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。
在这里插入图片描述

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);