UART DMA receive via RTOS

[Ala]

hey there

there is a simple question: how can I receive data on my UART in DMA mode using RTOS? recently I ran a project where I just get all the data right when they arrived using UART DMA. but not I what the whole process to be done using RTOS. how can I do that?

[KnarfB]

If you already have a cyclic DMA receive buffer, there are several options. If the serial data is more or less a countinous data stream you write a consumer task blocking on a semaphore or task event. You also implement the half-full+full handlers/callbacks and let them fire the semaphore/task event, thereby unblocking the task which can now process half of the DMA receive buffer.

You could further decouple the interrupts from the consumer task by using a queue.

If the serial data is only some spontaneous sending of few bytes, you can implement a consumer task having a timer/wait, periodically polling for new data.

Finally, you can combine both approaches.

hth

KnarfB

[Ala]

ok then I'll try.

an other question: what to do if I want a task to be done only once in main()?

[KnarfB]

A task can suspend itself and will never be scheduled again (unless Resumed by someone else). In addition, it might be also deleted but I somehow recall that there were issues with that.

[Ala]

dear KnarfB

here is my code

void SENDATTask(void const * arg)
{
	while(1)
	{
	
	if (Sim800_at_sendCommand("AT\r\n", 5000, (char*)SIM800.msg.buff, sizeof(SIM800.msg.buff), 1, "\r\nOK\r\n") == 1)
	{
		osDelay(500);
		HAL_IWDG_Refresh(&hiwdg); //Reload Watchdog inorder to prevent Micro Reset	
	}
			
	}
	vTaskDelete(SENDATTaskHandle);
	vTaskSuspend(SENDATTaskHandle);
		}
}

eigther I use vTaskDelete() or vTaskSuspend(), the task continues to run... why is that?

[KnarfB]

maybe the MCU resets and restarts because you stopped feeding the watchdog?

[Ala]

HELP:

I added some tasks to just check state of a pin, but what happens is that the scheduler stucks in the task of UART receive... why? I mean the added task do not need any resources and all of them have same priority...

void UARTTask(void const * arg)
{
		while(1)
		{
			 HAL_IWDG_Refresh(&hiwdg); //Reload Watchdog inorder to prevent Micro Reset	
				UartDataRec_FUN();
		}
}
 
void SEND_Initial_AT_Task(void const * arg)
{
		while(1)
		{
 
 //stuff that I mentioned in privious posts ....
	}
	vTaskSuspend(SEND_Initial_AT_TaskHandle);
		}
}
 
void CheckAntenna_Task(void const * arg)
{
		while(1)
		{
			 HAL_IWDG_Refresh(&hiwdg); //Reload Watchdog inorder to prevent Micro Reset	
				CheckAntenna();
		}
}

it doesn't go through CheckAntenna_Task() and stucks in UARTTask() where it receives via UART DMA, whyyyyy????

[Tilen MAJERLE]

Usually application isn't aware of length of data to receive. You may implement the approach as described on Github article:

https://github.com/MaJerle/stm32-usart-uart-dma-rx-tx

In a nutshell, it works like this:

• DMA TC and HT events are writing to message queue
• UART IDLE is writing to message queue
• dedicated thread is waiting for data from message queue and does processing of the data
• Process repeats forever