOUT_H 0x06
#define AK8963_ZOUT_L 0x07
#define AK8963_ZOUT_H 0x08
#define AK8963_ST2 0x09 // Data overflow bit 3 and data read error status bit 2
#define AK8963_CNTL 0x0A // Power down (0000), single-measurement (0001), self-test (1000) and Fuse ROM (1111) modes on bits 3:0
#define AK8963_ASTC 0x0C // Self test control
#define AK8963_I2CDIS 0x0F // I2C disable
#define AK8963_ASAX 0x10 // Fuse ROM x-axis sensitivity adjustment value
#define AK8963_ASAY 0x11 // Fuse ROM y-axis sensitivity adjustment value
#define AK8963_ASAZ 0x12 // Fuse ROM z-axis sensitivity adjustment value
#define WHO_AM_I_MPU9250 0x75 // Should return 0x71
#define MPU9250_ADDRESS 0x68<<1
#define INT_PIN_CFG 0x37
#define DATA_READY_MASK 0x01
#define MAGIC_OVERFLOW_MASK 0x8
/* USER CODE END PD */
/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
/* USER CODE END PM */
/* Private variables ---------------------------------------------------------*/
float MagX;
float MagY;
float MagZ;
/* USER CODE BEGIN PV */
enum Mscale {
MFS_14BITS = 0, // 0.6 mG per LSB
MFS_16BITS // 0.15 mG per LSB
};
uint8_t Mscale = MFS_16BITS; // Choose either 14-bit or 16-bit magnetometer resolution
uint8_t Mmode = 0x02;
const uint16_t i2c_timeoutB = 100;
/* USER CODE END PV */
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
/* USER CODE BEGIN PFP */
/* USER CODE END PFP */
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
int _write(int file, char *ptr, int len)
{
HAL_UART_Transmit(&hlpuart1, (uint8_t*)ptr, len, HAL_MAX_DELAY);
return len;
}
float MagnetoX;
float MagnetoY;
float MagnetoZ;
/* USER CODE END 0 */
/**
* #brief The application entry point.
* #retval int
*/
int main(void)
{
/* USER CODE BEGIN 1 */
/* USER CODE END 1 */
/* MCU Configuration--------------------------------------------------------*/
/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
HAL_Init();
/* USER CODE BEGIN Init */
/* USER CODE END Init */
/* Configure the system clock */
SystemClock_Config();
/* USER CODE BEGIN SysInit */
/* USER CODE END SysInit */
/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_LPUART1_UART_Init();
MX_I2C3_Init();
MX_I2C2_Init();
/* USER CODE BEGIN 2 */
printf("**************************** \r\n");
printf("MPU9250 STM32 Implementation \r\n");
printf("**************************** \r\n");
//pre-def. vars
uint8_t readData;
uint8_t writeData;
// Check MPU and Mag---------------------------------------------------------------------------------------------------
//read MPU9255 WHOAMI
HAL_I2C_Mem_Read(&hi2c2, MPU9250_ADDRESS, WHO_AM_I_MPU9250, 1, &readData, 1, i2c_timeoutB);
printf("MPU WHO AM I is (Must return 113): %d\r\n", readData);
//enable Mag bypass
writeData = 0x22;
HAL_I2C_Mem_Write(&hi2c2, MPU9250_ADDRESS, INT_PIN_CFG, 1, &writeData, 1, i2c_timeoutB);
//read AK8963 WHOAMI
HAL_I2C_Mem_Read(&hi2c2, AK8963_ADDRESS, AK8963_WHO_AM_I, 1, &readData, 1, i2c_timeoutB);
printf("MAG WHO AM I is (Must return 72): %d\r\n", readData);
printf("------------------------------------------------\r\n");
//Init Mag-------------------------------------------------------------------------------------------------------------
//Power down magnetometer
writeData = 0x00;
HAL_I2C_Mem_Write(&hi2c2, AK8963_ADDRESS, AK8963_CNTL, 1, &writeData, 1, i2c_timeoutB);
HAL_Delay(100);
//Enter Fuse ROM access mode
writeData = 0x0F;
HAL_I2C_Mem_Write(&hi2c2, AK8963_ADDRESS, AK8963_CNTL, 1, &writeData, 1, i2c_timeoutB);
HAL_Delay(100);
//Read the x-, y-, and z-axis calibration values
uint8_t rawMagCalData[3];
HAL_I2C_Mem_Read(&hi2c2, AK8963_ADDRESS, AK8963_ASAX, 1, &rawMagCalData[0], 3, i2c_timeoutB);
float calMagX = (float)(rawMagCalData[0] - 128)/256. + 1.; // Return x-axis sensitivity adjustment values, etc.
