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<title>CMSIS Debug Support</title>
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<h1>CMSIS Debug Support</h1>
<p align="center">This file describes the CMSIS Debug support available with CMSIS V1.30.</p>
<p align="center">Version: 1.01 - 06. December 2010</p>
<p class="TinyT">Information in this file, the accompany manuals, and software is<br>
Copyright <20> ARM Ltd.<br>All rights reserved.
</p>
<hr>
<p><span style="FONT-WEIGHT: bold">Revision History</span></p>
<ul>
<li>Version 1.00: Initial Release. </li>
<li>Version 1.01: Internal Review. </li>
</ul>
<hr>
<h2>Contents</h2>
<ol>
<li class="LI2"><a href="#About">About</a></li>
<li class="LI2"><a href="#ITM_DbgAcc">Cortex-M3 / Cortex-M4 ITM Debug Access</a></li>
<li class="LI2"><a href="#DbgIn_DbgOut">Debug IN / OUT functions</a></li>
<li class="LI2"><a href="#ITM_DbgSup">ITM Debug Support in <20>Vision</a></li>
<li class="LI2"><a href="#RTX_KAW">RTX Kernel awareness in <20>Vision</a></li>
</ol>
<p>&nbsp;</p>
<h2><a name="About"></a>About</h2>
<p>
CMSIS provides for Cortex-M3 / Cortex-M4 processor based microcontrollers debug support via the Instrumented Trace Macrocell (ITM).
This document describes the available CMSIS Debug functions and the used methods.
</p>
<p>&nbsp;</p>
<h2><a name="ITM_DbgAcc"></a>Cortex-M3 / Cortex-M4 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>
<p>&nbsp;</p>
<h2><a name="DbgIn_DbgOut"></a>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 global variable is used. A simple mechanism detects if a character is received.
The project to test need to be build with debug information.
</p>
<p>
The global 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
ensure a proper handshake.
</p>
<pre>
extern volatile int32_t ITM_RxBuffer; /* variable to receive characters */
</pre>
<p>
A dedicated bit pattern is used to determine 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 int32_t ITM_ReceiveChar (void) {
int32_t 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 int32_t ITM_CheckChar (void) {
if (ITM_RxBuffer == ITM_RXBUFFER_EMPTY) {
return (0); /* no character available */
} else {
return (1); /* character available */
}
}</pre>
<p>&nbsp;</p>
<h2><a name="ITM_DbgSup"></a>ITM Debug Support in <20>Vision</h2>
<p>
<20>Vision uses in a debug session the <strong>Debug (printf) Viewer</strong> window to
display the debug data.
</p>
<p>Direction: Microcontroller -&gt; <20>Vision:</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: <20>Vision -&gt; Microcontroller:</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 mechanism for transmitting the characters.</p>
</li>
</ul>
<p>&nbsp;</p>
<h2><a name="RTX_KAW"></a>RTX Kernel awareness in <20>Vision</h2>
<p>
<20>Vision / RTX are using a simple and efficient solution for RTX Kernel awareness
via a CMSIS compliant interface. The <20>Vision 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 is retrieved via memory read accesses.</p>
</li>
</ul>
</body>
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