extern "C"

[Amrello]

Hello everyone, maybe it's a stupid question but in interrupt handling function I can't rewrite a variable. I'm sure that the interrupt is triggered and assigns a value to var, read_msg function is executed in a loop, but when the value of a variable is checked, it is always equal zero.

  uint8_t var;

extern "C" void USART1_IRQHandler(void)
{
    var = 1;
    if(USART_GetITStatus(USART1, USART_IT_RXNE) == SET)
    {
        if ((USART1->SR & (USART_FLAG_NE|USART_FLAG_FE|USART_FLAG_PE|USART_FLAG_ORE)) == 0) // check for errors
        {
            rx1_buffer[rx1_wr_index++]= (uint8_t) (USART_ReceiveData(USART2)& 0xFF);
            if (rx1_wr_index == RX_BUFFER_SIZE) rx1_wr_index=0;
            if (++rx1_counter == RX_BUFFER_SIZE)
            {
                //rx1_counter=0;
                rx1_buffer_overflow=1;
            }
        }
        else USART_ReceiveData(USART2); // read data even if there is an error
        //DrawChar(100, 100, TFT_BLUE, TFT_BLACK, (const uint8_t*) font8x8, '1', 10);
    }
}



void read_msg()
{
    uint8_t data;
    if(var == 1)
    {
        USART_ITConfig(USART2, USART_IT_RXNE, DISABLE);
        data=rx1_buffer[rx1_rd_index++];
        DrawChar(100, 100, TFT_BLUE, TFT_BLACK, (const uint8_t*) font8x8, 'g', 10);
        USART_ITConfig(USART2, USART_IT_RXNE, ENABLE);
    }
}

[dhayden]

You need to declare var as volatile uint8_t var;. Otherwise the compiler thinks it doesn't change and optimizes accordingly.

[Amrello]

I've tried it before, it also does not work

[Jaybob66]

initialise it first, then you'll know for sure if the ISR was called.
volatile uint8_t var(55)


have you set a breakpoint in the ISR to determine if its really being called?