[国民技术N32WB452测评] 二、PWM输出代码分析及呼吸灯实现

kit7828

[国民技术N32WB452测评] 二、PWM输出代码分析及呼吸灯实现 [复制链接]

 

国民技术N32WB452提供了很多的示例程序，其中涉及PWM输出的在TIM目录下，为定时器的案例之一。

1、PWM Output示例

示例程序路径

 示例代码的目录有个readme文件，说明了其功能

 收头没有示波器就没办法得到波形了

2、代码分析

具体的实现代码比较简单

首先是时钟RCC的开启及其使能

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void RCC_Configuration(void)
{
    /* TIM3 clock enable */
    RCC_EnableAPB1PeriphClk(RCC_APB1_PERIPH_TIM3, ENABLE);

    /* GPIOA and GPIOB clock enable */
    RCC_EnableAPB2PeriphClk(
        RCC_APB2_PERIPH_GPIOA | RCC_APB2_PERIPH_GPIOB | RCC_APB2_PERIPH_GPIOC | RCC_APB2_PERIPH_AFIO, ENABLE);
}

接下来是GPIO的设置

由于TIM3的通道CH1-CH4分别对应PA6、PA7、PB0和PB1，GPIO也只针对这4各管脚进行

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void GPIO_Configuration(void)
{
    GPIO_InitType GPIO_InitStructure;

    /* GPIOA Configuration:TIM3 Channel1, 2, 3 and 4 as alternate function push-pull */
    GPIO_InitStructure.Pin        = GPIO_PIN_6 | GPIO_PIN_7;
    GPIO_InitStructure.GPIO_Mode  = GPIO_Mode_AF_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

    GPIO_InitPeripheral(GPIOA, &GPIO_InitStructure);

    GPIO_InitStructure.Pin = GPIO_PIN_0 | GPIO_PIN_1;
    GPIO_InitPeripheral(GPIOB, &GPIO_InitStructure);
}

下面是定时器及其通道的设置，代码里做了比较详细的说明

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/* -----------------------------------------------------------------------
    TIM3 Configuration: generate 4 PWM signals with 4 different duty cycles:
    The TIM3CLK frequency is set to SystemCoreClock (Hz), to get TIM3 counter
    clock at 24 MHz the Prescaler is computed as following:
     - Prescaler = (TIM3CLK / TIM3 counter clock) - 1
    SystemCoreClock is set to 72 MHz for Low-density, Medium-density, High-density
    and Connectivity line devices and to 24 MHz for Low-Density Value line and
    Medium-Density Value line devices

    The TIM3 is running at 36 KHz: TIM3 Frequency = TIM3 counter clock/(AR + 1)
                                                  = 24 MHz / 666 = 36 KHz
    TIM3 Channel1 duty cycle = (TIM3_CCR1/ TIM3_ARR)* 100 = 50%
    TIM3 Channel2 duty cycle = (TIM3_CCR2/ TIM3_ARR)* 100 = 37.5%
    TIM3 Channel3 duty cycle = (TIM3_CCR3/ TIM3_ARR)* 100 = 25%
    TIM3 Channel4 duty cycle = (TIM3_CCR4/ TIM3_ARR)* 100 = 12.5%
    ----------------------------------------------------------------------- */
    /* Compute the prescaler value */
    PrescalerValue = (uint16_t)(SystemCoreClock / 24000000) - 1;
    /* Time base configuration */
    TIM_TimeBaseStructure.Period    = 665;
    TIM_TimeBaseStructure.Prescaler = PrescalerValue;
    TIM_TimeBaseStructure.ClkDiv    = 0;
    TIM_TimeBaseStructure.CntMode   = TIM_CNT_MODE_UP;

    TIM_InitTimeBase(TIM3, &TIM_TimeBaseStructure);

