Sensor hub no I2C communication using IIS2ILCX

[KoCT]

Hello,

I use the STEVAL-MKI209V1K with the IIS2ILCX sensor. I am trying to get the IIS2ILCX communicating with a second IIS2ILCX via sensor hub. The master sensor is connected to my MCU via SPI. Please find my „schematic“ and the configuration code below.

My problem is, that I cannot observe any I2C communication between the sensors. My oscilloscope just shows 3.4 V for each SCL and SDA. What could be wrong?

I would greatly appreciate any suggestions.

Additional information: i want to read the slaves data triggered by DRDY-Interrupt to get synchronized data of both sensors.

accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_FUNC_CFG_ACCESS, 0x00);
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_FIFO_CTRL1, 0x7F);
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_FIFO_CTRL2, 0x00);
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_FIFO_CTRL3, 0x07);
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_FIFO_CTRL4, 0x01);
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_INT1_CTRL, 0x00);
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_CTRL1_XL, 0x70);
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_CTRL3_C, 0x44); 
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_CTRL4_C, 0x04);
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_CTRL9_XL, 0x00);
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_MD1_CFG, 0x00);

// shub config
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_FUNC_CFG_ACCESS, 0x80);  // Activate access to shub registers
accelerometer_write_register(accel, ACCEL_IIS2ICLX_REG_ADDR_SLV0_ADD, 0x68);      // I2C address of sensor 2
accelerometer_write_register(accel, ACCEL_IIS2ICLX_REG_ADDR_SLV0_SUBADDR, ACCEL_IIS2ILCX_REG_ADDR_CTRL1_XL);  // set to 2 g and 833 Hz
accelerometer_write_register(accel, ACCEL_IIS2ICLX_REG_ADDR_DATAWRITE_SLV0, 0x7C);// power-down, 2 g
accelerometer_write_register(accel, ACCEL_IIS2ICLX_REG_ADDR_SLV0_ADD, 0x68);      // I2C address of sensor 2
accelerometer_write_register(accel, ACCEL_IIS2ICLX_REG_ADDR_SLV0_SUBADDR, ACCEL_IIS2ILCX_REG_ADDR_INT2_CTRL);  // set to 2 g and 833 Hz
accelerometer_write_register(accel, ACCEL_IIS2ICLX_REG_ADDR_DATAWRITE_SLV0, 0x01);// power-down, 2 g
accelerometer_write_register(accel, ACCEL_IIS2ICLX_REG_ADDR_SLV0_ADD, 0x68);      // I2C address of sensor 2
accelerometer_write_register(accel, ACCEL_IIS2ICLX_REG_ADDR_SLV0_SUBADDR, 0x28);  // OUTX_L_A register //! could be changed to 0x2A for Y-axis
accelerometer_write_register(accel, ACCEL_IIS2ICLX_REG_ADDR_SLV0_CONFIG, 0x0A);   // SHUB-ODR = 0 Hz, FIFO data batching enabled, 2 read operations
accelerometer_write_register(accel, ACCEL_IIS2ICLX_REG_ADDR_SHUB_MASTER_CONFIG, 0x24); // MASTER_ON, 1 ext sensor, START CONFIG
accelerometer_write_register(accel, ACCEL_IIS2ILCX_REG_ADDR_FUNC_CFG_ACCESS, 0x00);  // deactivate shub register access

[TDK]

Do any slave addresses respond to HAL_I2C_IsDeviceReady? Note that HAL expects the 7-bit address to be left-shifted by 1 bit.

[KoCT]

The communication with the "master" sensor via SPI works fine. I am using an ESP32. Therefore I provide my write function here:

static bool accelerometer_write_register(accel_iis2ilcx_t *accel, uint8_t address, uint8_t reg_value) 
{
	unsigned char write_buf[2];
	write_buf[0] = address & ~(1 << 7);
	write_buf[1] = reg_value;

	return spi_interface_write(accel->spi_device, write_buf, 2);
}

I guess that the sensor hub i2c is not directly accessible for me, right?