MM32F3273G8P火龙果开发板MindSDK开发教程21 - PWM的使用

MM32F3273G8P火龙果开发板MindSDK开发教程21 - PWM的使用

1、简述

开发版的LED灯连接PA1脚，而PA1可以映射TIM2_CH2，所以我们用通用定时器2的TIM2_CH2输出PWM到PA1脚，通过更改PWM的占空比，来改变LED的亮度。

2、LED灯的初始化

将PA1设定为GPIO_PinMode_AF_PushPull，并开启映射。

void GPIO_PA1_Config(void)
{
    /* gpio. */
    GPIO_Init_Type gpio_init;
    /* PA1 - TIM2_CH2_COMP. */
    gpio_init.Pins  = GPIO_PIN_1;
    gpio_init.PinMode  = GPIO_PinMode_AF_PushPull;
    gpio_init.Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOA, &gpio_init);
    GPIO_PinAFConf(GPIOA, gpio_init.Pins, GPIO_AF_1);
}

3、Tim2的初始化

假定输出1KHZ的pwm波形，tim2的时钟频率为120000000，设定tim2 的prescaler = 120 -1，那么tim2 color = 120000000/（120+1） = 1000000，即StepFreqHz=1000000 。也就是1s钟需要计数1000000次，而0.001s需要计数1000次，所以period = 1000 -1。
TIM_PutChannelValue(TIM2, TIM_CHN_2, 500);/* Change duty cycle. */ 500 即period的一半，占空比=500/1000=50%，250即占空比=25%。

void TIM2_Config(void)
{
    GPIO_PA1_Config();

    /* Set the counter counting step.  1000HZ*/
    TIM_Init_Type tim_init;
    tim_init.ClockFreqHz = 120000000;
    tim_init.StepFreqHz = 1000000;
    tim_init.Period = 1000 - 1u;
    tim_init.EnablePreloadPeriod = false;
    tim_init.PeriodMode = TIM_PeriodMode_Continuous;
    tim_init.CountMode = TIM_CountMode_Increasing;
    TIM_Init(TIM2, &tim_init);

    /* Set the PWM output channel. */
    TIM_OutputCompareConf_Type tim_outcomp_conf;
    tim_outcomp_conf.ChannelValue = 0u;
    tim_outcomp_conf.EnableFastOutput = false;
    tim_outcomp_conf.EnablePreLoadChannelValue = false; /* Disable preload, put data immediately. */
    tim_outcomp_conf.RefOutMode = TIM_OutputCompareRefOut_FallingEdgeOnMatch;
    tim_outcomp_conf.ClearRefOutOnExtTrigger = false;
    tim_outcomp_conf.PinPolarity = TIM_PinPolarity_Rising;
    TIM_EnableOutputCompare(TIM2, TIM_CHN_2, &tim_outcomp_conf);

    /* Start the output compare. */
    TIM_EnableOutputCompareSwitch(TIM2, true);
    TIM_PutChannelValue(TIM2, TIM_CHN_2, 500);/* Change duty cycle. */
    /* Start the counter. */
    TIM_Start(TIM2);
}

4、Letter Shell命令添加

pwn on 开启pwm
pwm off 关闭pwm
pwm freq xx (xx为1-1000的数值)。设定pwm的占空比

int set_pwm(int argc,char *argv[])
{
	if (argc == 2)
	{
		if (!strncmp(argv[1],"on",2))
		{
    		TIM_Start(TIM2);
			printf("PWM On\r\n");
		}
		else if(!strncmp(argv[1],"off",3))
		{
			TIM_Stop(TIM2);
			LED_Off();
			printf("PWM Off\r\n");
		}
		else
		{
			printf("error ,please use 'pwm freq xx(1-1000)' /pwm on /pwm off\r\n");
			return -1;
		}
		
	}
	else if (argc == 3)
	{
		if (!strncmp(argv[1],"freq",4))
		{
			uint16_t period = strtol(argv[2],NULL,10);
			if (period > 0 && period < 1000)
			{
				printf("Pwm duty cycle changed \r\n");
				TIM_Stop(TIM2);
				LED_Off();
				TIM_PutChannelValue(TIM2, TIM_CHN_2, period);/* Change duty cycle. */
				TIM_Start(TIM2);
			}
			else
			{
				printf("error ,please use 'pwm freq xx(1-1000)' /pwm on /pwm off\r\n");
				return -1;
			}

		}
		else
		{
			printf("error ,please use 'pwm freq xx(1-1000)' /pwm on /pwm off\r\n");
			return -1;
		}
	}
	else
	{
		printf("error ,please use 'pwm freq xx(1-1000)' /pwm on /pwm off\r\n");
		return -1;
	}

    return 0;
}

SHELL_EXPORT_CMD(SHELL_CMD_PERMISSION(0)|SHELL_CMD_TYPE(SHELL_TYPE_CMD_MAIN), pwm, set_pwm, set_pwm);

5、现象

输入pwm freq 200 以及pwm freq 800的波形图如下：

6、代码

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