Error Transmitting data via UART when using ADC & DMA (works separately)

[ponuliukas]

Hi All,

I have been a little confused about my code and would appreciate some help greatly...

I have a basic program where I would like to read the ADC values from a sensor, and transmit them via UART for later signal processing and whatnot.

The structure is simple, and when I tested out reading the values from the ADC, as well as sending strings via UART - they both work perfectly fine. But now when I merge the two, the UART does not work anymore... I do not see anything in my serial monitor (Putty)

I feel like I am missing something big, but cannot find it. I would appreciate it if someone pointed me in the right direction :)

in my main, I have: 

uint32_t value[2]; // start adc in DMA mode
int isSent = 1;
uint8_t tx_buffer[] = "Welcome to BinaryUpdates!\n\r"; 

int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_ADC1_Init();
  MX_TIM3_Init();
  MX_TIM4_Init();
  MX_TIM2_Init();
  MX_USART6_UART_Init();

  HAL_ADC_Start_DMA(&hadc1, value, 2);

  while (1)
  {
	  if (isSent == 1)
	      {
	  	  HAL_UART_Transmit_DMA(&huart6, tx_buffer, 27);
//       HAL_UART_Transmit_DMA(&huart6, value[0], sizeof(value[0]));
	  	  isSent = 0;
	      }
	      HAL_Delay(1000);
  }
}

void HAL_UART_TxCpltCallback(UART_HandleTypeDef *huart)
{
	isSent = 1;
}

[Andrew Neil]

---

@ponuliukas wrote:

the UART does not work anymore... 

---

What do you mean by that?

• It transmits nothing at all ?
• It transmits something, but not what you wanted ?
• other ?

EDIT:

You haven't shown your definition of isSent, but it should be 'volatile'

Do you have any conflicts between ADC and UART pins?

[raptorhal2]

Edit: Cancel - I misunderstood. How do you get "value" into tx_buffer ?

[Andrew Neil]

---

@ponuliukas wrote:

uint8_t tx_buffer[27] = "Welcome to BinaryUpdates!\n\r"; 

---

Although it doesn't matter in the code you've shown so far, note that this does not leave space for a terminating NUL - so that won't be a proper C string.

To have a proper C string:

uint8_t tx_buffer[] = "Welcome to BinaryUpdates!\n\r"; 

[ponuliukas]

Thank you for the reply @Andrew Neil and @raptorhal2 , and apologies for not being perfectly clear. I edited the question :) 

[Andrew Neil]

It's confusing to edit the question after people have already commented on the question in its original form!

It's better to post an update as a reply.

Again,  isSent should be 'volatile'

---

@ponuliukas wrote:

the UART does not work anymore... I do not see anything in my serial monitor (Putty) 

---

That could be because your UART is sending something that's not visible to PuTTY ?

Have you check on the wires with a logic analyser or oscilloscope?

You're ignoring the return value from HAL_UART_Transmit_DMA - it might be telling you something ...

https://community.st.com/t5/stm32-mcus-boards-and-hardware/hal-rcc-oscconfig/m-p/674455/highlight/true#M19028 

What happens if you do away with the DMA, and just use a plain blocking send?

[raptorhal2]

"value" is in binary, you will have to covert it to ASCII characters to be displayed by Putty. Think printf, or make your own conversion.

[ponuliukas]

Good to know, will do that from now on :) 

When I just use UART I see the text "Welcome to Binaryupdates". It is only when I uncomment:

HAL_ADC_Start_DMA(&hadc1, value, 2);

do I stop seeing anything in my serial monitor.

I have not checked with a logic analyzer nor an oscilloscope :(  I Do not have an access to one unfortunately... 

Same thing happens if I just use "HAL_UART_Transmit" - It works alone, but If I start the ADC DMA, it doesn't work...

@raptorhal2 at this point, I would like to start by just sending the 27 characters (Welcome to BinaryUpdates!) to confirm that I can send data via uart and read the sensor values at the same time. 

[Andrew Neil]

Check for any conflicts between ADC and UART pins?

[ponuliukas]

Doesn't look like there could be any conflict. I will scrutinize the PCB itself more