【RISC-V MCU CH32V103测评】PWM测试
<p>CH32V103带有PWM输出功能，PWM输出功能在单机控制等应用中十分重要。但是实验结果让我很困惑。</p><p>参考例程C:\CH32V103EVT\EVT\EXAM\TIM\PWM_Output的内容，新建了一个项目TIM_PWM</p>
<p>主要初始化程序：</p>
<div aria-label="代码段 小部件" contenteditable="false" role="region" tabindex="-1">
<pre data-widget="codesnippet">
<code class="hljs language-cpp"><span class="hljs-comment">/*******************************************************************************
* Function Name: TIM1_PWMOut_Init
* Description : Initializes TIM1 PWM output.
* Input : arr: the period value.
* psc: the prescaler value.
* ccp: the pulse value.
* Return : None
*******************************************************************************/</span>
<span class="hljs-keyword">void</span> TIM1_PWMOut_Init( u16 arr, u16 psc, u16 ccp )
{
GPIO_InitTypeDef GPIO_InitStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
RCC_APB2PeriphClockCmd( RCC_APB2Periph_GPIOA | RCC_APB2Periph_TIM1, ENABLE );
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
GPIO_InitStructure.GPIO_Speed=GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_1;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
GPIO_InitStructure.GPIO_Speed=GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
TIM_TimeBaseInitStructure.TIM_Period = arr;
TIM_TimeBaseInitStructure.TIM_Prescaler = psc;
TIM_TimeBaseInitStructure.TIM_ClockDivision = TIM_CKD_DIV1;
TIM_TimeBaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit( TIM1, &TIM_TimeBaseInitStructure);
<span class="hljs-preprocessor">#if (PWM_MODE == PWM_MODE1)</span>
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
<span class="hljs-preprocessor">#elif (PWM_MODE == PWM_MODE2)</span>
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;
<span class="hljs-preprocessor">#endif</span>
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = ccp;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OC1Init( TIM1, &TIM_OCInitStructure );
TIM_CtrlPWMOutputs(TIM1, ENABLE );
TIM_OC1PreloadConfig( TIM1, TIM_OCPreload_Disable );
TIM_ARRPreloadConfig( TIM1, ENABLE );
TIM_Cmd( TIM1, ENABLE );
}
</code></pre>
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<p>程序中我加入了两只LED用来做程序指示，然后是PWM主角PA8，这些引脚都被设置为强上拉输出模式。</p>
<p>GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;<br />
GPIO_InitStructure.GPIO_Speed=GPIO_Speed_50MHz;</p>
<p>引脚的时钟是50MHZ,我不理解的是：<span style="color:#e74c3c;">我都把引脚设成PWM了或是什么其它的功能，你说这个时钟有什么用呢？</span></p>
<p>然后是定时器TIM1的设置，如果不知道为什么是TIM1请参考下图</p>
<p>TIM1在总线APB2上，PA8默认功能是TIM1_CH1(时钟TIM1的通道CH1)，程序中选定了引脚PA8就确定了初始化参数。</p>
<p>TIM1_PWMOut_Init(100, 48000-1, 50 );的三个参数，分别是</p>
<p> arr: the period value. //计数基数<br />
psc: the prescaler value. //分频系数<br />
ccp: the pulse value. //占空比</p>
<p>分频系数：48000-1，也就是1KHZ的计数基频，因为48MHZ的频率，每47999个脉冲计数翻转一次。</p>
<p>计数基数：这个是定时器的计数长度（计数基频的数量），注意：计数方向向上。</p>
<p>占空比：输出脉冲的计数时长。要小于计数基数的值，占空比 = ccp/psc</p>
<p>这是我测试的结果：</p>
<p> </p>
<p>看到默认参数的PWM的脉宽为50%的占空比的波形，频率为15HZ！</p>
<p>为什么呀？48M的主频，47999个脉冲计数时钟</p>
<p><span style="font-size:20px;"><span style="color:#e74c3c;">1K的基础时钟，100的计数值，1/1000*100 = 0.1s的周期,怎么是15HZ，有明白的同行给解释一下了</span></span></p>
<p> </p>
<p> </p>
<p> </p>
<p> </p>
<p>主频应该是配置成72MHz了</p>
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