    /* PWM1 Mode configuration: Channel1 */
    TIM_OCInitStructure.OcMode      = TIM_OCMODE_PWM1;
    TIM_OCInitStructure.OutputState = TIM_OUTPUT_STATE_ENABLE;
    TIM_OCInitStructure.Pulse       = CCR1_Val;
    TIM_OCInitStructure.OcPolarity  = TIM_OC_POLARITY_HIGH;

    TIM_InitOc1(TIM3, &TIM_OCInitStructure);

    TIM_ConfigOc1Preload(TIM3, TIM_OC_PRE_LOAD_ENABLE);

    /* PWM1 Mode configuration: Channel2 */
    TIM_OCInitStructure.OutputState = TIM_OUTPUT_STATE_ENABLE;
    TIM_OCInitStructure.Pulse       = CCR2_Val;

    TIM_InitOc2(TIM3, &TIM_OCInitStructure);

    TIM_ConfigOc2Preload(TIM3, TIM_OC_PRE_LOAD_ENABLE);

    /* PWM1 Mode configuration: Channel3 */
    TIM_OCInitStructure.OutputState = TIM_OUTPUT_STATE_ENABLE;
    TIM_OCInitStructure.Pulse       = CCR3_Val;

    TIM_InitOc3(TIM3, &TIM_OCInitStructure);

    TIM_ConfigOc3Preload(TIM3, TIM_OC_PRE_LOAD_ENABLE);

    /* PWM1 Mode configuration: Channel4 */
    TIM_OCInitStructure.OutputState = TIM_OUTPUT_STATE_ENABLE;
    TIM_OCInitStructure.Pulse       = CCR4_Val;

    TIM_InitOc4(TIM3, &TIM_OCInitStructure);

    TIM_ConfigOc4Preload(TIM3, TIM_OC_PRE_LOAD_ENABLE);

    TIM_ConfigArPreload(TIM3, ENABLE);

    /* TIM3 enable counter */
    TIM_Enable(TIM3, ENABLE);

通用定时器TIM3以24MHz的工作进行计数，其中计数周期设置为666，PWM的4个通道分别为这个计数周期的50%、37.5%、25%以及12.5%；

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uint16_t CCR1_Val       = 333;
uint16_t CCR2_Val       = 249;
uint16_t CCR3_Val       = 166;
uint16_t CCR4_Val       = 83;

设置完成后就由定时器TIM3硬件输出PWM信号了

3、呼吸灯实现

在这个demo案例中，稍微加点变化，就能实现呼吸灯效果了

定义了两个变量，一个为递增及递减的方向u8 dir，一个为记录输出比较器的参考值u16 led0pwmval=0；

在main主循环中增加以下代码

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while (1)
    {
		if(dir)led0pwmval++;                            //dir==1 led0pwmval递增
		else led0pwmval--;                              //dir==0 led0pwmval递减
		if(led0pwmval>660)dir=0;                        //led0pwmval到达660后，方向为递减		
		if(led0pwmval==0)dir=1;                        	//led0pwmval递减到0后，方向改为递增
		TIM3->CCDAT4 = led0pwmval;						//CH4 做呼吸灯
		Delay(0x01FFFF);								//约4ms * 600 = 2.4s  一次呼吸 5 s
    }

用通道4实现呼吸灯的效果

播放器加载失败: 未检测到Flash Player，请到安装

PWM呼吸灯

Keil的开发环境相对比较熟悉，整起来还是蛮快的。

秦天qintian0303

工作中使用的开发环境是keil多还是IAR多

freebsder

秦天qintian0303 发表于 2022-7-20 08:37 工作中使用的开发环境是keil多还是IAR多

国内keil多。外面差不多一样多。

kit7828

秦天qintian0303 发表于 2022-7-20 08:37 工作中使用的开发环境是keil多还是IAR多

很少用IAR，基本都是Keil

秦天qintian0303

kit7828 发表于 2022-7-21 13:38 很少用IAR，基本都是Keil

这个就和工作习惯相关了，真是开始决定结尾，基本都不愿意改了