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+<html>
+
+<head>
+<title>CMSIS Debug Support</title>
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+<body>
+
+<h1>CMSIS Debug Support</h1>
+
+<hr>
+
+<h2>Cortex-M3 ITM Debug Access</h2>
+<p>
+ The Cortex-M3 incorporates the Instrumented Trace Macrocell (ITM) that provides together with
+ the Serial Viewer Output trace capabilities for the microcontroller system. The ITM has
+ 32 communication channels which are able to transmit 32 / 16 / 8 bit values; two ITM
+ communication channels are used by CMSIS to output the following information:
+</p>
+<ul>
+ <li>ITM Channel 0: used for printf-style output via the debug interface.</li>
+ <li>ITM Channel 31: is reserved for RTOS kernel awareness debugging.</li>
+</ul>
+
+<h2>Debug IN / OUT functions</h2>
+<p>CMSIS provides following debug functions:</p>
+<ul>
+ <li>ITM_SendChar (uses ITM channel 0)</li>
+ <li>ITM_ReceiveChar (uses global variable)</li>
+ <li>ITM_CheckChar (uses global variable)</li>
+</ul>
+
+<h3>ITM_SendChar</h3>
+<p>
+ <strong>ITM_SendChar</strong> is used to transmit a character over ITM channel 0 from
+ the microcontroller system to the debug system. <br>
+ Only a 8 bit value is transmitted.
+</p>
+<pre>
+static __INLINE uint32_t ITM_SendChar (uint32_t ch)
+{
+ /* check if debugger connected and ITM channel enabled for tracing */
+ if ((CoreDebug->DEMCR & CoreDebug_DEMCR_TRCENA) &amp;&amp;
+ (ITM-&gt;TCR & ITM_TCR_ITMENA) &amp;&amp;
+ (ITM-&gt;TER & (1UL &lt;&lt; 0)) )
+ {
+ while (ITM-&gt;PORT[0].u32 == 0);
+ ITM-&gt;PORT[0].u8 = (uint8_t)ch;
+ }
+ return (ch);
+}</pre>
+
+<h3>ITM_ReceiveChar</h3>
+<p>
+ ITM communication channel is only capable for OUT direction. For IN direction
+ a globel variable is used. A simple mechansim detects if a character is received.
+ The project to test need to be build with debug information.
+</p>
+
+<p>
+ The globale variable <strong>ITM_RxBuffer</strong> is used to transmit a 8 bit value from debug system
+ to microcontroller system. <strong>ITM_RxBuffer</strong> is 32 bit wide to enshure a proper handshake.
+</p>
+<pre>
+extern volatile int ITM_RxBuffer; /* variable to receive characters */
+</pre>
+<p>
+ A dedicated bit pattern is used to determin if <strong>ITM_RxBuffer</strong> is empty
+ or contains a valid value.
+</p>
+<pre>
+#define ITM_RXBUFFER_EMPTY 0x5AA55AA5 /* value identifying ITM_RxBuffer is ready for next character */
+</pre>
+<p>
+ <strong>ITM_ReceiveChar</strong> is used to receive a 8 bit value from the debug system. The function is nonblocking.
+ It returns the received character or '-1' if no character was available.
+</p>
+<pre>
+static __INLINE int ITM_ReceiveChar (void) {
+ int ch = -1; /* no character available */
+
+ if (ITM_RxBuffer != ITM_RXBUFFER_EMPTY) {
+ ch = ITM_RxBuffer;
+ ITM_RxBuffer = ITM_RXBUFFER_EMPTY; /* ready for next character */
+ }
+
+ return (ch);
+}
+</pre>
+
+<h3>ITM_CheckChar</h3>
+<p>
+ <strong>ITM_CheckChar</strong> is used to check if a character is received.
+</p>
+<pre>
+static __INLINE int ITM_CheckChar (void) {
+
+ if (ITM_RxBuffer == ITM_RXBUFFER_EMPTY) {
+ return (0); /* no character available */
+ } else {
+ return (1); /* character available */
+ }
+}</pre>
+
+
+<h2>ITM Debug Support in uVision</h2>
+<p>
+ uVision uses in a debug session the <strong>Debug (printf) Viewer</strong> window to
+ display the debug data.
+</p>
+<p>Direction microcontroller system -&gt; uVision:</p>
+<ul>
+ <li>
+ Characters received via ITM communication channel 0 are written in a printf style
+ to <strong>Debug (printf) Viewer</strong> window.
+ </li>
+</ul>
+
+<p>Direction uVision -&gt; microcontroller system:</p>
+<ul>
+ <li>Check if <strong>ITM_RxBuffer</strong> variable is available (only performed once).</li>
+ <li>Read character from <strong>Debug (printf) Viewer</strong> window.</li>
+ <li>If <strong>ITM_RxBuffer</strong> empty write character to <strong>ITM_RxBuffer</strong>.</li>
+</ul>
+
+<p class="Note">Note</p>
+<ul>
+ <li><p>Current solution does not use a buffer machanism for trasmitting the characters.</p>
+ </li>
+</ul>
+
+<h2>RTX Kernel awareness in uVision</h2>
+<p>
+ uVision / RTX are using a simple and efficient solution for RTX Kernel awareness.
+ No format overhead is necessary.<br>
+ uVsion debugger decodes the RTX events via the 32 / 16 / 8 bit ITM write access
+ to ITM communication channel 31.
+</p>
+
+<p>Following RTX events are traced:</p>
+<ul>
+ <li>Task Create / Delete event
+ <ol>
+ <li>32 bit access. Task start address is transmitted</li>
+ <li>16 bit access. Task ID and Create/Delete flag are transmitted<br>
+ High byte holds Create/Delete flag, Low byte holds TASK ID.
+ </li>
+ </ol>
+ </li>
+ <li>Task switch event
+ <ol>
+ <li>8 bit access. Task ID of current task is transmitted</li>
+ </ol>
+ </li>
+</ul>
+
+<p class="Note">Note</p>
+<ul>
+ <li><p>Other RTOS information could be retrieved via memory read access in a polling mode manner.</p>
+ </li>
+</ul>
+
+
+<p class="MsoNormal"><span lang="EN-GB">&nbsp;</span></p>
+
+<hr>
+
+<p class="TinyT">Copyright © KEIL - An ARM Company.<br>
+All rights reserved.<br>
+Visit our web site at <a href="http://www.keil.com">www.keil.com</a>.
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+
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