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STM32复位和系统时钟.html
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<h1>STM32复位和系统时钟</h1>
<h4>2011-10-17，整理于2014-09-25 / xiahouzuoxin</h4>
<h4>Tags: ARM</h4>
转载请注明出处: <a href="http://xiahouzuoxin.github.io/notes/">http://xiahouzuoxin.github.io/notes/</a>
<!---title:STM32复位和系统时钟-->
<!---keywords:ARM-->
<!---date:2011-10-17，整理于2014-09-25-->
<p>这是一篇旧文，早在上大二的时候，在地下室（当时实验室在防空地下室）顺手在word上写的，当时STM32正刚刚开始蓬勃发展，如今时隔3年，整理到这里！</p>
<p>系统复位后，首先使用内部RC时钟源，由于内部时钟精度不高且不能倍频到较高频率，所以实际应用中一般使用外接晶振（8M）,下面是建立系统时钟的步骤：</p>
<ol style="list-style-type: decimal">
<li>将所有RCC外设寄存器重设为默认值</li>
<li>启用外部高速晶振</li>
<li>等待，直到外部晶振稳定</li>
<li>设置欲取址缓存使能和代码延时值</li>
<li>设置AHB时钟(HCLK)=系统时钟</li>
<li>设置高速APB2时钟（PCLK2）为系统时钟</li>
<li>设置低速APB1时钟（PCLK1）为系统时钟1/2，最高36MHz</li>
<li>设置PLL时钟源及倍频系数，使能PLL。PLL最高72MHz</li>
<li>等待PLL初始化成功</li>
<li>设置PLL为系统时钟源</li>
<li>等待PLL成功作为系统时钟源</li>
</ol>
<pre class="sourceCode c"><code class="sourceCode c"><span class="co">/*******************************************************************/</span>
<span class="co">/* function : Sysclk configuration</span>
<span class="co">/* author : 夏侯佐鑫</span>
<span class="co">/* data : 2011-10-17</span>
<span class="co">/*******************************************************************/</span>
<span class="dt">void</span> SysclkInit(<span class="dt">void</span>)
{
ErrorStatus HSEStartUpStatus;
<span class="co">//重设默认值</span>
RCC_DeInit();
<span class="co">//HSE</span>
RCC_HSEConfig(RCC_HES_ON);
<span class="co">//等待HSE稳定</span>
HSEStratUpStatus = RCC_WaitForHSEStartUp();
<span class="kw">if</span>(HSEStratUpStatus == SUCCESS)
{
<span class="co">//预取址缓存使能</span>
FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);
<span class="co">//设置代码延时值,2延时周期</span>
FLASH_SetLatency(FLSAH_Latency_2);
<span class="co">//AHB</span>
RCC_HCLKConfig(RCC_SYSCLK_Div1);
<span class="co">//APB2</span>
RCC_PCLK2Config(RCC_SYSCLK_Div1);
<span class="co">//APB1</span>
RCC_PCLK1Config(RCC_SYSCLK_Div2);
<span class="co">//PLLCLK = 8MHz * 9</span>
RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_9);
<span class="co">//Enable PLL</span>
RCC_PLLCmd(ENABLE);
<span class="co">//Wait PLL Init successed</span>
<span class="kw">while</span>(RESET == RCC_GetFlagStatus(RCC_FLAG_PLLRDY));
<span class="co">//SYSCLK = PLL clk</span>
RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);
<span class="co">//Wait PLL be SYSCLK</span>
<span class="kw">while</span>(RCC_GetSYSCLKSource() != <span class="bn">0x08</span>);
}
}</code></pre>
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