Usart idle interrupt question

[PZhou.1]

Hello,

When I enable usart idle interrupt function on stm32g071rb, it fires the interrupt immediately even there is no communication on the bus.

I debug use cubeide and IAR. The results are the same.

When UE bit in USART_CR1set to 1, the IDLE bit in USART_ISR will change to 1 right now.

So after IDLE interrupt enabled, it will cause a interrupt.

I don't know why the IDLE bit in USART_ISR change to 1.

And I try to clear the IDLE bit in USART_ISR, by set IDLECF bit in USART_ICR before enable the interrupt. It no works.

But I add a delay_1_ms between uart_init and clear Idle interrupt flag, it works.

The code is below:

 MX_USART1_UART_Init();

 MX_USART2_UART_Init();

 /* USER CODE BEGIN 2 */

 HAL_Delay(1); // work with this

 __HAL_UART_CLEAR_IDLEFLAG(&huart1);

 __HAL_UART_CLEAR_IDLEFLAG(&huart2);

 __HAL_UART_ENABLE_IT(&huart1, UART_IT_IDLE);

 __HAL_UART_ENABLE_IT(&huart2, UART_IT_IDLE);

[Piranha]

Well, it does signal that the line has entered the IDLE condition. What is the problem here?

[PZhou.1]

The problem is that there is no communication on the uart receive line. So it doesn't need the condition for idle interrupt.

Even I clear the interrupt flag before enable this interrupt, it seems the flag can't be cleared.

I must add a delay, later the problem disappear.

[TDK]

Possibly it doesn't trigger an idle condition until the first definitive stop bit is received, which would occur around 10 or so bits after initialization.

[S.Ma]

Check the sequence between gpio and usart init. if gpio is done later, for a short while the usart is exposed to the unknown floating node.... strike throught this concern by checking it.

[PZhou.1]

Thanks for reply.

My doubt is same as you.

The init of usart is create by cubeIDE use HAL lib. I think the procedure are same between F103 and G071. Same code in F103 and G071, the phenomenon

are different. F103 is OK, but G071 is not. It confused me.

[PZhou.1]

Thanks for reply.

The problem is that it trigger an idle condition without a communication.

[VL.3]

Hey!

Sorry for reviving an old topic, I found the same behaviour. Chip is STM32G4. Here is my receive code:

void usart_start_reception(void)
{
    LL_DMA_DisableChannel(DMA1, LL_DMA_CHANNEL_1); // Do not Clear Channel global interrupt flag when the channel in ON. bug id 2.3.1 in Product Errata Sheet.
    LL_DMA_ClearFlag_GI1(DMA1);
    LL_DMA_SetDataLength(DMA1, LL_DMA_CHANNEL_1, sizeof(usart_rx_dma_buffer));

    LL_DMA_EnableIT_TC(DMA1, LL_DMA_CHANNEL_1);
    LL_DMA_EnableIT_TE(DMA1, LL_DMA_CHANNEL_1);
    LL_DMA_EnableChannel(DMA1, LL_DMA_CHANNEL_1);

    LL_USART_EnableIT_PE(USART1);
    LL_USART_EnableIT_ERROR(USART1);
    LL_USART_EnableDMAReq_RX(USART1);
    LL_USART_ClearFlag_IDLE(USART1);
    LL_USART_EnableIT_IDLE(USART1);
}

And here's Cube generated USART initialisation:

void MX_USART1_UART_Init(void)
{
//...
  LL_USART_Enable(USART1);

  /* Polling USART1 initialisation */
  while((!(LL_USART_IsActiveFlag_TEACK(USART1))) || (!(LL_USART_IsActiveFlag_REACK(USART1))))
  {
  }
  /* USER CODE BEGIN USART3_Init 2 */
    LL_mDelay(1);
    usart_start_reception();
  /* USER CODE END USART3_Init 2 */
}

I noticed that without an artificial 1ms delay, the USART IDLE interrupt will fire the first time even without any data on the rx line.