Electronic – STM32F4 I2C read out with least overhead

I have a sensor connected over I2C, where I read out data at a constant address. The uC is an STM32F410CB with 100MHz. A control loop runs at around 16kHz without reading out the sensor and drops to 5 kHz when I always read out the sensor. I2C is configured in the fast mode (400kHz).

So I decided to use the DMA, where a function is available in the HAL libraries that look pretty promising:

HAL_I2C_Mem_Read_DMA(i2c1,addr,addr_mem,addr_mem_size,data,data_size);

So I implemented this function, which is also called every cycle the control loop runs. The frequency of the control loop increased to 7kHz now, but that's still not enough for my application. Only 3 Interrupts are generated for the read out, I don't know where this huge overhead comes from. When I only call the function every third time, the control loop runs twice at 16kHz, then once at 7kHz. I need a more stable result. Is there a way to fully autonomous read out a sensor over I2C at a constant register address, such that nearly no overhead is generated?

/**
  * @brief  Reads an amount of data in non-blocking mode with DMA from a specific memory address.
  * @param  hi2c Pointer to a I2C_HandleTypeDef structure that contains
  *                the configuration information for the specified I2C.
  * @param  DevAddress Target device address
  * @param  MemAddress Internal memory address
  * @param  MemAddSize Size of internal memory address
  * @param  pData Pointer to data buffer
  * @param  Size Amount of data to be read
  * @retval HAL status
  */
HAL_StatusTypeDef HAL_I2C_Mem_Read_DMA(I2C_HandleTypeDef *hi2c, uint16_t DevAddress, uint16_t MemAddress, uint16_t MemAddSize, uint8_t *pData, uint16_t Size)
{
  uint32_t tickstart = 0x00U;
  __IO uint32_t count = 0U;

  /* Init tickstart for timeout management*/
  tickstart = HAL_GetTick();

  /* Check the parameters */
  assert_param(IS_I2C_MEMADD_SIZE(MemAddSize));

  if(hi2c->State == HAL_I2C_STATE_READY)
  {
    /* Wait until BUSY flag is reset */
    count = I2C_TIMEOUT_BUSY_FLAG * (SystemCoreClock /25U /1000U);
    do
    {
      if(count-- == 0U)
      {
        hi2c->PreviousState = I2C_STATE_NONE;
        hi2c->State= HAL_I2C_STATE_READY;

        /* Process Unlocked */
        __HAL_UNLOCK(hi2c);

        return HAL_TIMEOUT; 
      }
    }
    while(__HAL_I2C_GET_FLAG(hi2c, I2C_FLAG_BUSY) != RESET);

    /* Process Locked */
    __HAL_LOCK(hi2c);

    /* Check if the I2C is already enabled */
    if((hi2c->Instance->CR1 & I2C_CR1_PE) != I2C_CR1_PE)
    {
      /* Enable I2C peripheral */
      __HAL_I2C_ENABLE(hi2c);
    }

    /* Disable Pos */
    hi2c->Instance->CR1 &= ~I2C_CR1_POS;

    hi2c->State     = HAL_I2C_STATE_BUSY_RX;
    hi2c->Mode      = HAL_I2C_MODE_MEM;
    hi2c->ErrorCode = HAL_I2C_ERROR_NONE;

    /* Prepare transfer parameters */
    hi2c->pBuffPtr = pData;
    hi2c->XferCount = Size;
    hi2c->XferOptions = I2C_NO_OPTION_FRAME;
    hi2c->XferSize    = hi2c->XferCount;

    if(hi2c->XferSize > 0U)
    {
      /* Set the I2C DMA transfer complete callback */
      hi2c->hdmarx->XferCpltCallback = I2C_DMAXferCplt;

      /* Set the DMA error callback */
      hi2c->hdmarx->XferErrorCallback = I2C_DMAError;

      /* Set the unused DMA callbacks to NULL */
      hi2c->hdmarx->XferHalfCpltCallback = NULL;
      hi2c->hdmarx->XferM1CpltCallback = NULL;
      hi2c->hdmarx->XferM1HalfCpltCallback = NULL;
      hi2c->hdmarx->XferAbortCallback = NULL;

      /* Enable the DMA Stream */
      HAL_DMA_Start_IT(hi2c->hdmarx, (uint32_t)&hi2c->Instance->DR, (uint32_t)hi2c->pBuffPtr, hi2c->XferSize);

