1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/xhtml;charset=UTF-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=9"/>
<title>System and Clock Configuration</title>
<title>CMSIS-Core (Cortex-M): System and Clock Configuration</title>
<link href="tabs.css" rel="stylesheet" type="text/css"/>
<link href="cmsis.css" rel="stylesheet" type="text/css" />
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript" src="dynsections.js"></script>
<script type="text/javascript" src="printComponentTabs.js"></script>
<link href="navtree.css" rel="stylesheet" type="text/css"/>
<script type="text/javascript" src="resize.js"></script>
<script type="text/javascript" src="navtree.js"></script>
<script type="text/javascript">
$(document).ready(initResizable);
$(window).load(resizeHeight);
</script>
<link href="search/search.css" rel="stylesheet" type="text/css"/>
<script type="text/javascript" src="search/search.js"></script>
<script type="text/javascript">
$(document).ready(function() { searchBox.OnSelectItem(0); });
</script>
</head>
<body>
<div id="top"><!-- do not remove this div, it is closed by doxygen! -->
<div id="titlearea">
<table cellspacing="0" cellpadding="0">
<tbody>
<tr style="height: 46px;">
<td id="projectlogo"><img alt="Logo" src="CMSIS_Logo_Final.png"/></td>
<td style="padding-left: 0.5em;">
<div id="projectname">CMSIS-Core (Cortex-M)
 <span id="projectnumber">Version 5.1.2</span>
</div>
<div id="projectbrief">CMSIS-Core support for Cortex-M processor-based devices</div>
</td>
</tr>
</tbody>
</table>
</div>
<!-- end header part -->
<div id="CMSISnav" class="tabs1">
<ul class="tablist">
<script type="text/javascript">
<!--
writeComponentTabs.call(this);
//-->
</script>
</ul>
</div>
<!-- Generated by Doxygen 1.8.6 -->
<script type="text/javascript">
var searchBox = new SearchBox("searchBox", "search",false,'Search');
</script>
<div id="navrow1" class="tabs">
<ul class="tablist">
<li><a href="index.html"><span>Main Page</span></a></li>
<li><a href="pages.html"><span>Usage and Description</span></a></li>
<li><a href="modules.html"><span>Reference</span></a></li>
<li>
<div id="MSearchBox" class="MSearchBoxInactive">
<span class="left">
<img id="MSearchSelect" src="search/mag_sel.png"
onmouseover="return searchBox.OnSearchSelectShow()"
onmouseout="return searchBox.OnSearchSelectHide()"
alt=""/>
<input type="text" id="MSearchField" value="Search" accesskey="S"
onfocus="searchBox.OnSearchFieldFocus(true)"
onblur="searchBox.OnSearchFieldFocus(false)"
onkeyup="searchBox.OnSearchFieldChange(event)"/>
</span><span class="right">
<a id="MSearchClose" href="javascript:searchBox.CloseResultsWindow()"><img id="MSearchCloseImg" border="0" src="search/close.png" alt=""/></a>
</span>
</div>
</li>
</ul>
</div>
</div><!-- top -->
<div id="side-nav" class="ui-resizable side-nav-resizable">
<div id="nav-tree">
<div id="nav-tree-contents">
<div id="nav-sync" class="sync"></div>
</div>
</div>
<div id="splitbar" style="-moz-user-select:none;"
class="ui-resizable-handle">
</div>
</div>
<script type="text/javascript">
$(document).ready(function(){initNavTree('group__system__init__gr.html','');});
</script>
<div id="doc-content">
<!-- window showing the filter options -->
<div id="MSearchSelectWindow"
onmouseover="return searchBox.OnSearchSelectShow()"
onmouseout="return searchBox.OnSearchSelectHide()"
onkeydown="return searchBox.OnSearchSelectKey(event)">
<a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(0)"><span class="SelectionMark"> </span>All</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(1)"><span class="SelectionMark"> </span>Data Structures</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(2)"><span class="SelectionMark"> </span>Files</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(3)"><span class="SelectionMark"> </span>Functions</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(4)"><span class="SelectionMark"> </span>Variables</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(5)"><span class="SelectionMark"> </span>Enumerations</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(6)"><span class="SelectionMark"> </span>Enumerator</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(7)"><span class="SelectionMark"> </span>Groups</a><a class="SelectItem" href="javascript:void(0)" onclick="searchBox.OnSelectItem(8)"><span class="SelectionMark"> </span>Pages</a></div>
<!-- iframe showing the search results (closed by default) -->
<div id="MSearchResultsWindow">
<iframe src="javascript:void(0)" frameborder="0"
name="MSearchResults" id="MSearchResults">
</iframe>
</div>
<div class="header">
<div class="summary">
<a href="#func-members">Functions</a> |
<a href="#var-members">Variables</a> </div>
<div class="headertitle">
<div class="title">System and Clock Configuration</div> </div>
</div><!--header-->
<div class="contents">
<p>Functions for system and clock setup available in system_<em>device</em>.c.
