STM32 Timer Interrupt unexpected behavior - timer

Question

I want to implement long-press button to turn a device on.
I use external interrupt button to launch the timer on press, and stop and reset it on release of the button. If you hold the button enough (1 sec) it will call a Timer_Update event and turn on LED.
However, when I load my code to the Discovery and press reset, the first press of the user button lights the LED immediately as if the interrupt is generated at the very first launch of the Timer. Then it works properly - changes LED state if you hold the button for >= 1sec.
Project is generated via CubeMX
This is button interrupt handler
void EXTI0_IRQHandler(void)
{
/* USER CODE BEGIN EXTI0_IRQn 0 */
static uint8_t is_pressed = 0;
/* USER CODE END EXTI0_IRQn 0 */
HAL_GPIO_EXTI_IRQHandler(GPIO_PIN_0);
/* USER CODE BEGIN EXTI0_IRQn 1 */
if (!is_pressed) {
HAL_TIM_Base_Start_IT(&htim7);
HAL_GPIO_TogglePin(GPIOG, GPIO_PIN_13);
is_pressed = 1;
}
else {
HAL_GPIO_TogglePin(GPIOG, GPIO_PIN_13);
HAL_TIM_Base_Stop_IT(&htim7);
__HAL_TIM_SET_COUNTER(&htim7, 0);
is_pressed = 0;
}
/* USER CODE END EXTI0_IRQn 1 */
}
This is Timer interrupt handler
void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
HAL_GPIO_TogglePin(GPIOG, GPIO_PIN_14);
HAL_TIM_Base_Stop_IT(htim);
__HAL_TIM_SET_COUNTER(htim, 0);
}
The trigger event for the Timer in CubeMX is set as "Update Event"

Answer 1

Well it is a bug in the generated code. During timer initialization the call TIM_Base_SetConfig is called. This call has as a side effect that update interrupt bit is set in the SR. This means that when interrupt are enable in the HAL_TIM_Base_Start_IT immediately an interrupt is generated. This is what you are experiencing. See also https://www.youtube.com/watch?v=3yvY7pLMHAg 5:40. There also a HAL compatible fix is explained.

Answer 2

I would recommend the following implementation:
Setup EXTI pin for rising and falling edges
Check pin state in interrupt handler(instead of is_pressed variable)
EXTI handler can be implemented like below:
#define BUTTON_GPIO GPIOA
#define BUTTON_PIN GPIO_PIN_0
#define BUTTON_PRESSED_STATE GPIO_PIN_RESET
void EXTI0_IRQHandler(void)
{
HAL_GPIO_EXTI_IRQHandler(GPIO_PIN_0);
if (HAL_GPIO_ReadPin(BUTTON_GPIO, BUTTON_PIN) == BUTTON_PRESSED_STATE ) {
HAL_TIM_Base_Start_IT(&htim7);
__HAL_TIM_SET_COUNTER(&htim7, 0);
HAL_GPIO_WritePin(GPIOG, GPIO_PIN_13, GPIO_PIN_RESET);
} else {
HAL_GPIO_WritePin(GPIOG, GPIO_PIN_13, GPIO_PIN_SET);
HAL_TIM_Base_Stop_IT(&htim7);
}
}