STM32, the program does not enter the "IF" condition to check pin state

Question

I'm new to STM32, and I want to write a function that will check if the sensor (DHT11) has sent data. I set PA6 to OUTPUT mode and hold low for at least 18ms (according to datasheet), and then release it and set PA6 to INPUT mode, then external interrupt (IT_RISING mode) on pin PA5 is triggered. Then the simple cycle checks PA5 pinstate for some time (because DHT11, if connected properly, will pull down the line multiple times). If the DHT11 is not connected, then the PA5 will be high all the time. But when I test the program in Proteus, only "else" condition always enabled... I've tried multiple methods (IDR, HAL, CMSIS, macros), but no one of them didn't solve the problem. Where is the mistake?

The interrupt function is:

volatile uint32_t check_cnt = 0, check_delay = 100;
void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin) {
 if (GPIO_Pin == GPIO_PIN_5) {
 while (check_cnt < check_delay) {
 if (GPIOA->IDR & (0 << 5)) { //CHECK PA5 PINSTATE (if low, then DHT11 have send data)
 GPIOA->BSRR = (1 << 8); //line, that shows DHT11 connected
 break;
 } else {
 GPIOA->BSRR = (1 << 9); //line, that shows DHT11 disconnected
 check_cnt++;
 }
 }
 }
 HAL_NVIC_DisableIRQ(EXTI9_5_IRQn);
}

GPIO Init function:

void MX_GPIO_Init(void) {
 GPIO_InitTypeDef GPIO_InitStruct = { 0 };
 __HAL_RCC_GPIOA_CLK_ENABLE();
 __HAL_RCC_USART2_CLK_ENABLE();
 HAL_GPIO_WritePin(GPIOA, GPIO_PIN_1, GPIO_PIN_RESET);
 GPIO_InitStruct.Pin = GPIO_PIN_1 | GPIO_PIN_8 | GPIO_PIN_9 | GPIO_PIN_11 | GPIO_PIN_12;
 GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
 GPIO_InitStruct.Pull = GPIO_NOPULL;
 GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
 HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
 GPIO_InitStruct.Pin = GPIO_PIN_5;
 GPIO_InitStruct.Mode = GPIO_MODE_IT_RISING;
 GPIO_InitStruct.Pull = GPIO_NOPULL;
 GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
 HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
 __HAL_GPIO_EXTI_CLEAR_IT(GPIO_PIN_5);
 HAL_NVIC_SetPriority(EXTI9_5_IRQn, 0, 0);
 HAL_NVIC_EnableIRQ(EXTI9_5_IRQn);
}

DHT11 Init function:

void DHT11_Init(void) {
 GPIO_InitTypeDef GPIO_InitStruct = { 0 };
 __HAL_RCC_GPIOA_CLK_ENABLE();
 GPIO_InitStruct.Pin = GPIO_PIN_6;
 GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
 GPIO_InitStruct.Pull = GPIO_NOPULL;
 GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
 HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
 GPIOA->BSRR = (0 << 6);
 HAL_Delay(18);
 GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
 HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
}

main.c

int main(void) {
 HAL_Init();
 SystemClock_Config();
 MX_GPIO_Init();
 //MX_USART2_UART_Init();
 //DWT_Init();
 DHT11_Init();
 HAL_GPIO_EXTI_Callback(GPIO_PIN_5);
 while(1)
 {
 //other code
 }
}

DHT11 connected

DHT11 disconnected

Scheme

• brhans: if (GPIOA->IDR & (0 << 5)) will always evaluate to false because 0 << 5 will always be 0. You probably meant 1 << 5 there.
• brhans: Or even better - use the GPIO_PIN_5 which you already used on the line above.

Answer 1

This is not about STM32 but purely C mistake.

Anding anything with a 0 results in 0 so the comparison result is never true.