Why I can't change variable in it.c?

Question

I have stm32vldiscovery project. I want to use external interrupt by PA0 (user button). When I press the button (PA0), then function EXTI0_IRQHandler must set ldOn equal 0. But ldOn always is 1. Debuger shows what function EXTI0_IRQHandler runned on. ldOn change value to 0, and again stay equal 1. Why? Have this code: main.c

#include "main.h"
...
uint8_t ldOn = 1;

int main(void)
{

  HAL_Init();

  SystemClock_Config();

  MX_GPIO_Init();
  HAL_GPIO_WritePin(LD4_GPIO_Port, LD4_Pin, GPIO_PIN_SET);

  while (1)
  {
        if(ldOn == 0)
            HAL_GPIO_WritePin(LD4_GPIO_Port, LD4_Pin, GPIO_PIN_RESET);
  }
}

it.c

#include "main.h"
...
extern uint8_t ldOn;
void EXTI0_IRQHandler(void)
{
  ldOn = 0;
  HAL_GPIO_EXTI_IRQHandler(GPIO_PIN_0);
}

When I used stm32f4-disc1 board, this construction works perfectly...

Answer 1

Either declare variable ldOn as volatile or Remove optimizations from compilation and check

It should work. Even after using volatile keyword/removing optimization from compilation if code is not working then you have to triple review your code and check whether somewhere else variable is being modified.

Check this link