STM32F407VG Custom Break over UART1 for DMX transmitting

[PUrsu.1]

Hi everyone,

I am trying to output DMX data over UART1 at 25Hz. Therefore I need a break for 88us. My plan was to take control over the port and set it into GPIO Mode. After 88us I set it back to UART mode.

For breaktimes > 250us it works fine. But below that value the voltage spike only goes to roundabout 800mV. What am I doing wrong?

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim){
	if(htim == &htim3) {
		    setGPIOMode();
		    // wait 88 microseconds for the DMX break
		    delay_us(88);
		   setUartMode();
 
		    // wait 8 microseconds for the MAB (Mark After Break)
		    delay_us(8);
	}
}

void setGPIOMode() {
	GPIOA->MODER = (GPIOA->MODER & ~GPIO_MODER_MODER9_Msk) | (1 << GPIO_MODER_MODER9_Pos);
}
 
void setUartMode() {
	GPIOA->MODER = (GPIOA->MODER & ~GPIO_MODER_MODER9_Msk) | (2 << GPIO_MODER_MODER9_Pos);
}
void delay_us (uint16_t us)
{
 
	__HAL_TIM_SET_COUNTER(&htim2,0);  // set the counter value a 0
	while (__HAL_TIM_GET_COUNTER(&htim2) < us);  // wait for the counter to reach the us input in the parameter
}

static void MX_USART1_UART_Init(void)
{
 
  /* USER CODE BEGIN USART1_Init 0 */
 
  /* USER CODE END USART1_Init 0 */
 
  /* USER CODE BEGIN USART1_Init 1 */
 
  /* USER CODE END USART1_Init 1 */
  huart1.Instance = USART1;
  huart1.Init.BaudRate = 250000;
  huart1.Init.WordLength = UART_WORDLENGTH_8B;
  huart1.Init.StopBits = UART_STOPBITS_2;
  huart1.Init.Parity = UART_PARITY_NONE;
  huart1.Init.Mode = UART_MODE_TX;
  huart1.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart1.Init.OverSampling = UART_OVERSAMPLING_16;
  if (HAL_UART_Init(&huart1) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN USART1_Init 2 */
  /* USER CODE END USART1_Init 2 */
 
}

static void MX_TIM2_Init(void)
{
 
  /* USER CODE BEGIN TIM2_Init 0 */
 
  /* USER CODE END TIM2_Init 0 */
 
  TIM_ClockConfigTypeDef sClockSourceConfig = {0};
  TIM_MasterConfigTypeDef sMasterConfig = {0};
 
  /* USER CODE BEGIN TIM2_Init 1 */
 
  /* USER CODE END TIM2_Init 1 */
  htim2.Instance = TIM2;
  htim2.Init.Prescaler = 83;
  htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim2.Init.Period = 4294967295;
  htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  htim2.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
  if (HAL_TIM_Base_Init(&htim2) != HAL_OK)
  {
    Error_Handler();
  }
  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
  if (HAL_TIM_ConfigClockSource(&htim2, &sClockSourceConfig) != HAL_OK)
  {
    Error_Handler();
  }
  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
  if (HAL_TIMEx_MasterConfigSynchronization(&htim2, &sMasterConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN TIM2_Init 2 */
 
  /* USER CODE END TIM2_Init 2 */
 
}
 
/**
  * @brief TIM3 Initialization Function
  * @param None
  * @retval None
  */
static void MX_TIM3_Init(void)
{
 
  /* USER CODE BEGIN TIM3_Init 0 */
 
  /* USER CODE END TIM3_Init 0 */
 
  TIM_ClockConfigTypeDef sClockSourceConfig = {0};
  TIM_MasterConfigTypeDef sMasterConfig = {0};
 
  /* USER CODE BEGIN TIM3_Init 1 */
 
  /* USER CODE END TIM3_Init 1 */
  htim3.Instance = TIM3;
  htim3.Init.Prescaler = 55;
  htim3.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim3.Init.Period = 59999;
  htim3.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  htim3.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
  if (HAL_TIM_Base_Init(&htim3) != HAL_OK)
  {
    Error_Handler();
  }
  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
  if (HAL_TIM_ConfigClockSource(&htim3, &sClockSourceConfig) != HAL_OK)
  {
    Error_Handler();
  }
  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
  if (HAL_TIMEx_MasterConfigSynchronization(&htim3, &sMasterConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN TIM3_Init 2 */
 
  /* USER CODE END TIM3_Init 2 */
 
}

 

[waclawek.jan]

Where and how do you measure that voltage? Can you show oscilloscope screenshots for the two different cases?

JW

[PUrsu.1]

Hey Jan,

sure! Here are pictures with the delay set to 80us / 3000us.

[waclawek.jan]

Can't this be just your oscilloscope's limitation?

Do you measure after some optocoupler? If yes, try measuring directly on mcu pin.

JW

[PUrsu.1]

Hey Jan,

I also had this thought. But toggling a normal GPIO pin with 80us delay in between works fine and the oscilloscope (100MHz 1GSa/s) displays the correct voltage (around 3,3V). I am measuring directly on the pin.

//I tried this code and the voltage of PD9 is at arround 300mV, the voltage of the oszi_Pin is at 3,3V
 
HAL_GPIO_TogglePin(oszi_GPIO_Port, oszi_Pin);
setGPIOMode();
delay_us(88);
setUartMode();
HAL_GPIO_TogglePin(oszi_GPIO_Port, oszi_Pin);
delay_us(88);

[waclawek.jan]

Tx on PA9 at 250kBaud works normally? at 250kBaud, one bit is 4us, if you transmit something like 0x55, do you see individual bits?

How is GPIO_OSPEEDR set for PA9? GPIO_ODR is set to 0 for PA9, I presume; but maybe you should read out the GPIOA registers and post them here.

Do you use OTG_FS?

JW

[PUrsu.1]

Hey Jan,

I should have probably mentioned that I'm using a STM32F407 discovery board. I found out that UART2 works fine for my purposes. I think that there must be any components on the board which disturb USART1. Could that be possible?

[PUrsu.1]

Hey Jan,

thank you for your help. I can now successfully output DMX.

Edit for others with probably the same problem:

I figured out that there is a problem on the STM32F407 Discovery board when trying to use UART1. Using another UART solved the problem for me. I think there are some components on the PCB which cause problems with higher baud rates on UART1.

I have another question (I don't know if I should open another thread for that). I now have one DMX output. My goal is to output way more data (8 DMX ports). Where should I begin researching this "multi" task? Just outputting the universes one after one should be too slow in my thought.

Is FreeRTOS the way to go for?

[DEdwi.1]

@PUrsu.1​ Would you consider using the PWM to generate the DMX512 signal ? there seems to be a lot of timers on the STM32F407 which can be used for PWM outputs