STM32 UART Interrupt between 2 STM32F103C8 boards.

[RSy.1]

Hello guys good day. I would like to ask for your suggestions regarding the UART interrupt between 2 STM32F103C8 MCUs. I can transmit and receive between 2 MCUs using a single input and output with the use of the IRQHandler. However when I wanted to use the 2nd pin and output I could not transmit and receive anymore. So basically the interrupt is only working for a single inputt/output but for multiple input/output it does not work anymore. I have the codes below:

 // I defined this function  before the main
void UARTTX(uint8_t data)                                     
{
	while(!(USART2 -> SR & USART_SR_TXE));
	USART2 -> DR = data;
}
 
// I defined this function  before the main
char UARTRX()                                                         
{
	while(!(USART2 -> SR & USART_SR_RXNE));
	return USART2 -> DR;
}
 
.
.
.
 
 // I enabled these registers before the while loop
USART2 -> CR1 |= USART_CR1_UE;              
USART2 -> CR1 |= USART_CR1_TE;
USART2 -> CR1 |= USART_CR1_RE;
USART2 -> CR1 |= USART_CR1_RXNEIE;
USART2 -> CR1 |= USART_CR1_TXEIE;
 
.
.
.
 
//main code is in the IRQHandler
void USART2_IRQHandler(void)                                               
{
 HAL_UART_IRQHandler(&huart2);
 {
  //this is first tx output.  This code is working only if the second tx output below is not enabled
 if(!HAL_GPIO_ReadPin(BUTTON1_GPIO_Port, BUTTON1_Pin))                                                                                                                            
    {
	USART2 -> DR = 0xFF;																					
    }
  else 
    {
	USART2 -> DR = 0x00;																					
    }
}
	 //this is 2nd tx input and not working                                                                                                    	
//	{
//	 if(HAL_GPIO_ReadPin(BUTTON2_GPIO_Port, BUTTON2_Pin))                       
//	 {
//		USART2 -> DR = 0xF0;																					
//	}
//	else			
//	{
//		USART2 -> DR = 0x0F;																					
//	}
//	}
 
 // this is first rx input  and only working if 2nd rx input below is disabled	 
{	
	if(USART2 -> DR == 0xFF)                                    
	{
		HAL_GPIO_WritePin(LED1_GPIO_Port, LED1_Pin, GPIO_PIN_SET);
	}
	else if(USART2 -> DR == 0x00)
	{
		HAL_GPIO_WritePin(LED1_GPIO_Port, LED1_Pin, GPIO_PIN_RESET);
	}
}
 
  //this is 2nd rx input and is not working
//	{	
//	if(USART2 -> DR == 0xF0)                                                       
//	{
//	HAL_GPIO_WritePin(LED2_GPIO_Port, LED2_Pin, GPIO_PIN_SET);
//	}
//	else if(USART2 -> DR == 0x0F)
//	{
//	HAL_GPIO_WritePin(LED2_GPIO_Port, LED2_Pin, GPIO_PIN_RESET);
//	}
//	}	
}
 
 
 

[Tesla DeLorean]

Read the USART2->DR *ONCE* into a variable, and then inspect the variable

The IRQ will occur ONCE for each byte received, if you need to process a sequence, add a state-machine so you can step through the different states as each byte is received.

[RSy.1]

Good day Sir thank you for the answer. I am confused by what you mentioned ONCE. What do you mean by this and how is this written?

[Tesla DeLorean]

It is a register, it does not behave like RAM. Think of it like a ratcheting sprocket, every time you read the content the machine advances.

{

uint8_t dr = USART2 -> DR; // READ IT ONCE

if(dr == 0xFF) // Compare against the local copy

{

HAL_GPIO_WritePin(LED1_GPIO_Port, LED1_Pin, GPIO_PIN_SET);

}

else if(dr == 0x00)

{

HAL_GPIO_WritePin(LED1_GPIO_Port, LED1_Pin, GPIO_PIN_RESET);

}

}

Also this is really inefficient in a load/store architecture, with volatile register accesses that the compiler/optimize cannot fold

 // I enabled these registers before the while loop

USART2 -> CR1 |= USART_CR1_UE;

USART2 -> CR1 |= USART_CR1_TE;

USART2 -> CR1 |= USART_CR1_RE;

USART2 -> CR1 |= USART_CR1_RXNEIE;

USART2 -> CR1 |= USART_CR1_TXEIE;

[RSy.1]

Thank you Sir for the hint. Im not sure why still only 1 output is activated. I still need to do a lot of reading :)

[RSy.1]

@Community member​  I combined the codes this way as you advised but still not working. What is wrong here?

Also what about for the Transmit part? Do I have to define a common variable and compare them?

{
 
uint8_t dr = USART2 -> DR; // READ IT ONCE
 
if(dr == 0xFF) // Compare against the local copy
 
{
 
HAL_GPIO_WritePin(LED1_GPIO_Port, LED1_Pin, GPIO_PIN_SET);
 
}
 
else if(dr == 0x00)
 
{
 
HAL_GPIO_WritePin(LED1_GPIO_Port, LED1_Pin, GPIO_PIN_RESET);
 
}
if(dr == 0xF0) 
 
{
 
HAL_GPIO_WritePin(LED2_GPIO_Port, LED2_Pin, GPIO_PIN_SET);
 
}
 
else if(dr == 0x0F)
 
{
 
HAL_GPIO_WritePin(LED2_GPIO_Port, LED2_Pin, GPIO_PIN_RESET);
 
}
 
}

[Tesla DeLorean]

The way you have interrupts enabled it will probably enter continously.

You should check the TXE bit in the SR before sending. And for RXNE before reading.​

Not sure I'd call the HAL handler for a register level test.​

[RSy.1]

Thank you Sir now it's working fine. For now I can transmit multiple data from MCU1 to MCU2. MCU1 transmits and MCU2 receives. I use a single IRQHandler to do this. However I am having issues when I use the same IRQHandler to do both transmit and receive at the same time with multiple data.

[Tesla DeLorean]

You can't wait around in the handler for subsequent bytes.

You need to buffer, and index through an array, advancing at each entry.​