UART: Reception using Interrupts

The next example receive a string of character using interrupts, in this case we define a message as any string of characters ending with a ‘\r' character, we configure the interrupt reception to be triggered by one character using HAL_UART_Receive_IT function, then in the callback each byte received is placed in a buffer until the '\r', after that we set the flag indicating a message has arrived.

#include "bsp.h"
#include <string.h>

uint8_t RxBuffer[ 10 ];       /*buffer for message received*/
uint8_t RxByte;               /*temporary reception buffer*/
__IO ITStatus stat = RESET;   /*flag to indicate a message has been received*/
UART_HandleTypeDef UartHandle; /*uart handler*/

int main( void )
{
    GPIO_InitTypeDef GPIO_InitStruct; /*gpio init structure*/
    
    HAL_Init(); /*init cube library*/
    
    __HAL_RCC_GPIOC_CLK_ENABLE(); /*enable clock on port C*/

    /*config pins 0, 1 y 2 from port C as output push-pull*/
    GPIO_InitStruct.Pin = GPIO_PIN_0 | GPIO_PIN_1 | GPIO_PIN_2;
    GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
    /*set configuration*/
    HAL_GPIO_Init( GPIOC, &GPIO_InitStruct );
    
    /*uart configuration options for module USART2, 9600 baudrate,
    8bits, 1 stop bit, no parity, no flow control, and 8 bit lenght */
    UartHandle.Instance         = USART2;
    UartHandle.Init.BaudRate    = 9600;
    UartHandle.Init.WordLength  = UART_WORDLENGTH_8B;
    UartHandle.Init.StopBits    = UART_STOPBITS_1;
    UartHandle.Init.Parity      = UART_PARITY_NONE;
    UartHandle.Init.HwFlowCtl   = UART_HWCONTROL_NONE;
    UartHandle.Init.Mode        = UART_MODE_TX_RX;
    UartHandle.Init.OverSampling = UART_OVERSAMPLING_16;
    /*init uart2 with previous paramters*/
    HAL_UART_Init( &UartHandle );

    /*Set reception through interrupt of one character*/
    HAL_UART_Receive_IT( &UartHandle, &RxByte, 1 );

    while(1)
    {
        if( stat == SET ) /*a message has been recieved*/
        {
            stat = RESET; /*clear reception flag*/
            if( memcmp("one\r", RxBuffer, sizeof("one\r")-1) == 0 )
            { 
                /* toggle C0 if it was "one" string */
                HAL_GPIO_TogglePin( GPIOC, GPIO_PIN_0 );
            }
            else if( memcmp("two\r", RxBuffer, sizeof("two\r")-1) == 0 )
            { 
                /* toggle C1 if it was "two" string */
                HAL_GPIO_TogglePin( GPIOC, GPIO_PIN_1 );
            }
            else if( memcmp("three\r", RxBuffer, sizeof("three\r")-1) == 0 )
            { 
                /* toggle C2 if it was "three" string */
                HAL_GPIO_TogglePin( GPIOC, GPIO_PIN_2 );
            }
        }
    }
}

/*This function is called everytime a new byte is received, the code in it stores the bytes
in the buffer RxBuffer and detects when the '\r' signaling the end of a string*/
void HAL_UART_RxCpltCallback( UART_HandleTypeDef *huart )
{
    static uint32_t i = 0;
    RxBuffer[i] = RxByte;       /*store data*/
    i++;                        /*increase index pointer*/
    
    /*look for the end of the string*/
    if( RxBuffer[i-1] == '\r' ) 
    {
        stat = SET;         /*set flag to indicate reception complete*/
        RxBuffer[i] = '\0'; /*set end of the string*/
        i = 0;              /*restart buffer index*/
    }
    /*Set reception through interrupt of one character again*/
    HAL_UART_Receive_IT( &UartHandle, &RxByte, 1 );
}

msps.c

/*The function is called from HAL_UART_Init at the very beginning
and allows us to set the pins to be used as serial port*/
void HAL_UART_MspInit( UART_HandleTypeDef *huart )
{
    GPIO_InitTypeDef GPIO_InitStruct; /*gpios init structure*/
    
    __HAL_RCC_USART2_CLK_ENABLE();    /*enable usart2 clock*/
    __HAL_RCC_GPIOA_CLK_ENABLE();     /*eneable port A clock */
    
    /*set pin 2(tx) and pin 3(rx) from port A in altern mode usart2
    the altern mode info can be found in device datasheet*/
    GPIO_InitStruct.Pin   = GPIO_PIN_2 | GPIO_PIN_3;
    GPIO_InitStruct.Mode  = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull  = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
    GPIO_InitStruct.Alternate = GPIO_AF1_USART2;
    /*apply configuration configuracion*/
    HAL_GPIO_Init( GPIOA, &GPIO_InitStruct );
    
    /*enable UART vector interrupt with priority of 1*/
    HAL_NVIC_SetPriority( USART2_LPUART2_IRQn, 1, 0 );
    HAL_NVIC_EnableIRQ( USART2_LPUART2_IRQn );
}

ints.c

extern UART_HandleTypeDef UartHandle;

/*Declare interrupt service rutine as it is declare in startup_stm32g0b1xx.s file,
the program will jump here every time a byte has been transmitted*/
void USART2_LPUART2_IRQHandler( void )/*vector de interrupcion usart2*/
{
    /*HAL library fucntion that attend interrupts on UART module*/
    HAL_UART_IRQHandler( &UartHandle );
}