<a href="#details">More...</a></p>
<table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="func-members"></a>
Functions</h2></td></tr>
<tr class="memitem:ga93f514700ccf00d08dbdcff7f1224eb2"><td class="memItemLeft" align="right" valign="top">void </td><td class="memItemRight" valign="bottom"><a class="el" href="group__system__init__gr.html#ga93f514700ccf00d08dbdcff7f1224eb2">SystemInit</a> (void)</td></tr>
<tr class="memdesc:ga93f514700ccf00d08dbdcff7f1224eb2"><td class="mdescLeft"> </td><td class="mdescRight">Function to Initialize the system. <a href="#ga93f514700ccf00d08dbdcff7f1224eb2">More...</a><br/></td></tr>
<tr class="separator:ga93f514700ccf00d08dbdcff7f1224eb2"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:gae0c36a9591fe6e9c45ecb21a794f0f0f"><td class="memItemLeft" align="right" valign="top">void </td><td class="memItemRight" valign="bottom"><a class="el" href="group__system__init__gr.html#gae0c36a9591fe6e9c45ecb21a794f0f0f">SystemCoreClockUpdate</a> (void)</td></tr>
<tr class="memdesc:gae0c36a9591fe6e9c45ecb21a794f0f0f"><td class="mdescLeft"> </td><td class="mdescRight">Function to update the variable <a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a>. <a href="#gae0c36a9591fe6e9c45ecb21a794f0f0f">More...</a><br/></td></tr>
<tr class="separator:gae0c36a9591fe6e9c45ecb21a794f0f0f"><td class="memSeparator" colspan="2"> </td></tr>
</table><table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="var-members"></a>
Variables</h2></td></tr>
<tr class="memitem:gaa3cd3e43291e81e795d642b79b6088e6"><td class="memItemLeft" align="right" valign="top">uint32_t </td><td class="memItemRight" valign="bottom"><a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a></td></tr>
<tr class="memdesc:gaa3cd3e43291e81e795d642b79b6088e6"><td class="mdescLeft"> </td><td class="mdescRight">Variable to hold the system core clock value. <a href="#gaa3cd3e43291e81e795d642b79b6088e6">More...</a><br/></td></tr>
<tr class="separator:gaa3cd3e43291e81e795d642b79b6088e6"><td class="memSeparator" colspan="2"> </td></tr>
</table>
<a name="details" id="details"></a><h2 class="groupheader">Description</h2>
<p>Arm provides a template file <b>system_<em>device</em>.c</b> that must be adapted by the silicon vendor to match their actual device. As a <b>minimum requirement</b>, this file must provide:</p>
<ul>
<li>A device-specific system configuration function, <a class="el" href="group__system__init__gr.html#ga93f514700ccf00d08dbdcff7f1224eb2">SystemInit()</a>.</li>
<li>A global variable that contains the system frequency, <a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a>.</li>
</ul>
<p>The file configures the device and, typically, initializes the oscillator (PLL) that is part of the microcontroller device. This file might export other functions or variables that provide a more flexible configuration of the microcontroller system.</p>
<dl class="section note"><dt>Note</dt><dd>Please pay special attention to the static variable <code>SystemCoreClock</code>. This variable might be used throughout the whole system initialization and runtime to calculate frequency/time related values. Thus one must assure that the variable always reflects the actual system clock speed. Be aware that a value stored to <code>SystemCoreClock</code> during low level initializaton (i.e. <code><a class="el" href="group__system__init__gr.html#ga93f514700ccf00d08dbdcff7f1224eb2" title="Function to Initialize the system. ">SystemInit()</a></code>) might get overwritten by C libray startup code. Thus its highly recommended to call <a class="el" href="group__system__init__gr.html#gae0c36a9591fe6e9c45ecb21a794f0f0f">SystemCoreClockUpdate</a> at the beginning of the user <code>main()</code> routine.</dd></dl>
<h1><a class="anchor" id="system_init_code_ex_sec"></a>
Code Example</h1>
<p>The code below shows the usage of the variable <a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a> and the functions <a class="el" href="group__system__init__gr.html#ga93f514700ccf00d08dbdcff7f1224eb2" title="Function to Initialize the system. ">SystemInit()</a> and <a class="el" href="group__system__init__gr.html#gae0c36a9591fe6e9c45ecb21a794f0f0f" title="Function to update the variable SystemCoreClock. ">SystemCoreClockUpdate()</a> with an LPC1700.</p>
