STM32L475VG DAC configuration issue: no signal observable on GPIO?

[BHM]

I'm trying to get a very simple example working with the DAC on the STM32L475VG in the B-L475E-IOT01A development board. I've generated the code below with STM32CubeMX for use in STM32CubeIDE. I can see the DAC register values changing, and LD1 blinks, but can't pick up a signal on any of the output pins A3-A5 (for the OPAMP amplified signal, or either DAC channels).

I imagine I've overlooked some configuration detail, but I can't figure out what! Any insight would be greatly appreciated.

Cheers,

Brett

/* Includes ------------------------------------------------------------------*/
#include "main.h"
 
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
 
/* USER CODE END Includes */
 
/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */
 
/* USER CODE END PTD */
 
/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
/* USER CODE END PD */
 
/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
 
/* USER CODE END PM */
 
/* Private variables ---------------------------------------------------------*/
DAC_HandleTypeDef hdac1;
 
OPAMP_HandleTypeDef hopamp1;
 
/* USER CODE BEGIN PV */
 
/* USER CODE END PV */
 
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_DAC1_Init(void);
static void MX_OPAMP1_Init(void);
/* USER CODE BEGIN PFP */
 
/* USER CODE END PFP */
 
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
 
/* 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_DAC1_Init();
  MX_OPAMP1_Init();
  /* USER CODE BEGIN 2 */
 
  /* USER CODE END 2 */
 
  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  // initialize variables for the DACs
  uint8_t triangle=0, rising=1, saw=0;
  uint32_t data=0;
  #define TRI_CHANNEL DAC_CHANNEL_1
  #define SAW_CHANNEL DAC_CHANNEL_2 // we can observe the saw wave on LED1
 
  // start the DACs
  HAL_DAC_Start(&hdac1, DAC_CHANNEL_1);
  HAL_DAC_Start(&hdac1, DAC_CHANNEL_2);
 
  while (1)
  {
    /* USER CODE END WHILE */
 
    /* USER CODE BEGIN 3 */
	  // PART 1
	  if (HAL_GPIO_ReadPin(B2_GPIO_Port, B2_Pin)) {
		  // if the pin value is true, then the button IS NOT pressed (pull-up by default)
		  HAL_GPIO_WritePin(LED_GPIO_Port, LED_Pin, GPIO_PIN_RESET);
	  } else {
		  // if the pin value is false, then the button IS pressed (button connects to GND)
		  HAL_GPIO_WritePin(LED_GPIO_Port, LED_Pin, GPIO_PIN_SET);
	  } // if-else
 
	  // PART 2
	  // check if it's time for the triangle wave to decrease
	  if (triangle == UINT8_MAX+1 - 32)
		  rising = 0;
 
	  if (triangle == 0)
		  rising = 1;
 
	  // C2 freqeuency is 65 Hz, or with a period of 15 ms. We could
	  // divide into 16 steps as an approximation.
 
	  // update triangle and saw values
 
	  // triangle rises and falls, and must complete the cycle in 16 steps
	  if (rising)
		  triangle += 32;
	  else
		  triangle -= 32;
 
	  // saw rises and then overflows; a cycle must be completed in 16 steps
	  saw += 16;
 
	  // write a value for the triangle wave
	  HAL_DAC_SetValue(&hdac1, TRI_CHANNEL, DAC_ALIGN_8B_R, triangle);
	  data = HAL_DAC_GetValue(&hdac1, TRI_CHANNEL);
	  HAL_DAC_SetValue(&hdac1, SAW_CHANNEL, DAC_ALIGN_8B_R, saw);
	  data = HAL_DAC_GetValue(&hdac1, SAW_CHANNEL);
 
	  // wait for 1 ms
	  HAL_Delay(1);
  }
  /* USER CODE END 3 */
}
 
/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
 
  /** Initializes the CPU, AHB and APB busses clocks 
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_MSI;
  RCC_OscInitStruct.MSIState = RCC_MSI_ON;
  RCC_OscInitStruct.MSICalibrationValue = 0;
  RCC_OscInitStruct.MSIClockRange = RCC_MSIRANGE_6;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_MSI;
  RCC_OscInitStruct.PLL.PLLM = 1;
  RCC_OscInitStruct.PLL.PLLN = 40;
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV7;
  RCC_OscInitStruct.PLL.PLLQ = RCC_PLLQ_DIV2;
  RCC_OscInitStruct.PLL.PLLR = RCC_PLLR_DIV2;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }
  /** Initializes the CPU, AHB and APB busses clocks 
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
 
  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)
  {
    Error_Handler();
  }
  /** Configure the main internal regulator output voltage 
  */
  if (HAL_PWREx_ControlVoltageScaling(PWR_REGULATOR_VOLTAGE_SCALE1) != HAL_OK)
  {
    Error_Handler();
  }
}
 
/**
  * @brief DAC1 Initialization Function
  * @param None
  * @retval None
  */
static void MX_DAC1_Init(void)
{
 
  /* USER CODE BEGIN DAC1_Init 0 */
 
  /* USER CODE END DAC1_Init 0 */
 
  DAC_ChannelConfTypeDef sConfig = {0};
 
