Using Tim2 inside interrupt handler for STM32F1 - embedded

Question

I am blinking LED using TIM2 General timer.
Code in main.c
HAL_TIM_Base_Start_IT(&htim2);
void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim){
if(htim->Instance==TIM2){
HAL_GPIO_TogglePin(GPIOB, LED_Pin);
}
}
When the button is clicked EXTI interrupt should be called to blink the led faster 20 times. However, LED stays on and stops blinking at all.
void EXTI0_IRQHandler(void)
{
HAL_GPIO_EXTI_IRQHandler(GPIO_PIN_0);
}
void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin){
if(GPIO_Pin == BT_Pin){
for(volatile int i=20; i>0; i--){
HAL_GPIO_TogglePin(GPIOB, LED_Pin);
HAL_Delay(100);
}
}
}
Could you please advice how can i adjust interrupt ISR for EXTI so it will use TIM2 as well with faster blinking.

Answer 1

HAL_GPIO_EXTI_Callback() runs in the interrupt context - it is not appropriate to flash the indicator there much less include a delay. No other code while run while in the interrupt, and HAL_Delay() is probably not interrupt safe in any case.
Instead, in the button handler, set a down-counter to be decremented in the timer handler, and in the timer handler set the reload depending on the down-counter being zero or not. Something like this:
[I have not included the HAL calls to do the TODO's above, because I'd have to look them up, but that is the outline.]
volatile unsigned fast_flash_count = 0 ;
void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
if(htim->Instance==TIM2)
{
HAL_GPIO_TogglePin(GPIOB, LED_Pin);
if( fast_flash_count > 0 )
{
fast_flash_count-- ;
// Set TIM2 reload to fast-flash period
TODO
}
else
{
// Set TIM2 reload to slow-flash period
TODO
}
}
}
void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin)
{
if(GPIO_Pin == BT_Pin)
{
fast_flash_count = 20 ;
// Set TIM2 counter to current reload value
// to force immediate interrupt
TODO
}
}