Timer using STM32 Blue Pill

Implementing three popular methods of using timers (namely, Interrupt Mode, Polling Mode and DMA Mode).

Results:

• Green LED (onboard) is controlled by Interrupt Mode.
• Yellow LED (left) connected on Pin B10 and is controlled by Polling Mode.
• White LED (right) connected on Pin A11 and is controlled by DMA Mode.

1. Using Timers in Interrupt Mode:

• It sets up a free-running counter.
• Update Event (UEV) flag is set when the timer reaches the Period value.
• The TIM6_IRQHandler() ISR fires when the timer overflows, and the HAL_TIM_IRQHandler() is then called.
• Example [[Timers using STM32#^a8c9a6]]

2. Using Timers in Poll Mode:

The idea behind the polling mode is that the timer counter register (TIMx->CNT) is accessed continuously to check for a given value. A two common ways are:

1. checking if the timer current counter value is greater or equal than the given value.

...
while (1) {
	if(__HAL_TIM_GET_COUNTER(&htim2) >= 500){
		HAL_GPIO_TogglePin(LED2_GPIO_Port, LED2_Pin);
	}
...

2. checking against the UIF flag status.

...
while (1) {
if(__HAL_TIM_GET_FLAG(&tim) == TIM_FLAG_UPDATE) {
//Clear the IRQ flag otherwise we lose other events
__HAL_TIM_CLEAR_IT(htim, TIM_IT_UPDATE);
...

Note: The correct way is by using Interrupt Mode unless the timers runs very fast and interrupt (e.g. after every few microseconds) hinders the code execution.

3. Using Timers in DMA Mode:

This mode allows timers to trigger and control [[DMA]] transfers automatically, without CPU intervention.

1. First, the DMA Handle is initialization.

  hdma_tim2_up.Instance = DMA1_Channel2;
  hdma_tim2_up.Init.Direction = DMA_MEMORY_TO_PERIPH;
  hdma_tim2_up.Init.PeriphInc = DMA_PINC_DISABLE;
  hdma_tim2_up.Init.MemInc = DMA_MINC_ENABLE;
  hdma_tim2_up.Init.PeriphDataAlignment = DMA_PDATAALIGN_BYTE;
  hdma_tim2_up.Init.MemDataAlignment = DMA_MDATAALIGN_BYTE;
  hdma_tim2_up.Init.Mode = DMA_CIRCULAR;
  hdma_tim2_up.Init.Priority = DMA_PRIORITY_LOW;

2. A trigger event is first set for the DMA. For example, we can define Timer UP request (generated when timer is overflowed) as an trigger event.

   HAL_DMA_Init(&hdma_timx_up);

3. Then, the data (that is copied to the buffer of DMA) and the register (where the data is to be copied) are defined.

HAL_DMA_Start(&hdma_tim6_up, (uint32_t)data, (uint32_t)&GPIOA->ODR, 2);

where, 'hdma_tim6_up' is the trigger, 'data' is the address to data, 'GPIOA->ODR' is the register, and '2' is the length of the array.

4. Then, TIM Update DMA request is enabled.

__HAL_TIM_ENABLE_DMA(htim, TIM_DMA_UPDATE);