float calMagY = (float)(rawMagCalData[1] - 128)/256. + 1.;
float calMagZ = (float)(rawMagCalData[2] - 128)/256. + 1.;
printf("Mag cal off X: %f\r\n", calMagX);
printf("Mag cal off Y: %f\r\n", calMagY);
printf("Mag cal off Z: %f\r\n", calMagZ);
HAL_Delay(100);
//Power down magnetometer
writeData = 0x00;
HAL_I2C_Mem_Write(&hi2c2, AK8963_ADDRESS, AK8963_CNTL, 1, &writeData, 1, i2c_timeoutB);
HAL_Delay(100);
//Set magnetometer data resolution and sample ODR
writeData = Mscale << 4 | 0x02;
//writeData = 0x16;
printf("writeData: %d\r\n", writeData);
HAL_I2C_Mem_Write(&hi2c2, AK8963_ADDRESS, AK8963_CNTL, 1, &writeData, 1, i2c_timeoutB);
HAL_Delay(100);
printf("------------------------------------------------\r\n");
/*
//Read Mag-------------------------------------------------------------------------------------------------------------
//Read Mag data
uint8_t rawMagData[6];
HAL_I2C_Mem_Read(&hi2c2, AK8963_ADDRESS, AK8963_XOUT_L, 1, &rawMagData[0], 6, i2c_timeoutB);
MagX = ((int16_t)rawMagData[1] << 8) | rawMagData[0];
MagY = ((int16_t)rawMagData[3] << 8) | rawMagData[2];
MagZ = ((int16_t)rawMagData[5] << 8) | rawMagData[4];
printf("Mag X: %f\r\n", MagX);
printf("Mag Y: %f\r\n", MagY);
printf("Mag Z: %f\r\n", MagZ);
HAL_Delay(100);
printf("------------------------------------------------\r\n");
*/
/* USER CODE END 2 */
/* Infinite loop */
/* USER CODE BEGIN WHILE */
while (1)
{
/* USER CODE END WHILE */
HAL_I2C_Mem_Read(&hi2c2, AK8963_ADDRESS, AK8963_ST1, 1, &readData, 1, i2c_timeoutB);
printf("Read Data: %d\r\n", readData);
printf("Read Data2: %d\r\n", (readData & 0x01));
if( (readData & 0x01) == 0x01 ){
//Read Mag data
uint8_t rawMagData[7];
HAL_I2C_Mem_Read(&hi2c2, AK8963_ADDRESS, AK8963_XOUT_L, 1, &rawMagData[0], 7, i2c_timeoutB);
uint8_t c = rawMagData[6];
if(!(c & 0x08)) {
MagX = ((int16_t)rawMagData[1] << 8) | rawMagData[0];
MagY = ((int16_t)rawMagData[3] << 8) | rawMagData[2];
MagZ = ((int16_t)rawMagData[5] << 8) | rawMagData[4];
//Print to Com port via STLINK
printf("Mag X: %f\r\n", MagX);
printf("Mag Y: %f\r\n", MagY);
printf("Mag Z: %f\r\n", MagZ);
printf("------------------------------------------------\r\n");
}
}
else {
printf("No Data? \r\n");
printf("------------------------------------------------\r\n");
}
HAL_Delay(500);
/* USER CODE BEGIN 3 */
}
/* USER CODE END 3 */
}
It's a simple mistake because I didn't read the datasheet truly. I hope it will be a good resource for people experiencing the same error. :)

Answer 2

Read ST2 register from the magnetometer to enable data updating after each reading of the measurement registers.
From the datasheet:
When any of measurement data register (HXL ~ HZH) or ST2 register is
read, AK8963 judges that data reading is started.
...
When ST2 register is read, AK8963 judges that data reading is
finished. Stored measurement data is protected during data reading and
data is not updated.
To avoid receiving incomplete or duplicate data you should implement the correct reading sequence as specified in the above datasheet, part 6.4.3.2. Normal Read Sequence