一个定时器输出4路PWM异常问题记录

发布于 2024-03-21 20:01:50 浏览：373 订阅该版

[tocm]

# 问题描述

使用一个定时器同时输出4路PWM，频率不变的情况下改变占空比，改变的瞬间会导致频率改变。

代码：

```
	#define PWM_DEV_NAME_FRONT       "pwm2"  /* PWM设备名称 */

struct rt_device_pwm *pwm_dev;      /* PWM设 备 句 柄 */

/*motor PWM init*/
rt_err_t Motor_PWM_Init(void)
{
    rt_uint32_t period, pulse;
    period = 40000;    /* 周 期 为0.5ms， 单 位 为 纳 秒ns */
    pulse  = 0;         /* PWM脉 冲 宽 度 值， 单 位 为 纳秒ns */

pwm_dev = (struct rt_device_pwm *)rt_device_find(PWM_DEV_NAME_FRONT);
    if (pwm_dev == RT_NULL)
    {
        rt_kprintf("pwm sample run failed! can't find %s device!\n", PWM_DEV_NAME_FRONT);
        return RT_ERROR;
    }
    /* 设置PWM周期和脉冲宽度默认值 */
    rt_pwm_set(pwm_dev, 1, period, pulse);
    rt_pwm_set(pwm_dev, 2, period, pulse);
    rt_pwm_set(pwm_dev, 3, period, pulse);
    rt_pwm_set(pwm_dev, 4, period, pulse);
    /* 使能设备 */
    rt_pwm_enable(pwm_dev, 1);
    rt_pwm_enable(pwm_dev, 2);
    rt_pwm_enable(pwm_dev, 3);
    rt_pwm_enable(pwm_dev, 4);
    return RT_EOK;
}

int main(void)
{
    Motor_PWM_Init();

static rt_uint32_t motor_test = 400;
    for(; ; )
    {
        rt_pwm_set(pwm_dev, 1, 40000, motor_test);
        rt_pwm_set(pwm_dev, 2, 40000, motor_test);
        rt_pwm_set(pwm_dev, 3, 40000, motor_test);
        rt_pwm_set(pwm_dev, 4, 40000, motor_test);
        motor_test += 400;
        motor_test = motor_test > 20000 ? 400 : motor_test;
        rt_thread_mdelay(1);
    }

return 0;
}
```

逻辑分析仪波形图

![微信图片编辑_20240321195606.jpg](https://oss-club.rt-thread.org/uploads/20240321/b7ad42d9ec2156f2334a6633c0bc15fb.jpg.webp)

1. 异常波形的数量和开启几路PWM波形有关。在开启一路以上的PWM的时候，异常波形会随着增加。这张图片是开启4路PWM时的波形。
2. 如果使用不同的定时器单独输出一路PWM不会出现这种情况。