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Initial commit of STM32 test code.
author Daniel O'Connor <darius@dons.net.au>
date Mon, 03 Oct 2011 21:19:15 +1030
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1 <html>
2
3 <head>
4 <title>CMSIS Debug Support</title>
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72 </style>
73 </head>
74
75 <body>
76
77 <h1>CMSIS Debug Support</h1>
78
79 <hr>
80
81 <h2>Cortex-M3 ITM Debug Access</h2>
82 <p>
83 The Cortex-M3 incorporates the Instrumented Trace Macrocell (ITM) that provides together with
84 the Serial Viewer Output trace capabilities for the microcontroller system. The ITM has
85 32 communication channels which are able to transmit 32 / 16 / 8 bit values; two ITM
86 communication channels are used by CMSIS to output the following information:
87 </p>
88 <ul>
89 <li>ITM Channel 0: used for printf-style output via the debug interface.</li>
90 <li>ITM Channel 31: is reserved for RTOS kernel awareness debugging.</li>
91 </ul>
92
93 <h2>Debug IN / OUT functions</h2>
94 <p>CMSIS provides following debug functions:</p>
95 <ul>
96 <li>ITM_SendChar (uses ITM channel 0)</li>
97 <li>ITM_ReceiveChar (uses global variable)</li>
98 <li>ITM_CheckChar (uses global variable)</li>
99 </ul>
100
101 <h3>ITM_SendChar</h3>
102 <p>
103 <strong>ITM_SendChar</strong> is used to transmit a character over ITM channel 0 from
104 the microcontroller system to the debug system. <br>
105 Only a 8 bit value is transmitted.
106 </p>
107 <pre>
108 static __INLINE uint32_t ITM_SendChar (uint32_t ch)
109 {
110 /* check if debugger connected and ITM channel enabled for tracing */
111 if ((CoreDebug->DEMCR & CoreDebug_DEMCR_TRCENA) &amp;&amp;
112 (ITM-&gt;TCR & ITM_TCR_ITMENA) &amp;&amp;
113 (ITM-&gt;TER & (1UL &lt;&lt; 0)) )
114 {
115 while (ITM-&gt;PORT[0].u32 == 0);
116 ITM-&gt;PORT[0].u8 = (uint8_t)ch;
117 }
118 return (ch);
119 }</pre>
120
121 <h3>ITM_ReceiveChar</h3>
122 <p>
123 ITM communication channel is only capable for OUT direction. For IN direction
124 a globel variable is used. A simple mechansim detects if a character is received.
125 The project to test need to be build with debug information.
126 </p>
127
128 <p>
129 The globale variable <strong>ITM_RxBuffer</strong> is used to transmit a 8 bit value from debug system
130 to microcontroller system. <strong>ITM_RxBuffer</strong> is 32 bit wide to enshure a proper handshake.
131 </p>
132 <pre>
133 extern volatile int ITM_RxBuffer; /* variable to receive characters */
134 </pre>
135 <p>
136 A dedicated bit pattern is used to determin if <strong>ITM_RxBuffer</strong> is empty
137 or contains a valid value.
138 </p>
139 <pre>
140 #define ITM_RXBUFFER_EMPTY 0x5AA55AA5 /* value identifying ITM_RxBuffer is ready for next character */
141 </pre>
142 <p>
143 <strong>ITM_ReceiveChar</strong> is used to receive a 8 bit value from the debug system. The function is nonblocking.
144 It returns the received character or '-1' if no character was available.
145 </p>
146 <pre>
147 static __INLINE int ITM_ReceiveChar (void) {
148 int ch = -1; /* no character available */
149
150 if (ITM_RxBuffer != ITM_RXBUFFER_EMPTY) {
151 ch = ITM_RxBuffer;
152 ITM_RxBuffer = ITM_RXBUFFER_EMPTY; /* ready for next character */
153 }
154
155 return (ch);
156 }
157 </pre>
158
159 <h3>ITM_CheckChar</h3>
160 <p>
161 <strong>ITM_CheckChar</strong> is used to check if a character is received.
162 </p>
163 <pre>
164 static __INLINE int ITM_CheckChar (void) {
165
166 if (ITM_RxBuffer == ITM_RXBUFFER_EMPTY) {
167 return (0); /* no character available */
168 } else {
169 return (1); /* character available */
170 }
171 }</pre>
172
173
174 <h2>ITM Debug Support in uVision</h2>
175 <p>
176 uVision uses in a debug session the <strong>Debug (printf) Viewer</strong> window to
177 display the debug data.
178 </p>
179 <p>Direction microcontroller system -&gt; uVision:</p>
180 <ul>
181 <li>
182 Characters received via ITM communication channel 0 are written in a printf style
183 to <strong>Debug (printf) Viewer</strong> window.
184 </li>
185 </ul>
186
187 <p>Direction uVision -&gt; microcontroller system:</p>
188 <ul>
189 <li>Check if <strong>ITM_RxBuffer</strong> variable is available (only performed once).</li>
190 <li>Read character from <strong>Debug (printf) Viewer</strong> window.</li>
191 <li>If <strong>ITM_RxBuffer</strong> empty write character to <strong>ITM_RxBuffer</strong>.</li>
192 </ul>
193
194 <p class="Note">Note</p>
195 <ul>
196 <li><p>Current solution does not use a buffer machanism for trasmitting the characters.</p>
197 </li>
198 </ul>
199
200 <h2>RTX Kernel awareness in uVision</h2>
201 <p>
202 uVision / RTX are using a simple and efficient solution for RTX Kernel awareness.
203 No format overhead is necessary.<br>
204 uVsion debugger decodes the RTX events via the 32 / 16 / 8 bit ITM write access
205 to ITM communication channel 31.
206 </p>
207
208 <p>Following RTX events are traced:</p>
209 <ul>
210 <li>Task Create / Delete event
211 <ol>
212 <li>32 bit access. Task start address is transmitted</li>
213 <li>16 bit access. Task ID and Create/Delete flag are transmitted<br>
214 High byte holds Create/Delete flag, Low byte holds TASK ID.
215 </li>
216 </ol>
217 </li>
218 <li>Task switch event
219 <ol>
220 <li>8 bit access. Task ID of current task is transmitted</li>
221 </ol>
222 </li>
223 </ul>
224
225 <p class="Note">Note</p>
226 <ul>
227 <li><p>Other RTOS information could be retrieved via memory read access in a polling mode manner.</p>
228 </li>
229 </ul>
230
231
232 <p class="MsoNormal"><span lang="EN-GB">&nbsp;</span></p>
233
234 <hr>
235
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238 Visit our web site at <a href="http://www.keil.com">www.keil.com</a>.
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