  /* USER CODE BEGIN DAC1_Init 1 */
 
  /* USER CODE END DAC1_Init 1 */
  /** DAC Initialization 
  */
  hdac1.Instance = DAC1;
  if (HAL_DAC_Init(&hdac1) != HAL_OK)
  {
    Error_Handler();
  }
  /** DAC channel OUT1 config 
  */
  sConfig.DAC_SampleAndHold = DAC_SAMPLEANDHOLD_DISABLE;
  sConfig.DAC_Trigger = DAC_TRIGGER_NONE;
  sConfig.DAC_OutputBuffer = DAC_OUTPUTBUFFER_ENABLE;
  sConfig.DAC_ConnectOnChipPeripheral = DAC_CHIPCONNECT_ENABLE;
  sConfig.DAC_UserTrimming = DAC_TRIMMING_FACTORY;
  if (HAL_DAC_ConfigChannel(&hdac1, &sConfig, DAC_CHANNEL_1) != HAL_OK)
  {
    Error_Handler();
  }
  /** DAC channel OUT2 config 
  */
  sConfig.DAC_ConnectOnChipPeripheral = DAC_CHIPCONNECT_ENABLE;
  if (HAL_DAC_ConfigChannel(&hdac1, &sConfig, DAC_CHANNEL_2) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN DAC1_Init 2 */
 
  /* USER CODE END DAC1_Init 2 */
 
}
 
/**
  * @brief OPAMP1 Initialization Function
  * @param None
  * @retval None
  */
static void MX_OPAMP1_Init(void)
{
 
  /* USER CODE BEGIN OPAMP1_Init 0 */
 
  /* USER CODE END OPAMP1_Init 0 */
 
  /* USER CODE BEGIN OPAMP1_Init 1 */
 
  /* USER CODE END OPAMP1_Init 1 */
  hopamp1.Instance = OPAMP1;
  hopamp1.Init.PowerSupplyRange = OPAMP_POWERSUPPLY_LOW;
  hopamp1.Init.Mode = OPAMP_PGA_MODE;
  hopamp1.Init.NonInvertingInput = OPAMP_NONINVERTINGINPUT_DAC_CH;
  hopamp1.Init.InvertingInput = OPAMP_INVERTINGINPUT_IO0;
  hopamp1.Init.PgaGain = OPAMP_PGA_GAIN_2;
  hopamp1.Init.PowerMode = OPAMP_POWERMODE_NORMAL;
  hopamp1.Init.UserTrimming = OPAMP_TRIMMING_FACTORY;
  if (HAL_OPAMP_Init(&hopamp1) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN OPAMP1_Init 2 */
 
  /* USER CODE END OPAMP1_Init 2 */
 
}
 
/**
  * @brief GPIO Initialization Function
  * @param None
  * @retval None
  */
static void MX_GPIO_Init(void)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
 
  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOC_CLK_ENABLE();
  __HAL_RCC_GPIOA_CLK_ENABLE();
  __HAL_RCC_GPIOB_CLK_ENABLE();
 
  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(LED_GPIO_Port, LED_Pin, GPIO_PIN_RESET);
 
  /*Configure GPIO pin : B2_Pin */
  GPIO_InitStruct.Pin = B2_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_IT_RISING;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(B2_GPIO_Port, &GPIO_InitStruct);
 
  /*Configure GPIO pin : LED_Pin */
  GPIO_InitStruct.Pin = LED_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(LED_GPIO_Port, &GPIO_InitStruct);
 
}

[TDK]

Are you initializing clocks and pins within HAL_DAC_MspInit?

[BHM]

TDK,

I haven't changed HAL_DAC_MspInit(); here is the generated source. It does appear that the related clocks are initialized. Do I have to manually call this someplace? Or is it handled by HAL_DAC_Init()? There's no place in main that refers to this (or HAL_MspInit()).

Cheers,

Brett

void HAL_DAC_MspInit(DAC_HandleTypeDef* hdac)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
  if(hdac->Instance==DAC1)
  {
  /* USER CODE BEGIN DAC1_MspInit 0 */
 
  /* USER CODE END DAC1_MspInit 0 */
    /* Peripheral clock enable */
    __HAL_RCC_DAC1_CLK_ENABLE();
  
    __HAL_RCC_GPIOA_CLK_ENABLE();
    /**DAC1 GPIO Configuration    
    PA4     ------> DAC1_OUT1
    PA5     ------> DAC1_OUT2 
    */
    GPIO_InitStruct.Pin = GPIO_PIN_4|GPIO_PIN_5;
    GPIO_InitStruct.Mode = GPIO_MODE_ANALOG;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
 
  /* USER CODE BEGIN DAC1_MspInit 1 */
 
  /* USER CODE END DAC1_MspInit 1 */
  }
 
}

[TDK]

HAL_DAC_MspInit seems fine. You don't need to call it separately, it's called from within HAL_DAC_Init.

Not real sure what the problem is. I haven't spent a lot of time with the L4 series, or the OPAMP. Might be something unique to one of those.

[waclawek.jan]

Read our and check/post all relevant DAC/OPAMP/GPIO/SYSCFG/any other relevant registers content.

How do you write to DAC? Did you try DAC without OPAMP?

JW

[BHM · Accepted solution]

I figured out the problem, and it was indeed something simple that I was missing, but you can't tell it from the code. The code was fine. I was just probing the wrong pins on the Arduino Uno interface, because apparently I don't read schematics carefully. Thank you!