HAL library—Timer usage and PWM

Timing comparison with 51 microcontroller

Delay of 51 microcontroller (software timing):

//由stc软件生成的51延时代码
void Delay500ms() //@11.0592MHz
{
    
    
unsigned char i, j, k;
_nop_();
i = 4;
j = 129;
k = 119;
do
{
    
    
do
{
    
    
while (--k);
} while (--j);
} while (--i);
}

Disadvantages: imprecise, occupying CPU resources

Working principle of stm32 timer:

Use an accurate time base to implement timing functions through hardware. The core of the timer is the counter.

Timer classification:

• Basic timer (TIM6~TIM7)
• General timer (TIM2~TIM5)
• Advanced timers (TIM1 and TIM8)

STM32F103C8T6 timer resources:

General timer introduction:

1. 16-bit up, down, up/down autoload counter (TIMx_CNT).
2. 
   16-bit programmable (can be modified in real time) prescaler (TIMx_PSC), the division coefficient of the counter clock frequency is any value between 1 and 65535 .
3. 4 independent channels (TIMx_CH1~4), these channels can be used as:
   A. Input captureB
   . Output comparison
   C．PWM generation (edge ​​or center aligned mode)
   D. Single pulse mode output
4. The synchronization circuit of timers and timer interconnects (one timer can be used to control another timer) can be controlled using external signals (TIMx_ETR)
   .
5. Interrupt/DMA is generated when the following events occur:
   A. Update: counter overflows/underflows, counter initialization (via software or internal/external trigger)
   B. Trigger events (counter start, stop, initialization or counting triggered by internal/external)
   C. Input captureD
   . Output comparison
   E. Supports incremental (quadrature) encoder and Hall sensor circuits for positioning
   F. Trigger input as external clock or cycle-by-cycle current management

Timer counting mode:

Timer clock source:

The timer overflow time calculation formula is:

(PSC is the frequency division coefficient) (ARR is the reload value) (Tout is the output time (required)) (Tclk is the clock frequency)
Known: Tclk = 72MHZ.
For example, if you want to time 1000ms, then: PSC=7199, ARR=9999 ,Tclk=72M

#############################################################################

PWM resources

• Advanced timer (TIM1): 7 channels
• General timer (TIM2~TIM4): 4 channels each

PWM output mode:

• PWM mode 1: When counting up, once CNT < CCRx, the output is a valid level, otherwise it is an invalid level; when counting down, once
  CNT > CCRx, the output is an invalid level, otherwise it is a valid level.

• PWM mode 2: When counting up, the output is an invalid level once CNT < CCRx, otherwise it is a valid level; when counting down, the
  output is a valid level once CNT > CCRx, otherwise it is an invalid level.

PWM duty cycle: determined by the TIMx_CCRx register.

PWM configuration (Cube Max)

//启动tim2
HAL_TIM_Base_Start_IT(&htim2);
//配置占空比
//参数：句柄，通道，值
__HAL_TIM_SetCompare(&htim4, TIM_CHANNEL_3, pwmVal);

PWM breathing light experiment

int main()
{
    
    
// 定义变量
uint16_t pwmVal=0; //调整PWM占空比
uint8_t flag=1; //设置改变方向。1:占空比越来越大；0:占空比越来越小

// 使能 Timer4 第3通道 PWM 输出
HAL_TIM_PWM_Start(&htim4,TIM_CHANNEL_3);
// while循环实现呼吸灯效果
	while (1)
	{
    
    
		HAL_Delay(1);
		if (flag)
		pwmVal++;
		else
		pwmVal--;
		if (pwmVal > 500)
		flag = 0;
		if (pwmVal == 0)
		flag = 1;
		//修改比较值，修改占空比
		__HAL_TIM_SetCompare(&htim4, TIM_CHANNEL_3, pwmVal);
	}
}

Finish

If you have any questions, please feel free to raise them and make progress together.