Error setting up timer HAL PeriodElapsed Callback STM32F334R8T
You should add the type of htim in the function declaration which is missing in:

void HAL_TIM_PeriodElapsedCallback(&amp;htim3)
{
  HAL_GPIO_TogglePin(N_CS_GPIO_Port, N_CS_Pin);
}


By adding it you will get:

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
  HAL_GPIO_TogglePin(N_CS_GPIO_Port, N_CS_Pin);
}


To check if the function is called for timer 3, check for the correct timer:

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
   if (htim == &amp;htim3)
   {
      HAL_GPIO_TogglePin(N_CS_GPIO_Port, N_CS_Pin);
   }
}


(I do not have a compiler at hand, so I cannot check the code).