      /* Send Slave Address and Memory Address */
      if(I2C_RequestMemoryRead(hi2c, DevAddress, MemAddress, MemAddSize, I2C_TIMEOUT_FLAG, tickstart) != HAL_OK)
      {
        if(hi2c->ErrorCode == HAL_I2C_ERROR_AF)
        {
          /* Process Unlocked */
          __HAL_UNLOCK(hi2c);
          return HAL_ERROR;
        }
        else
        {
          /* Process Unlocked */
          __HAL_UNLOCK(hi2c);
          return HAL_TIMEOUT;
        }
      }

      if(Size == 1U)
      {
        /* Disable Acknowledge */
        hi2c->Instance->CR1 &= ~I2C_CR1_ACK;
      }
      else
      {
        /* Enable Last DMA bit */
        hi2c->Instance->CR2 |= I2C_CR2_LAST;
      }

      /* Clear ADDR flag */
      __HAL_I2C_CLEAR_ADDRFLAG(hi2c);

      /* Process Unlocked */
      __HAL_UNLOCK(hi2c);

      /* Note : The I2C interrupts must be enabled after unlocking current process
                to avoid the risk of I2C interrupt handle execution before current
                process unlock */
      /* Enable ERR interrupt */
      __HAL_I2C_ENABLE_IT(hi2c, I2C_IT_ERR);

     /* Enable DMA Request */
      hi2c->Instance->CR2 |= I2C_CR2_DMAEN;
    }
    else
    {
      /* Send Slave Address and Memory Address */
      if(I2C_RequestMemoryRead(hi2c, DevAddress, MemAddress, MemAddSize, I2C_TIMEOUT_FLAG, tickstart) != HAL_OK)
      {
        if(hi2c->ErrorCode == HAL_I2C_ERROR_AF)
        {
          /* Process Unlocked */
          __HAL_UNLOCK(hi2c);
          return HAL_ERROR;
        }
        else
        {
          /* Process Unlocked */
          __HAL_UNLOCK(hi2c);
          return HAL_TIMEOUT;
        }
      }

      /* Clear ADDR flag */
      __HAL_I2C_CLEAR_ADDRFLAG(hi2c);

      /* Generate Stop */
      hi2c->Instance->CR1 |= I2C_CR1_STOP;

      hi2c->State = HAL_I2C_STATE_READY;

      /* Process Unlocked */
      __HAL_UNLOCK(hi2c);
    }

    return HAL_OK;
  }
  else
  {
    return HAL_BUSY;
  }
}

Edit: Here is the code for the I2C readout:

Low Level:

//DMA I2C
err_t I2C_Driver_TXRX_DMA(uint16_t addr, uint16_t addr_mem, uint8_t* pData, uint16_t size) {
    addr = addr << 1;
    err_t err={.value=HAL_OK};

    err.value=HAL_I2C_Mem_Read_DMA(i2c1,addr,addr_mem,1,pData,size); //Error callback called in error case

    return err;
}

Higher Layer:

uint8_t buf_rx[2]={0};
uint16_t pos=0;

void triggerDMAMeasurementPosition() {
    if(getI2CErrorState()) {
        I2C_Error_Solver(ENC_ADDR);
        i2c_err=0;
    } else {
        I2C_Driver_TXRX_DMA(ENC_ADDR,RAW_ANGLE_ADDR,buf_rx,2);
    }
}

void HAL_I2C_MemRxCpltCallback(I2C_HandleTypeDef *hi2c) {
    pos=buf_rx[0]<<8 | buf_rx[1];
}

I2C Init:

/* I2C1 init function */
static void MX_I2C1_Init(void)
{

  hi2c1.Instance = I2C1;
  hi2c1.Init.ClockSpeed = 400000;
  hi2c1.Init.DutyCycle = I2C_DUTYCYCLE_2;
  hi2c1.Init.OwnAddress1 = 0;
  hi2c1.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
  hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
  hi2c1.Init.OwnAddress2 = 0;
  hi2c1.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
  hi2c1.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
  if (HAL_I2C_Init(&hi2c1) != HAL_OK)
  {
    _Error_Handler(__FILE__, __LINE__);
  }

}

Edit 2: BTW, the slow down happens only when HAL_DMA_Start_IT(..) is called inside HAL_I2C_Mem_Read_DMA(..). So it is probably somehow related to the interrupts and what happens inside there.