TM4C123GXL_时钟配置

<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>TM4C123GXL_时钟配置</title>

    <link rel="stylesheet" href="https://stackedit.io/style.css">

<div class="stackedit__html">
<h1>TM4C的时钟源有四个</h1>

下面来看一下TM4C的时钟树

从时钟树上可以得到我们上面介绍的时候的一些信息，它的时钟源有四个，MOSC和PIOSC可以用来驱动PLL，PLL的输出为400MHz，然后可以进行分频作为系统时钟，每个时钟源都可以作为哪部分的时钟，以及如何分频，相关的寄存器都在时钟树上有标注，可以根据需要查询。

​ 下面讲一讲固件库对时钟的配置，先看一个示例

<span class="token comment">/ 时钟配置，2.5分频，80Mhz，系统时钟使用PLL，使用外部主时钟源，外部晶振为16MHz /</span>
<span class="token function">SysCtlClockSet</span><span class="token punctuation">(</span><span class="token constant">SYSCTL_SYSDIV_2_5</span> <span class="token operator">|</span> <span class="token constant">SYSCTL_USE_PLL</span> <span class="token operator">|</span> <span class="token constant">SYSCTL_OSC_MAIN</span> <span class="token operator">|</span> <span class="token constant">SYSCTL_XTAL_16MHZ</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

​ 这里有一点要注意TM4C123G的最大主频为80MHz，因此配置时钟的时候，若使用的PLL，最小分频数只能是2.5分频。

​ 固件库中配置适中需要用到这个函数

<span class="token keyword">void</span> <span class="token function">SysCtlClockSet</span><span class="token punctuation">(</span>uint32_t ui32Config<span class="token punctuation">)</span><span class="token punctuation">;</span>

​ 它包含在driverlib/sysctl.h中，这个函数的输入参数有四个部分，需要与在一起作为参数。四个部分分别是分频值，系统时钟来源是PLL还是OSC，使用的时钟源是什么，以及外部晶振的频率是什么。下面简单列举一下各部分的参数都是什么，然后详细的可以自己查看固件库的sysctl.h文件。

时钟分频

<span class="token constant">SYSCTL_SYSDIV_1</span>     <span class="token comment">// Processor clock is osc/pll /1</span>
<span class="token constant">SYSCTL_SYSDIV_2</span>     <span class="token comment">// Processor clock is osc/pll /2</span>
<span class="token constant">SYSCTL_SYSDIV_3</span>     <span class="token comment">// Processor clock is osc/pll /3</span>
<span class="token operator">...</span><span class="token operator">...</span><span class="token operator">...</span><span class="token punctuation">.</span>
<span class="token constant">SYSCTL_SYSDIV_64</span>    <span class="token comment">// Processor clock is osc/pll /64</span>
<span class="token constant">SYSCTL_SYSDIV_2_5</span>   <span class="token comment">// Processor clock is pll / 2.5</span>
<span class="token constant">SYSCTL_SYSDIV_3_5</span>   <span class="token comment">// Processor clock is pll / 3.5</span>
<span class="token operator">...</span><span class="token operator">...</span><span class="token operator">...</span><span class="token punctuation">.</span>
<span class="token constant">SYSCTL_SYSDIV_63_5</span>  <span class="token comment">// Processor clock is pll / 63.5</span>

2_5就是2.5分频的意思

系统时钟来源

<span class="token constant">SYSCTL_USE_PLL</span>  <span class="token comment">// System clock is the PLL clock</span>
<span class="token constant">SYSCTL_USE_OSC</span>  <span class="token comment">// System clock is the osc clock</span>

时钟源选择

<span class="token constant">SYSCTL_OSC_MAIN</span>  <span class="token comment">// Osc source is main osc</span>
<span class="token constant">SYSCTL_OSC_INT</span>   <span class="token comment">// Osc source is int. osc</span>
<span class="token constant">SYSCTL_OSC_INT4</span>  <span class="token comment">// Osc source is int. osc /4</span>
<span class="token constant">SYSCTL_OSC_INT30</span> <span class="token comment">// Osc source is int. 30 KHz</span>
<span class="token constant">SYSCTL_OSC_EXT32</span> <span class="token comment">// Osc source is ext. 32 KHz</span>

外部晶振大小选择

<span class="token constant">SYSCTL_XTAL_1MHZ</span>        <span class="token comment">// External crystal is 1MHz</span>
<span class="token constant">SYSCTL_XTAL_1_84MHZ</span>     <span class="token comment">// External crystal is 1.8432MHz</span>
<span class="token constant">SYSCTL_XTAL_2MHZ</span>        <span class="token comment">// External crystal is 2MHz</span>
<span class="token constant">SYSCTL_XTAL_2_45MHZ</span>     <span class="token comment">// External crystal is 2.4576MHz</span>
<span class="token constant">SYSCTL_XTAL_3_57MHZ</span>     <span class="token comment">// External crystal is 3.579545MHz</span>

​ 除了以上的这些参数，还有一些别的参数可作选择，可以查看手册根据需要选择，这里只给出常用的一些。

</div>