<div class="fragment"><div class="line"><span class="preprocessor">#include "LPC17xx.h"</span></div>
<div class="line"></div>
<div class="line">uint32_t coreClock_1 = 0; <span class="comment">/* Variables to store core clock values */</span></div>
<div class="line">uint32_t coreClock_2 = 0;</div>
<div class="line"></div>
<div class="line"></div>
<div class="line"><span class="keywordtype">int</span> main (<span class="keywordtype">void</span>) {</div>
<div class="line"></div>
<div class="line"> coreClock_1 = <a class="code" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a>; <span class="comment">/* Store value of predefined SystemCoreClock */</span></div>
<div class="line"></div>
<div class="line"> <a class="code" href="group__system__init__gr.html#gae0c36a9591fe6e9c45ecb21a794f0f0f">SystemCoreClockUpdate</a>(); <span class="comment">/* Update SystemCoreClock according to register settings */</span></div>
<div class="line"></div>
<div class="line"> coreClock_2 = <a class="code" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a>; <span class="comment">/* Store value of calculated SystemCoreClock */</span></div>
<div class="line"></div>
<div class="line"> <span class="keywordflow">if</span> (coreClock_2 != coreClock_1) { <span class="comment">/* Without changing the clock setting both core clock values should be the same */</span> </div>
<div class="line"> <span class="comment">// Error Handling</span></div>
<div class="line"> }</div>
<div class="line"></div>
<div class="line"> <span class="keywordflow">while</span>(1);</div>
<div class="line">}</div>
</div><!-- fragment --> <h2 class="groupheader">Function Documentation</h2>
<a class="anchor" id="gae0c36a9591fe6e9c45ecb21a794f0f0f"></a>
<div class="memitem">
<div class="memproto">
<table class="memname">
<tr>
<td class="memname">void SystemCoreClockUpdate </td>
<td>(</td>
<td class="paramtype">void </td>
<td class="paramname"></td><td>)</td>
<td></td>
</tr>
</table>
</div><div class="memdoc">
<p>Updates the variable <a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a> and must be called whenever the core clock is changed during program execution. The function evaluates the clock register settings and calculates the current core clock. </p>
</div>
</div>
<a class="anchor" id="ga93f514700ccf00d08dbdcff7f1224eb2"></a>
<div class="memitem">
<div class="memproto">
<table class="memname">
<tr>
<td class="memname">void SystemInit </td>
<td>(</td>
<td class="paramtype">void </td>
<td class="paramname"></td><td>)</td>
<td></td>
</tr>
</table>
</div><div class="memdoc">
<p>Initializes the microcontroller system. Typically, this function configures the oscillator (PLL) that is part of the microcontroller device. For systems with a variable clock speed, it updates the variable <a class="el" href="group__system__init__gr.html#gaa3cd3e43291e81e795d642b79b6088e6">SystemCoreClock</a>. SystemInit is called from the file <b>startup<em>_device</em></b>. </p>
</div>
</div>
<h2 class="groupheader">Variable Documentation</h2>
<a class="anchor" id="gaa3cd3e43291e81e795d642b79b6088e6"></a>
<div class="memitem">
<div class="memproto">
<table class="memname">
<tr>
<td class="memname">uint32_t SystemCoreClock</td>
</tr>
</table>
</div><div class="memdoc">
<p>Holds the system core clock, which is the system clock frequency supplied to the SysTick timer and the processor core clock. This variable can be used by debuggers to query the frequency of the debug timer or to configure the trace clock speed.</p>
<dl class="section attention"><dt>Attention</dt><dd>Compilers must be configured to avoid removing this variable in case the application program is not using it. Debugging systems require the variable to be physically present in memory so that it can be examined to configure the debugger. </dd></dl>
</div>
</div>
</div><!-- contents -->
</div><!-- doc-content -->
<!-- start footer part -->
<div id="nav-path" class="navpath"><!-- id is needed for treeview function! -->
<ul>
<li class="footer">Generated on Wed Aug 1 2018 17:12:08 for CMSIS-Core (Cortex-M) by Arm Ltd. All rights reserved.
<!--
<a href="http://www.doxygen.org/index.html">
<img class="footer" src="doxygen.png" alt="doxygen"/></a> 1.8.6
-->
</li>
</ul>
</div>
</body>
</html>
|
