简介
以stm32f103rct6为例,下面说明如何使用通用定时器实现pwm输出
详细
stm32的定时器有多种类型,有RTC、基本定时器、通用定时器、高级定时器。下面我们选择通用定时器来实现pwm输出功能。
利用比较功能输出pwm
这里我选择TIM2定时器。
第一步:选择哪几个引脚输出pwm信号,这里我选择PA1、PA2,如下图:
第二步:使能外设时钟;使能GPIO的时钟,使能TIM2的时钟。
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2,ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE);
第三步:初始化GPIO功能(配置工作模式、io引脚、IO响应速度)
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_1;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_2MHz;
GPIO_Init(GPIOA, &GPIO_InitStruct);
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_2;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_2MHz;
GPIO_Init(GPIOA, &GPIO_InitStruct);
第四步:初始化timer(配置时钟分频、计数方式、自动重装值、预分频值)
TIM_TimeBaseInitTypeStruct.TIM_ClockDivision = TIM_CKD_DIV1;
TIM_TimeBaseInitTypeStruct.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInitTypeStruct.TIM_Period = arr;
TIM_TimeBaseInitTypeStruct.TIM_Prescaler = psc;
TIM_TimeBaseInit(TIM2, &TIM_TimeBaseInitTypeStruct);
第五步:初始化OC(OUTPUT COMPARE)(配置输出比较的模式、输出是否使能、输出的极性、比较值)
TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStruct.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OCInitStruct.TIM_Pulse = s_timer2_duty;
TIM_OC2Init(TIM2, &TIM_OCInitStruct);
TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM2;
TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStruct.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OCInitStruct.TIM_Pulse = s_timer2_duty;
TIM_OC3Init(TIM2, &TIM_OCInitStruct);
第六步:配置定时器的中断
TIM_ITConfig(TIM2,TIM_IT_Update|TIM_IT_CC2|TIM_IT_CC3,ENABLE);
第七步:配置MVIC 中断优先级,并使能irq通道
NVIC_InitTypeStruct.NVIC_IRQChannel = TIM2_IRQn;
NVIC_InitTypeStruct.NVIC_IRQChannelCmd = ENABLE;
NVIC_InitTypeStruct.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitTypeStruct.NVIC_IRQChannelSubPriority = 0;
NVIC_Init(&NVIC_InitTypeStruct);
最后一步,使能定时器
TIM_Cmd(TIM2,ENABLE);
演示效果如下:
使用软件仿真,利用逻辑分析仪观察波形,发现输出了两个互补pwm信号,占空比都是50%。
利用输入捕获功能测量pwm周期
对于输入捕获功能,我们可以按照以下步骤进行配置:
1、使能定时器及端口时钟,并设置引脚复用器映射和引脚模式等
2、初始化定时器参数,包含自动重装值,分频系数,计数方式等
3、设置通用定时器的输入捕获参数,开启输入捕获功能
4、开启捕获和定时器溢出(更新)中断
5、设置定时器中断优先级,使能定时器中断通道
6、编写定时器中断服务函数
7、使能定时器
以stm32f103rct6为例,这里我选择TIM3定时器的CH1做输入捕获,对应的引脚如下图:
核心代码如下:
第一步:使能定时器、gpio的时钟;初始化gpio
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE);
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_6;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_IN_FLOATING;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_2MHz;
GPIO_Init(GPIOA, &GPIO_InitStruct);
第二步:初始化定时器
TIM_ARRPreloadConfig(TIM3, ENABLE);
TIM_TimeBaseInitTypeStruct.TIM_ClockDivision = TIM_CKD_DIV1;
TIM_TimeBaseInitTypeStruct.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInitTypeStruct.TIM_Period = arr;
TIM_TimeBaseInitTypeStruct.TIM_Prescaler = psc;
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseInitTypeStruct);
第三步:设置捕获参数
TIM_ICInitStruct.TIM_Channel = TIM_Channel_1;
TIM_ICInitStruct.TIM_ICFilter = 0xf;
TIM_ICInitStruct.TIM_ICPolarity = TIM_ICPolarity_Rising;
TIM_ICInitStruct.TIM_ICPrescaler = TIM_ICPSC_DIV1;
TIM_ICInitStruct.TIM_ICSelection = TIM_ICSelection_DirectTI;
TIM_ICInit(TIM3, &TIM_ICInitStruct);
第四步:开启捕获和定时器溢出(更新)中断
TIM_ITConfig(TIM3,TIM_IT_Update|TIM_IT_CC1,ENABLE);
第五步:设置定时器中断优先级,使能定时器中断通道
NVIC_InitTypeStruct.NVIC_IRQChannel = TIM3_IRQn;
NVIC_InitTypeStruct.NVIC_IRQChannelCmd = ENABLE;
NVIC_InitTypeStruct.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitTypeStruct.NVIC_IRQChannelSubPriority = 0;
NVIC_Init(&NVIC_InitTypeStruct);
第六步:编写定时器中断服务函数
void TIM3_IRQHandler(void)
{
if(TIM_GetITStatus(TIM3,TIM_IT_Update)==SET)
{
if(s_tim3_IC_edge == 1)
{
s_tim3_exceed++;
}
TIM_ClearITPendingBit(TIM3,TIM_IT_Update);
}
if(TIM_GetITStatus(TIM3,TIM_IT_CC1)==SET)
{
TIM_Cmd(TIM3, DISABLE);
s_tim3_IC_edge++;
if(s_tim3_IC_edge == 1)
{
TIM_Cmd(TIM3, DISABLE);
TIM_SetCounter(TIM3, 0);
s_tim3_exceed = 0;
TIM_Cmd(TIM3, ENABLE);
}
else
{
TIM_Cmd(TIM3, DISABLE);
s_tim3_IC_val = TIM_GetCapture1(TIM3);
s_tim3_IC_edge = 0;
}
TIM_ClearITPendingBit(TIM3,TIM_IT_CC1);
}
}
第七步:使能定时器
TIM_Cmd(TIM3, ENABLE);
主任务负责读取pwm周期并重启定时器(这里通过RTOS周期执行任务实现)
tim.c
volatile uint16_t s_tim3_exceed = 0;
volatile uint8_t s_tim3_IC_edge = 0;
volatile uint16_t s_tim3_IC_val = 0;
main.c
void vTask1( void *pvParameters )
{
volatile int i = 0, j = 0;
portTickType xLastWakeTime;
xLastWakeTime = xTaskGetTickCount();
for( ;; )
{
uint16_t pwm_period;
pwm_period = timer_get_pwm_period();
TimerStart(timer3);
printf("pwm period is %hu ms\n", pwm_period);
vTaskDelayUntil(&xLastWakeTime, 1000 / portTICK_RATE_MS);
}
}
读取pwm周期的函数如下:
#define TIM3_ARR 2000
#define TIM3_TIME_BASE (72000000/36000)
#define SECONDS_TO_MICROSECONDS 1000000
uint16_t timer_get_pwm_period(void)
{
uint16_t ret;
ret = (s_tim3_IC_val + s_tim3_exceed*TIM3_ARR)*(SECONDS_TO_MICROSECONDS/TIM3_TIME_BASE);
ret = ret/1000;
return ret;
}
目前没有硬件环境,后面有时间再补充实测结果。
总结
后面有时间再慢慢添加对timer的其他功能的理解。
附录
通用定时器模块框图:
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