USART Rx & Tx communication code

[VDesa]

Hello,

I am a beginner to Nucleo-64 board programming and I am trying to work on USART communication of it. I am using NUCLEO-L476RG board and STM32CubeLL library for configuring USART and starting communication with it.

Programming Scenario:

I have connected Tx and Rx of USART2 together on the board. I want to transmit a string and receive the same string on the corresponding Rx pin. I have used interrupt based reception and I don't want to use DMA for it. I am getting the string on the Rx pin but the receive buffer is getting populated with the characters from aRxBuffer[2] position. Please help me to find the reason behind it.

My code:

void   SystemClock_Config(void);

void   Configure_GPIO(void);

void SendTo_USART(void);

void   Configure_USART(void);

uint8_t aTxBuffer[] = "TANTRAGYAAN";

uint8_t *tx=aTxBuffer;

uint8_t aRxBuffer[16]="";

uint8_t *rx=aRxBuffer;

int main(void)

{

 SystemClock_Config();

 Configure_GPIO();

Configure_USART();

SendTo_USART();

}

void SendTo_USART(void)

{

for (int index=0; index<11; index++)

{

LL_USART_TransmitData8(USART2,*(tx++));

while (!LL_USART_IsActiveFlag_TXE(USART2))

{

}

}

LL_USART_ClearFlag_TC(USART2);

}

void USART2_IRQHandler ( void )

{

while (!LL_USART_IsActiveFlag_RXNE(USART2))

{

} 

if (LL_USART_ReceiveData8(USART2)!='0'||0||"")

{

*(rx++)=LL_USART_ReceiveData8(USART2);

inc=inc+1;

LL_USART_ClearFlag_RTO(USART2);

}

}

void Configure_USART(void)

{

//LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOA);

LL_GPIO_SetPinMode(GPIOA, LL_GPIO_PIN_2, LL_GPIO_MODE_ALTERNATE); 

LL_GPIO_SetAFPin_0_7(GPIOA, LL_GPIO_PIN_2, LL_GPIO_AF_7);

 LL_GPIO_SetPinSpeed(GPIOA, LL_GPIO_PIN_2, LL_GPIO_SPEED_FREQ_HIGH);

 LL_GPIO_SetPinOutputType(GPIOA, LL_GPIO_PIN_2, LL_GPIO_OUTPUT_PUSHPULL);

 LL_GPIO_SetPinPull(GPIOA, LL_GPIO_PIN_2, LL_GPIO_PULL_UP);

LL_GPIO_SetPinMode(GPIOA, LL_GPIO_PIN_3, LL_GPIO_MODE_ALTERNATE);

 LL_GPIO_SetAFPin_0_7 (GPIOA, LL_GPIO_PIN_3, LL_GPIO_AF_7);

 LL_GPIO_SetPinSpeed(GPIOA, LL_GPIO_PIN_3, LL_GPIO_SPEED_FREQ_HIGH);

 LL_GPIO_SetPinPull(GPIOA, LL_GPIO_PIN_3, LL_GPIO_PULL_UP);

LL_APB1_GRP1_EnableClock(LL_APB1_GRP1_PERIPH_USART2);

LL_RCC_SetUSARTClockSource(LL_RCC_USART2_CLKSOURCE_PCLK1);

LL_USART_SetTransferDirection(USART2, LL_USART_DIRECTION_TX_RX);

LL_USART_EnableDirectionTx(USART2);

LL_USART_ConfigCharacter(USART2, LL_USART_DATAWIDTH_8B, LL_USART_PARITY_NONE, LL_USART_STOPBITS_1);

LL_USART_SetBaudRate(USART2, SystemCoreClock,LL_USART_OVERSAMPLING_16, 115200);

 LL_USART_SetHWFlowCtrl(USART2, LL_USART_HWCONTROL_CTS);

 LL_USART_SetOverSampling(USART2, LL_USART_OVERSAMPLING_16);

LL_USART_Enable(USART2);

NVIC_SetPriority(USART2_IRQn, 0);  

 NVIC_EnableIRQ(USART2_IRQn);

LL_USART_EnableIT_RXNE (USART2);

}

void SystemClock_Config(void)

{

 /* MSI configuration and activation */

 LL_FLASH_SetLatency(LL_FLASH_LATENCY_4);

LL_RCC_MSI_EnableRangeSelection();

LL_RCC_MSI_SetRange(LL_RCC_MSIRANGE_7);

 LL_RCC_MSI_Enable();

 while(LL_RCC_MSI_IsReady() != 1) 

 {

 };

 /* Main PLL configuration and activation */

 LL_RCC_PLL_ConfigDomain_SYS(LL_RCC_PLLSOURCE_MSI, LL_RCC_PLLM_DIV_1, 40, LL_RCC_PLLR_DIV_2);

 LL_RCC_PLL_Enable();

 LL_RCC_PLL_EnableDomain_SYS();

 while(LL_RCC_PLL_IsReady() != 1) 

 {

 };

 /* Sysclk activation on the main PLL */

 LL_RCC_SetAHBPrescaler(LL_RCC_SYSCLK_DIV_1);

 LL_RCC_SetSysClkSource(LL_RCC_SYS_CLKSOURCE_PLL);

 while(LL_RCC_GetSysClkSource() != LL_RCC_SYS_CLKSOURCE_STATUS_PLL) 

 {

 };

 /* Set APB1 & APB2 prescaler*/

 LL_RCC_SetAPB1Prescaler(LL_RCC_APB1_DIV_1);

 LL_RCC_SetAPB2Prescaler(LL_RCC_APB2_DIV_1);

 /* Set systick to 1ms in using frequency set to 80MHz */

 /* This frequency can be calculated through LL RCC macro */

 /* ex: __LL_RCC_CALC_PLLCLK_FREQ(__LL_RCC_CALC_MSI_FREQ(LL_RCC_MSIRANGESEL_RUN, LL_RCC_MSIRANGE_6), 

                 LL_RCC_PLLM_DIV_1, 40, LL_RCC_PLLR_DIV_2)*/

 LL_Init1msTick(80000000);

 /* Update CMSIS variable (which can be updated also through SystemCoreClockUpdate function) */

 LL_SetSystemCoreClock(80000000);

}

Please help me.

Thank you.

[VDesa]

Hi Pavel,

My task is to send some character string from Tx to Rx pin of same USART2. But, to the best of my knowledge, I think that during transmission, only a single character is taken from the string as the TDR register of Tx can hold only 1 byte. So, if I don't use interrupt and send all the characters, then Rx will not be able to sense the incoming characters and I don't see anything being updated in RxBuffer.

I have removed the below line. It was to check whether I am getting any of these characters in 2 subsequent iterations.

if (LL_USART_ReceiveData8(USART2)!='0'||0||"")

I hope my understanding is right and please correct me if I am wrong.

[VDesa]

I referred the below link:

https://stackoverflow.com/questions/46198829/stm32-hal-usart-receive-by-interrupt

[VDesa]

Hi waclawek,

I tried setting 4 MHz i.e., LL_RCC_MSIRANGE_6. But again the same problem. But this time the first 2 characters are getting repeated on 11th and 12th position in RxBuffer.

[VDesa]

Hi All,

When I forcefully assigned the aRxBuffer, like the one shown below, the code worked.

*(rx)=LL_USART_ReceiveData8(USART2);

aRxBuffer[inc]=*(rx);

But I don't understand why it was not taking automatically since rx is defined as pointer to the aRxBuffer.